Stuart F Biggar
- Research Professor, Optical Sciences
- Member of the Graduate Faculty
Contact
- (520) 621-8168
- Meinel Optical Sciences, Rm. 605A
- Tucson, AZ 85721
- biggar@optics.arizona.edu
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Scholarly Contributions
Journals/Publications
- Thome, K. J., Arai, K., Tsuchida, S., & Biggar, S. F. (2008). Vicarious calibration of ASTER via the reflectance-based approach. IEEE Transactions on Geoscience and Remote Sensing, 46(10), 3285-3295.More infoAbstract: The reflectance-based vicarious calibration approach has been applied to the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) that is on the Terra platform. The results from three separate groups operating at the same sites at the same time are presented. The three groups show good agreement between each other, with differences between the groups being smaller than 4% in all bands ranging from 0.6 to 2.2 μm and with larger differences being seen at shorter wavelengths and beyond 2.2 μm. Comparisons between the groups and to the ASTER sensor are best at 1.66 μm (band 4), with differences between each group being less than 0.5% and all of the groups agreeing with ASTER to better than 5%. Differences in the visible and near infrared (VNIR) are larger, particularly prior to August 2002 when an update to the calibration processing was performed. These differences exceed 10% in some bands. In addition, the vicarious results appear to show a different trend than the onboard calibration for the VNIR indicating a possible problem with the onboard calibrator for bands 1-3. © 2008 IEEE.
- Biggar, S. F., Thome, K. J., Lockwood, R. B., & Miller, S. (2007). VNIR transfer radiometer for validation of calibration sources for hyperspectral sensors. Proceedings of SPIE - The International Society for Optical Engineering, 6677.More infoAbstract: We have designed, built, and calibrated a transfer radiometer for the VNIR region of the optical spectrum. The instrument is based on a "trap" detector configuration of large-area silicon detectors. The spectral bandpass of the nine bands between about 410 and 1050 nm is set by interference filters. This paper presents the design, characterization, and calibration of the radiometer.
- Buchanan, J., Dobler, J., Thome, K., & Biggar, S. (2006). Validation of a laser-based system for ground measurement of backscatter surface reflectance. Proceedings of SPIE - The International Society for Optical Engineering, 6296.More infoAbstract: The recent deployment of on-orbit active sensors operating at optical wavelengths requires new calibration methods to be investigated. In response to this, a ground-based active radiometer for measuring backscattered surface reflectance has been developed by the Remote Sensing Group at the University of Arizona. This instrument, known as the reflectometer, was designed to match the illumination and detection geometry of spaceborne lidar systems. The reflectometer uses a Nd:YAG laser operating at 1064 nm (with the capability of 532 nm), illuminates the target sample at normal incidence by use of a beam expander and fold mirror, then collects the reflected light at nadir through an aperture in the fold mirror. In order to reduce stray light, a 3 nm bandwidth filter centered on the laser wavelength is mounted in front of the silicon detector and a half cylinder shell encloses the optical system. Previous measurements at White Sands Missile Range, NM have produced results that are within 3% of coincident measurements using a field spectrometer. The results of these measurements are presented, including further laboratory testing using tarpaulin witness samples and future improvements of the original system design. In addition, comparison of reflectometer measurements to MODIS derived reflectance as it relates to on-orbit lidar retroreflection will be discussed. The benefits of validating MODIS derived reflectance will become essential with the launch of CALIPSO and its incorporation into the A-train.
- McCorkel, J., Thome, K., Biggar, S., & Kuester, M. (2006). Radiometric calibration of advanced land imager using reflectance-based results between 2001 and 2005. Proceedings of SPIE - The International Society for Optical Engineering, 6296.More infoAbstract: The Landsat series of sensors have supplied the remote sensing community with a continuous data set dating to the early 1970s. An important aspect of retaining the continuity of these data is that a Landsat follow-on as well as current Landsat instruments must be understood radiometrically throughout their mission. The Advanced Land Imager (ALI), for example, was developed as a prototype for the next generation of Landsat Instruments, and as such there was a significant effort to understand its radiometric characteristics as well as how it compares with previous Landsat sensors. The Remote Sensing Group at the University of Arizona has been part of this effort since the late 2000 launch of ALI through the use of the reflectance-based method of vicarious calibration. The reflectance-based approach consists of ground-based measurements of atmospheric conditions and surface reflectance at the time of satellite overpass to predict the at-sensor radiance seen by the sensor under study. The work compares results from the reflectance-based approach obtained from well-characterized test sites such as Railroad Valley Playa in Nevada and Ivanpah Playa in California as applied to ALI, Landsat-5 TM, and Landsat-7 EMT+. The results from the comparison use a total of 14 ALI dates spanning in time from 2001 to late 2005 and show that ALI agrees with the current radiometric results from TM and ETM+ to within 5%.
- Biggar, S. F., Thome, K. J., McCorkel, J. T., & D'Amico, J. M. (2005). Vicarious calibration of the ASTER SWIR sensor including crosstalk correction. Proceedings of SPIE - The International Society for Optical Engineering, 5882, 1-8.More infoAbstract: The Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) sensor on the Terra spacecraft has been providing remote sensing data for the past five years. ASTER has three separate sensor sections including a sensor with six bands in the shortwave infrared section of the spectrum. The radiometric calibration of the SWIR sensor has been updated from preflight values based on the on-board calibration sources. The SWIR sensor shows evidence of crosstalk between SWIR bands which is probably optical in origin. The crosstalk was present during preflight calibration and is present in all data collected in-flight including calibration data. The effects of crosstalk can be partially removed by applying a crosstalk correction program. This correction changes the calibration of the system. In this paper we apply a vicarious calibration to crosstalk corrected ASTER imagery over high reflectance desert test sites using a reflectance-based method. The updated calibration provides for better retrieval of spectral reflectance or radiance of ground targets in ASTER SWIR imagery.
- Brown, S. W., Johnson, B. C., Biggar, S. F., Zalewski, E. F., Cooper, J., Hajek, P., Hildum, E., Grant, P., Barnes, R. A., & Butler, J. J. (2005). Radiometric validation of NASA's Ames research center's sensor calibration laboratory. Applied Optics, 44(30), 6426-6443.More infoPMID: 16252654;Abstract: The National Aeronautics and Space Administration's (NASA's) Ames Research Center's Airborne Sensor Facility (ASF) is responsible for the calibration of several airborne Earth-viewing sensor systems in support of NASA Earth Observing System (EOS) investigations. The primary artifact used to calibrate these sensors in the reflective solar region from 400 to 2500 nm is a lamp-illuminated integrating sphere source. In September 1999, a measurement comparison was made at the Ames ASF Sensor Calibration Facility to validate the radiometric scale, establish the uncertainties assigned to the radiance of this source, and examine its day-to-day repeatability. The comparison was one of a series of validation activities overseen by the EOS Calibration Program to ensure the radiometric calibration accuracy of sensors used in long-term, global, remote-sensing studies. Results of the comparison, including an evaluation of the Ames Sensor Calibration Laboratory (SCL) measurement procedures and assigned radiometric uncertainties, provide a validation of their radiometric scale at the time of the comparison. Additionally, the maintenance of the radiance scale was evaluated by use of independent, long-term, multiyear radiance validation measurements of the Ames sphere source. This series of measurements provided an independent assessment of the radiance values assigned to integrating sphere sources by the Ames SCF. Together, the measurements validate the SCF radiometric scale and assigned uncertainties over the time period from September 1999 through July 2003. © 2005 Optical Society of America.
- Biggar, S., Thome, K., Geis, J., & Burkhart, C. (2004). Laser-based system for ground-based measurement of backscatter surface reflectance. International Geoscience and Remote Sensing Symposium (IGARSS), 3, 1955-1957.More infoAbstract: The on-orbit verification of spaceborne lidar systems relies on several approaches including those based on measuring the returned signal from the surface. This returned signal depends on both the atmospheric transmittance and the surface reflectance in the backscattered direction. Thus, knowledge of the surface reflectance is critical to such approaches. The Remote Sensing Group at the University of Arizona has developed a laser-based system to measure the backscatter surface reflectance at the ground for use in vicarious calibration of lidar systems. The device relies on a beam expander and fold mirror system to illuminate the ground. A detector is placed behind an aperture cut into the fold mirror to allow the backscattered signal to be measured. This work describes the results from the use of this system for the ground-based validation of GLAS using data from White Sands Missile Range in New Mexico. Measurements from a field-portable, passive spectrometer are also shown for comparison.
- Garland, W. C., Biggar, S. F., Zalewski, E. F., & Thome, K. J. (2004). Optical correction for multiple back reflections in an automated spectroradiometric measurement system. Proceedings of SPIE - The International Society for Optical Engineering, 5159, 82-90.More infoAbstract: The University of Arizona's Remote Sensing Group depends heavily upon automated solar radiometers and transfer radiometers for calibration of sensors. Interference filters are essential for these devices and accuracy in determining filter transmittance characteristics is crucial. The Remote Sensing Group uses a commercially available automated spectroradiometric measurement system equipped with a dual monochromator and a filter transmittance accessory for measuring filter transmittance. Examination of the design of transmittance attachment and the detector assembly indicated the possibility of multiple back reflections between an interference filter and the detector and that higher than expected transmittance values were likely. To reduce this, a fine annealed BK7 wedge with an 8-degree deviation angle was placed in the optical path between the transmittance accessory focusing lens and the detector. The purpose of this paper is to evaluate the performance of the system with the BK7 wedge. The effect of the wedge will be negligible for an absorption filter and possibly significant for interference filters in the band-pass region. Two interference filters were analyzed via three repeats for each of the following scenarios: broadband with and without the wedge and band-pass with and without the wedge. The broadband at low spectral resolution and band-pass at high spectral resolution trials had comparable results while the greatest percent difference in transmittance occurred in the out-of-band region due to the extremely small transmittance values associated with the noise level for the instrument in general and for each interference filter specifically. For the band-pass region, the trials yielded a 0.015 to 0.062 difference in transmittance with the greatest difference occurring in the large gradient zone between the band-pass and the out-of-band region. The wedge makes a significant difference in transmittance measurements.
- Thome, K., Biggar, S., & Choi, H. J. (2004). Vicarious calibration of Terra ASTER, MISR, and MODIS. Proceedings of SPIE - The International Society for Optical Engineering, 5542, 290-299.More infoAbstract: The Advanced Spaceborne Thermal Emission and Reflection and Radiometer (ASTER), Multi-angle Imaging Spectroradiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS) are all onboard the Terra platform. An important aspect of the use of MODIS, and other Earth Science Enterprise sensors, has been the characterization and calibration of the sensors and validation of their data products. The Remote Sensing Group at the University of Arizona has been active in this area through the use of ground-based test sites. This paper presents the results from the reflectance-base approach using the Railroad Valley Playa test site in Nevada for ASTER, MISR, and MODIS and thus effectively a cross-calibration between all three sensors. The key to the approach is the measurement of surface reflectance over a 1-km 2 area of the playa and results from this method shows agreement with MODIS to better than 5%. The paper examines biases between ASTER and the other two sensors in the VNIR due to uncertainties in the onboard calibrator for ASTER and in the SWIR due to an optical crosstalk effect.
- Biggar, S. F., Thome, K. J., & Wisniewski, W. (2003). Vicarious radiometric calibration of EO-1 sensors by reference to high-reflectance ground targets. IEEE Transactions on Geoscience and Remote Sensing, 41(6 PART I), 1174-1179.More infoAbstract: The Remote Sensing Group at the University of Arizona has been using ground targets for the in-flight vicarious calibration of airborne and satellite sensors since the early 1980s. Targets such as Railroad Valley Playa in north central Nevada and White Sands Missile Range in New Mexico have proven to be useful for this work. This paper presents the results from multiple vicarious calibration experiments at a variety of sites for two of the Earth Observing 1 (EO-1) optical sensors. The Advanced Land Imager (ALI) and Hyperion sensors operate in the visible and shortwave infrared portions of the spectrum. The ground sample distance of about 30 m works well for vicarious calibration and allows an easy comparison to legacy sensors such as the Enhanced Thematic Mapper Plus (ETM+) which has the same 30-m ground sample distance. The approach used in this work is to measure the surface reflectance and atmospheric properties during the sensor image acquisition. These data are used as input to a radiative transfer code which computes the top of atmosphere spectral radiance. This predicted radiance is compared to the radiance from the image of the site. Results show that the preflight calibrations of ALI and Hyperion are probably not consistent with in-flight performance of the instruments. New calibration coefficients adopted in December 2001 improve the comparison to the vicarious predictions.
- Bryant, R., Moran, S., McElroy, S. A., Holified, C., Thome, K. J., Miura, T., & Biggar, S. F. (2003). Data continuity of Earth Observing 1 (EO-1) Advanced Land Imager (ALI) and Landsat TM and ETM+. IEEE Transactions on Geoscience and Remote Sensing, 41(6 PART I), 1204-1214.More infoAbstract: The National Aeronautics and Space Administration (NASA) Landsat program has been dedicated to sustaining data continuity over the 20-year period during which Landsat Thematic Mapper (TM) and Enhanced TM Plus (ETM+) sensors have been acquiring images of the earth's surface. In 2000, NASA launched the Earth Observing-1 (EO-1) Advanced Land Imager (ALI) to test new technology that could improve the TM/ETM+ sensor series, yet ensure Landsat data continuity. The study reported here quantified the continuity of satellite-retrieved surface reflectance (ρ) for the three most recent Landsat sensors (Landsat-4 TM, Landsat-5 TM, and Landsat-7 ETM+) and the EO-1 ALI sensor. The study was based on ground-data verification and, in the case of the ETM+ to ALI comparison, coincident image analysis. Reflectance retrieved from all four sensors showed good correlation with ground-measured reflectance, and the sensor-to-sensor data continuity was excellent for all sensors and all bands. A qualitative analysis of the new ALI spectral bands (4p: 0.845-0.890 μm and 5p: 1.20-1.30 μm) showed that ALI band 5p provided information that was different from that provided by the ETM+/ALI shortwave infrared bands 5 and 7 for agricultural targets and that ALI band 4p has the advantage over the existing ETM+ near-infrared (NIR) band 4 and ALI NIR band 4 of being relatively insensitive to water vapor absorption. The basic conclusion of this study is that the four sensors can provide excellent data continuity for temporal studies of natural resources. Furthermore, the new technologies put forward by the EO-1 ALI sensor have had no apparent effect on data continuity and should be considered for the upcoming Landsat-8 sensor payload.
- Butler, J. J., Brown, S. W., Saunders, R. D., Johnson, B. C., Biggar, S. F., Zalewski, E. F., Markham, B. L., Gracey, P. N., Young, J. B., & Barnes, R. A. (2003). Radiometric measurement comparison on the integrating sphere source used to calibrate the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Landsat 7 Enhanced Thematic Mapper Plus (ETM+). Journal of Research of the National Institute of Standards and Technology, 108(3), 199-228.More infoAbstract: As part of a continuing effort to validate the radiometric scales assigned to integrating sphere sources used in the calibration of Earth Observing System (EOS) instruments, a radiometric measurement comparison was held in May 1998 at Raytheon/Santa Barbara Remote Sensing (SBRS). This comparison was conducted in support of the calibration of the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Landsat 7 Enhanced Thematic Mapper Plus (ETM+) instruments. The radiometric scale assigned to the Spherical Integrating Source (SIS100) by SBRS was validated through a comparison with radiometric measurements made by a number of stable, well-characterized transfer radiometers from the National Institute of Standards and Technology (NIST), the National Aeronautics and Space Administration's Goddard Space Flight Center (NASA's GSFC), and the University of Arizona Optical Sciences Center (UA). The measured radiances from the radiometers differed by ±3 % in the visible to near infrared when compared to the SBRS calibration of the sphere, and the overall agreement was within the combined uncertainties of the individual measurements. In general, the transfer radiometers gave higher values than the SBRS calibration in the near infrared and lower values in the blue. The measurements of the radiometers differed by ±4 % from 800 nm to 1800 nm compared to the SBRS calibration of the sphere, and the overall agreement was within the combined uncertainties of the individual measurements for wavelengths less than 2200 nm. The results of the radiometric measurement comparison presented here supplement the results of previous measurement comparisons on the integrating sphere sources used to calibrate the Multi-angle Imaging SpectroRadiometer (MISR) at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) at NEC Corporation, Yokohama, Japan.
- Thome, K. J., Biggar, S. F., & Wisniewski, W. (2003). Cross comparison of EO-1 sensors and other earth resources sensors to Landsat-7 ETM+ using Railroad Valley Playa. IEEE Transactions on Geoscience and Remote Sensing, 41(6 PART I), 1180-1188.More infoAbstract: The Remote Sensing Group at the University of Arizona has used ground-based test sites for the vicarious calibration of airborne and satellite-based sensors, of which the Railroad Valley Playa in north central Nevada has played a key role. This work presents a cross comparison of five satellite-based sensors that all imaged this playa on July 16, 2001. These sensors include the Advanced Land Imager and Hyperion on the Earth Observer-1 platform, the Landsat-7 Enhanced Thematic Mapper Plus (ETM+), Terra's Moderate Resolution Imaging Spectroradiometer, and Space Imaging's Ikonos. The approach atmospherically corrects the ETM+ data to derive surface reflectance for a 1 km × 1 km area of the playa and then uses these reflectances to determine a hyperspectral at-sensor radiance for each of the sensors taking into account the changes in solar zenith angle due to any temporal differences in the overpass times as well as differences in the view angles between the sensors. Results show that all of the sensors agree with ETM+ to within 10% in the solar reflective for bands not affected by atmospheric absorption. ETM+, MODIS, and ALI agree in all bands to better than 4.4% with better agreement in the visible and near infrared. Poorer agreement between Hyperion and other sensors appears to be due partially to poorer signal to noise ratio in the narrowband Hyperion datasets.
- Biggar, S. F., Thome, K. J., & Wisniewski, W. T. (2002). In-flight radiometric calibration of the advanced land imager and hyperion sensors on the EO-1 platform and comparisons with other earth observing sensors. Proceedings of SPIE - The International Society for Optical Engineering, 4814, 289-295.More infoAbstract: The radiometric calibration of the two optical sensors on the Earth Observing One satellite has been studied as a function of time since launch. The calibration has been determined by ground reference calibrations at well-characterized field sites, such as White Sands Missile Range and dry playas, and by reference to other sensors such as the Enhanced Thematic Mapper Plus (ETM+) on Landsat 7. The ground reference calibrations of the Advanced Land Imager (ALI) give results consistent with the on-board solar calibrator and show a significant shift since preflight calibration in the short wavelength bands. Similarly, the ground reference calibrations of Hyperion show a change since preflight calibration, however, for Hyperion the largest changes are in the short wave infrared region of the spectrum. Cross calibration of ALI with ETM+ is consistent with the ground reference calibrations in the visible and near infrared. Results showing the changes in radiometric calibration are presented.
- Krause, K., Biggar, S., Thome, K., Eagen, J., & Kenyon, D. (2002). On-orbit radiometric calibration using a solar diffuser. Proceedings of SPIE - The International Society for Optical Engineering, 4483, 135-145.More infoAbstract: Radiometric calibration of spacecraft sensors using an on-board diffuser has become an accepted method in recent years for sensors operating in the solar-reflective portion of the spectrum. In many of these approaches, the radiance from a sunlit diffuser is used to illuminate the full aperture and full optical path of the sensor. If both the bi-directional reflectance distribution function (BRDF) of the diffuser and the incident solar irradiance are known, the absolute radiance from the diffuser can be used to determine the absolute radiometric calibration of the sensor. In this work, a method for the absolute radiometric calibration using a diffuser made of S13G/LO paint for a silicon-based detector sensor with spectral bands similar to Landsat-7 ETM+ is discussed. The spectral BRDF of a witness sample of the diffuser was measured with the goniometric facility at the Remote Sensing Group of the Optical Sciences Center at the University of Arizona. A measured solar spectral irradiance spectra is used to model the radiance at the sensor entrance pupil. Also presented is a sensitivity analysis of the diffuser-leaving radiance as a function of sensor view and incident solar angle. This sensitivity analysis is used to provide an error estimate for the calibration of the sensor using a diffuser based on the S13G/LO paint.
- Kuester, M. A., Thome, K. J., Biggar, S. F., & Krause, K. S. (2002). Solar radiation based calibration of an airborne radiometer for vicarious calibration of earth observing sensors. Proceedings of SPIE - The International Society for Optical Engineering, 4483, 85-92.More infoAbstract: Airborne radiometric instruments are often used to collect radiance data, whether for producing remote sensing imagery, for use in vicarious calibration, or for atmospheric correction. Reflected radiance from a test site is detected by an Exotech model 100BX radiometer that contains four different spectral filters which coincide with the first four bands of Landsat Thematic Mapper (TM). These filters can be interchanged with filters that correspond to the first three multispectral bands of SPOT. Typically these radiometers are calibrated in a laboratory environment with incandescent radiance sources whose spectral outputs are known by some established standard. In the field, the radiometers are used with a different source than that used for the laboratory calibration, namely the sun. The solar radiation based calibration (SRBC) has been demonstrated to be an accurate calibration method for these instruments. The major advantage of this method is that the source for the calibration is the same source used in acquiring field measurements. In this work, solar radiation based calibration is compared to laboratory radiometric calibration done with a spherical integrating source (SIS) and a lamp source in the Remote Sensing Group (RSG) blacklab for airborne radiometers. Results of measurements taken over Ivanpah Playa on 6 July 2000 and 4 June 2000 by an Exotech model 100BX calibrated with these methods are presented and biases in the three different calibration methods are discussed.
- Rojas, F., Schowengerdt, R. A., & Biggar, S. (2002). Modulation transfer analysis for the moderate resolution imaging spectroradiometer (MODIS-AM). Proceedings of SPIE - The International Society for Optical Engineering, 4483, 222-230.More infoAbstract: The accuracy of the MODerate Resolution Imaging Spectroradiometer (MODIS) end data products is affected by the spatial response in the form of the Modulation Transfer Function (MTF). This effect is most noticeable near spatial transition periods where the contrast changes are high. This research effort is an estimate the MODIS MTF using a simplified model, based on Santa Barbara Research Center's MTF model. The simplified MTF model is incomplete, and MTF validation laboratory data are used to complete the model by estimating the unknown parameters. The laboratory data were taken using the Internal Alignment Collimator, a line spread function calibration instrument. Using the completed MTF model, a MTF correction filter is derived. The filter corrects the along-scan and along-track optical blurring and the along-scan non-zero integration time. The filter reduces the Point Spread Response (PSR) footprint by sharpening the response. The correction filter is applied to MODIS level 1B data using a scene from Mono Lake September 29, 2000 and a scene from the Maricopa Agricultural Center (MAC) September 26, 2000.
- Rojas, F., Schowengerdt, R. A., & Biggar, S. F. (2002). Early results on the characterization of the Terra MODIS spatial response. Remote Sensing of Environment, 83(1-2), 50-61.More infoAbstract: A project to characterize the Moderate Resolution-Imaging Spectroradiometer (MODIS) spatial response (SR) using preflight Modulation Transfer Function (MTF) validation data and on-orbit imagery is described, and the results from the analyses are presented. The preflight validation data are used to estimate the optical blurring parameters to complete a system MTF model for MODIS bands 1 and 2. The model and data indicate that the prelaunch MTF is higher for band 2 than for band 1. The on-orbit imagery is used in a two-image MTF estimation technique to characterize the on-orbit MTF for MODIS bands 1 and 2. Three data sets coincident with MODIS collects are used, Landsat-7 ETM+ imagery of Maricopa Agricultural Center, Arizona, on September 26, 2000 and May 24, 2001 and ASTER imagery of Mono Lake, CA, on September 29, 2000. The on-orbit MTFs obtained to date are consistent with prelaunch validation MTF measurements in the cross-track direction, but are less than prelaunch MTFs in the in-track direction. Further analysis is in progress to confirm these results. © 2002 Elsevier Science Inc. All rights reserved.
- Rojas, F., Schowengerdt, R. A., & Biggar, S. F. (2002). Error and correction for MODIS-AM's spatial response on the NDVI and EVI science products. Proceedings of SPIE - The International Society for Optical Engineering, 4814, 447-456.More infoAbstract: The accuracy of the Moderate Resolution Imaging Spectroradiometer (MODIS) end data products, such as the Vegetation Indices (VIs), are affected by MODIS's Spatial Response (SR). An error analysis is presented for the VI (MOD-13) product using Point Spread Response (PSR) data and improvement using a correction filter is demonstrated. The PSR data is a set of laboratory measurements that include electronic/optical cross-talk (pre- August 1998). The ensquared energy concept is applied to the PSR data to determine upper limits for the Far Field Response (FFR) (unwanted noise) that may be present in the MODIS data. The error analysis is presented using spectral variation, Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) which demonstrate that the science products are dependent on the sensor's SR. A correction filter for the MODIS SR shows a qualitative and quantitative improvement using a scene Railroad Valley scene, June 14th 2001 in which Landsat 7 ETM+ is used as the reference.
- Rojas, F., Schowengerdt, R. A., & Biggar, S. F. (2002). Validation of the on-orbit modulation transfer function for the moderate imaging spectroradiometer (MODIS-AM) using on-orbit calibration data and high contrast imagery. International Geoscience and Remote Sensing Symposium (IGARSS), 2, 973-975.More infoAbstract: Characterization of the on-orbit Modulation Transfer Function (MTF) for MODIS using two data sources is presented. One is the Spectroradiometric Calibration Assembly (SRCA) cross-track spatial calibration data. This data set has been acquired since MODIS's launch. The second source of on-orbit MTF validation data is high contrast imagery using coincident ETM+, ASTER and MODIS collects. The results obtained using both sources are presented. The SRCA data are acquired in the cross-track direction and show that the MTF is temporally stable. This data set does not include the aft-optics in the analysis. MTF results from the image analysis in the cross-track direction are consistent with the pre-launch estimates, but the in-track estimates are not as consistent with the pre-launch estimates.
- Biggar, S. F., Thome, K. J., Holmes, J. M., Kuester, M. A., & Schowengerdt, R. A. (2001). In-flight radiometric and spatial calibration of EO-1 optical sensors. International Geoscience and Remote Sensing Symposium (IGARSS), 1, 305-307.More infoAbstract: We have made an in-flight determination of the radiometric calibration of the ALI and Hyperion sensors on the EO-1 satellite. Ground and atmospheric measurements were made coincident with satellite images of high reflectance ground targets in both the southwestern United States and Argentina. Calibration coefficients derived from the in-flight experiments are compared to preflight values. We have also made preliminary comparisons of the spatial performance of ALI as compared to ETM+ on Landsat 7. Preliminary results are presented.
- Brown, S. W., Johnson, B., Yoon, H. W., Butler, J. J., Barnes, R. A., Biggar, S., Spyak, P., Thome, K., Zalewski, E., Helmlinger, M., Bruegge, C., Schiller, S., Fedosejevs, G., Gauthier, R., Tsuchida, S., & Machida, S. (2001). Radiometric characterization of field radiometers in support of the 1997 Lunar Lake, Nevada, experiment to determine surface reflectance and top-of-atmosphere radiance. Remote Sensing of Environment, 77(3), 367-376.More infoAbstract: A continuing series of field campaigns to Lunar Lake, Nevada, has been established to develop measurement protocols and assess the uncertainties of ground-based calibrations of on-orbit satellite sensors. In June 1997, an ensemble of field radiometers was deployed to validate the fundamental reflectance and radiance measurements of the Land Satellite (Landsat-5) Thematic Mapper (TM) and Satellite Pour l'Observation de la Terre (SPOT-2) Haute Resolution Visible (HRV) satellite instruments. Prior their deployment to Lunar Lake, many of the field instruments measured a common sphere source at the University of Arizona (UA). The results, presented in this work, showed variations in the relative stabilities of the field instruments, and demonstrate the need for in-depth characterization of field instruments for an accurate assessment of instrument performance and measurement uncertainty. © 2001 Published by Elsevier Science Inc.
- Nandy, P., Thome, K., & Biggar, S. (2001). Characterization and field use of a CCD camera system for retrieval of bidirectional reflectance distribution function. Journal of Geophysical Research D: Atmospheres, 106(D11), 11957-11966.More infoAbstract: Vicarious calibration and field validation is a critical aspect of NASA's Earth Observing System program. As part of calibration and validation research related to this project, the Remote Sensing Group (RSG) of the Optical Science Center at the University of Arizona has developed an imaging radiometer for ground-based measurements of directional reflectance. The system relies on a commercially available 1024 X 1024 pixel, silicon CCD array. Angular measurements are accomplished using a fish-eye lens that has a full 180° field of view with each pixel on the CCD array having a nominal 0.2° field of view. Spectral selection is through four interference filters centered at 470, 575, 660, and 835 nm. The system is designed such that the entire 180° field is collected at one time with a complete multispectral data set collected in under 2 min. The results of laboratory experiments have been used to determine the gain and offset of each detector element as well as the effects of the lens on the system response. Measurements of a stable source using multiple integration times and at multiple distances for a set integration time indicate the system is linear to better than 0.5% over the upper 88% of the dynamic range of the system. The point spread function (PSF) of the lens system was measured for several field angles, and the signal level was found to fall to less than 1% of the peak signal within 1.5° for the on-axis case. The effect of this PSF on the retrieval of modeled BRDFs is shown to be less than 0.2% out to view angles of 70°. The degree of polarization of the system is shown to be negligible for on-axis imaging but to have up to a 20% effect at a field angle of 70°. The effect of the system polarization on the retrieval of modeled BRDFs is shown to be up to 3% for field angles of 70° off nadir and with a solar zenith angle of 70°. Field measurements are made by mounting the camera to a boom mounted to a large tripod that is aligned toward south. This tripod obstructs sampling of the surface reflectance past 25° off nadir northward. The system is typically operated at a height of 1.5 m to view over a large sampling of surface features, such as cracks. To evaluate the surface BRDF, measurements are collected throughout the morning as a function of Sun angle. A single measurement consists of all four bands and a dark-current measurement. Data sets have been collected over several vicarious calibration sites and calibration tarpaulins. Comparisons with measurements made by a simple goniometer-based system indicate that the camera system is as accurate as the goniometer. Scattering phase function values derived from the camera system are fit to a modified Pinty-Verstraete equation. This function is shown to fit the data to better than 0.3% for data collected during an example RSG vicarious calibration experiment. Bidirectional reflectance data derived from the camera system also compare well to those predicted from the Walthall model. These BRDF models are critical for determining the applicability of measurements taken over small areas to represent the BRDF properties of an entire site, which in some cases is of the order of several kilometers in size. Copyright 2001 by the American Geophysical Union.
- Slater, P. N., Biggar, S. F., Palmer, J. M., & Thome, K. J. (2001). Unified approach to absolute radiometric calibration in the solar-reflective range. Remote Sensing of Environment, 77(3), 293-303.More infoAbstract: The need is identified for a unified approach to the preflight and in-flight absolute radiometric calibration of satellite sensors, which does not depend on the accurate transfer of lamp and detector calibrations from the laboratory to orbit. Such an approach is described that uses the sun to provide the link between preflight solar radiation-based calibration (SRBC), in-flight solar diffuser-based calibration, and vicarious calibration. Examples are given of these methods and uncertainty estimates are provided. It is shown that an uncertainty, with respect to solar exoatmospheric irradiance, of
- Teillet, P. M., Fedosejevs, G., Gauthier, R. P., O'Neill, N., Thome, K. J., Biggar, S. F., Ripley, H., & Meygret, A. (2001). A generalized approach to the vicarious calibration of multiple Earth observation sensors using hyperspectral data. Remote Sensing of Environment, 77(3), 304-327.More infoAbstract: The paper describes a new methodology that uses spatially extensive hyperspectral imagery as reference data to carry out vicarious radiometric calibrations for multiple satellite sensors. The methodology has been validated using data from a campaign at the Railroad Valley playa test site in Nevada in June 1998. The proof of concept has been further tested based on data acquisition campaigns at the Newell County rangeland test site in Alberta in August and October 1998. The rangeland test site in the Newell County region of Alberta is tested for its suitability as a calibration test site for satellite sensor systems. All three campaigns included ground-based measurements, satellite imagery, and airborne hyperspectral data. The airborne hyperspectral sensor data were acquired using the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) at Railroad Valley and the Compact Airborne Spectrographic Imager (casi) in all three campaigns. This paper describes the formulation and implementation of the new methodology, and radiometric calibration monitoring results obtained for five different sensors: NOAA-14 AVHRR, OrbView-2 SeaWiFS, SPOT-4 VGT, SPOT-1/2 HRV, and Landsat-5 TM. The results indicate that the nominal on-orbit radiometric calibrations of all the satellite sensors fit within their predicted uncertainties. The combination of both lower-reflectance and higher-reflectance test sites is shown to improve the quality of the calibration monitoring results. In particular, the combined QUASAR monitoring results obtained from the three airborne data acquisition days at the two test sites, encompassing five satellite sensors and a total of 40 spectral band cases, yield a correlation between QUASAR-based and nominal TOA radiances characterized by y = 1.026x - 1.26, and r2 = 0.990. Temporal extensions of QUASAR data sets to calibrate satellite sensors imaging the test site one or more days away from the airborne data acquisition day yield mixed results. Crown Copyright © 2001 Published by Elsevier Science Inc. All rights reserved.
- Thome, K., Biggar, S., & Slater, P. (2001). Effects of assumed solar spectral irradiance on intercomparisons of earth-observing sensors. Proceedings of SPIE - The International Society for Optical Engineering, 4540, 260-269.More infoAbstract: Recent work by the Remote Sensing Group at the University of Arizona has focused on the calibration and radiance validation of numerous sensors that are part of NASA's Earth Observation System and Earth Sciences Enterprise. The unique orbital combination of many of these sensors, both from formation flying as well as from multi-sensor platforms, provides an unprecedented opportunity with which to cross-compare results from these sensors. This work presents the results of cross-comparisons between the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), the Moderate Resolution Imaging Spectroradiometer (MODIS), the Enhanced Thematic Mapper Plus (ETM+) sensor, the MODIS-ASTER Simulator (MASTER), and the Advanced Land Imager (ALI). Differences in the cross-comparison between these sensors can be attributed to numerous causes, including spatial registration effects, spectral differences in the sensors, and temporal changes in the atmosphere and surface between sensor collections. One aspect of cross-comparison studies that is often overlooked is the solar spectral irradiance that is used by each sensor's calibration and validation teams, and with the advent of onboard diffusers the selection of the solar irradiance values becomes even more critical. This work describes the differences between typical solar irradiance spectra that are being used for the above-listed sensors and the effect of these spectra on the intercomparison of at-sensor radiances from earth-observing sensors.
- Barnes, R. A., Eplee Jr., R. E., Biggar, S. F., Thome, K. J., Zalewski, E. F., Slater, P. N., & Holmes, A. W. (2000). SeaWiFS transfer-to-orbit experiment. Applied Optics, 39(30), 5620-5631.More infoPMID: 18354559;Abstract: We present the results of an experiment designed to measure the changes in the radiometric calibration of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) from the time of its manufacture to the time of the start of on-orbit operations. The experiment uses measurements of the Sun at the manufacturer's facility to predict the instrument outputs during solar measurements immediately after launch. Because an onboard diffuser plate is required for these measurements, the experiment measures changes in the instrument-diffuser system. There is no mechanism in this experiment to separate changes in the diffuser from changes in the instrument. For the eight SeaWiFS bands, the initial instrument outputs on orbit averaged 0.8% higher than predicted with a standard deviation of 0.9%. The greatest difference was 2.1% (actual output higher than predicted) for band 3. The estimated uncertainty for the experiment is 3%. Thus the transfer-to-orbit experiment shows no changes in the radiometric sensitivities of the SeaWiFS bands - at the 3% level - from the completion of the instrument's manufacture to its insertion into orbit.
- Braga, A. B., Schowengerdt, R. A., Rojas, F., & Biggar, S. (2000). Calibration of the MODIS PFM SRCA for on-orbit, cross-track MTF measurement. Proceedings of SPIE - The International Society for Optical Engineering, 4135, 71-79.More infoAbstract: The SpectroRadiometric Calibration Assembly (SRCA) instrument performs spatial, radiometric, and spectral in-flight calibration of the MODIS PFM instrument on the TERRA satellite. In spatial mode, the SRCA is intended to characterize focal plane registration by measuring cross-track spatial shifts of individual detectors (channels), and in-track band centroid shifts. In this paper, we investigate the suitability of the SRCA to evaluate the MODIS MTF on-orbit. Using the SRCA to evaluate the MODIS MTF requires information on the optical quality of the SRCA itself, particularly since it is not designed specifically for MTF measurements. Because the SRCA illumination fills only 1/4 of the optical aperture of the MODIS system, the illumination conditions are significantly different from those of normal MODIS imaging. We characterize the SRCA's spatial performance by estimating its MTF from the pre-launch SRCA and Integration and Alignment Collimator (IAC) datasets, the IAC being assumed to be of significantly higher quality than the SRCA. This analysis shows that the SRCA, after calibration by comparison to the IAC, may serve as one source for on-orbit MTF measurements of MODIS PFM.
- Ding, X., Zalewski, E. F., & Biggar, S. F. (2000). Radiance stabilization of a calibration sphere source using two spectral bands. Proceedings of SPIE - The International Society for Optical Engineering, 4135, 88-95.More infoAbstract: In order to increase the repeatability of a radiance calibration sphere source we have developed a technique to digitally control the light source so as to maintain a constant radiance output. In this experiment a data acquisition system was used to read the photocurrents from two detectors that monitor the radiance at different wavelengths, the required change in the lamp current needed to maintain constant radiance was then calculated. Three different radiance control algorithms were tested: single band control, two-band minimum difference control and two-band spectral shape control. An electronic circuit using two moderate precision, digital-to-analog converters and a voltage-controlled power supply was developed to stabilize a small spherical integrating source. The test data show that two (or, by inference, more) spectral bands can be used in the radiance control of a sphere source with different algorithms for calculating the radiance stabilization correction function.
- Early, E. A., Barnes, P. Y., Johnson, B. C., Butler, J. J., Bruegge, C. J., Biggar, S. F., Spyak, P. R., & Pavlov, M. M. (2000). Bidirectional reflectance round-robin in support of the Earth Observing System program. Journal of Atmospheric and Oceanic Technology, 17(8), 1077-1091.More infoAbstract: Laboratory measurements of the bidirectional reflectance distribution function (BRDF) of diffuse reflectors are required to support calibration in the Earth Observing System (EOS) program of the National Aeronautics and Space Administration. To assess the ability of the instrument calibration laboratories to perform accurate BRDF measurements, a round-robin with the National Institute of Standards and Technology (NIST) as the central laboratory was initiated by the EOS Project Science Office. The round-robin parameters include sample type, wavelength, and incident and viewing angles. The results show that the participating calibration laboratories are, with a few exceptions due to experimental techniques or sample properties, generally able to measure BRDF for the round-robin parameters to within 2% of the values measured by NIST.
- Nandy, P., Thome, K., & Biggar, S. (2000). Sensitivity analysis of a CCD-based camera system for the retrieval of bidirectional reflectance distribution function for vicarious calibration. Proceedings of SPIE - The International Society for Optical Engineering, 4132, 279-289.More infoAbstract: The University of Arizona, Optical Sciences Center, Remote Sensing Group is involved with the vicarious calibration of satellite sensors in support of NASA's Earth Observing System (EOS) program. Sensor calibration coefficients are calculated by comparing sensor DN values to top of the atmosphere (TOA) radiance values, calculated from radiative transfer code (RTC). The RTC output is based on measurements of site spectral reflectance and atmospheric parameters at a selected test site. The bidirectional reflectance distribution function (BRDF) which relates the angular scattering of a given beam of incident radiation on a surface, is an important factor in these radiative transfer calculations. The inclusion of BRDF data into RTC calculations improves the level of accuracy of the vicarious calibration method by up to 5% over some target sites. BRDF data is also valuable in the validation of Multi-Angle Imaging Spectroradiometer (MISR) data sets. The Remote Sensing Group has developed an imaging radiometer system for ground-based measurements of BRDF. This system relies on a commercially-available 1024- by 1024-pixel silicon CCD array. Angular measurements are accomplished with a 8-mm focal length fisheye lens that has a full 180-degree field of view. Spectral selection is through four interference filters centered at 470, 575, 660 and 835 nm, mounted internally in the fisheye lens. This paper discusses the effect of calibration errors in this camera system on the retrieval of Hapke/Jacquemoud surface parameters from modeled BRDFs. The effect of these retrieved BRDFs on vicarious calibration results is discussed. Data processing schemes for the retrieval of these parameters from BRDF camera data sets are described. Based on these calculations, calibration requirements for digital camera BRDF-retrieval systems are presented.
- Rojas, F., Schowengerdt, R., Braga, A., & Biggar, S. (2000). Spatial analysis of the MODIS PFM channel alignment and far-field response using pre-resistor fix data. Proceedings of SPIE - The International Society for Optical Engineering, 4135, 60-70.More infoAbstract: We present a spatial analysis for the Visible (VIS), Near Infrared (NIR), Shortwave Midwave Infrared (S/MWIR), and Long Wave Infrared (LWIR) focal planes of Moderate Resolution Imaging SpectroRadiometer (MODIS) Pre-Flight Model (PFM) on the Terra platform. The analysis includes focal plane detector (channel) alignment, optical/electronic cross-talk, and Far Field Response (FFR). The study is performed on pre-launch laboratory Point Spread Response (PSR) data, and three sets of alignment data both taken prior to August 1998. The PSR and alignment data are displayed using the Focal Plane Viewer (FPV), a software utility developed to aid in the study. Channel measurement and band summaries are presented for each focal plane. The findings for optical/electronic cross-talk are based on the PSR and the alignment data. The calculation of Ensquared Energy (EE) from the PSR data characterizes the far-field response for channel 5.
- Barnes, R. A., Eplee Jr., R. E., Biggar, S. F., Thome, K. J., Zalewski, E. F., Slater, P., & Holmes, A. W. (1999). SeaWiFS postlaunch technical report series. Volume 5, the SeaWiFS solar radiation-based calibration-and the transfer-to-orbit experiment. NASA Technical Memorandum - SeaWIFS Postlaunch Technical Report Series, 1-28.More infoAbstract: The solar radiation-based calibration (SRBC) of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) was performed on 1 November 1993. Measurements were made outdoors in the courtyard of the instrument manufacturer. SeaWiFS viewed the solar irradiance reflected from the sensor's diffuser in the same manner as viewed on orbit. The calibration included measurements using a solar radiometer designed to determine the transmittances of principal atmospheric constituents. The primary uncertainties in the outdoor measurements are the transmission of the atmosphere and the reflectance of the diffuser. Their combined uncertainty is about 5 or 6%. The SRBC also requires knowledge of the extraterrestrial solar spectrum. Four solar models are used. When averaged over the responses of the SeaWiFS bands, the irradiance models agree at the 3.6% level, with the greatest difference for SeaWiFS band 8. The calibration coefficients from the SRBC are lower than those from the laboratory calibration of the instrument in 1997. For a representative solar model, the ratios of the SRBC coefficients to laboratory values average 0.962 with a standard deviation of 0.012. The greatest relative difference is 0.946 for band 8. These values are within the estimated uncertainties of the calibration measurements. For the transfer-to-orbit experiment, the measurements in the manufacturer's courtyard are used to predict the digital counts from the instrument on its first day on orbit (1 August 1997). This experiment requires an estimate of the relative change in the diffuser response for the period between the launch of the instrument and its first solar measurements on orbit (9 September 1997). In relative terms, the counts from the instrument on its first day on orbit averaged 1.3% higher than predicted, with a standard deviation of 1.2% and a greatest difference of 2.4% for band 7. The estimated uncertainty for the transfer-to-orbit experiment is about 3 or 4%.
- Biggar, S. F., Thome, K. J., Spyak, P. R., & Zalewski, E. F. (1999). Solar-radiation based calibration in the range 740 to 2400 nm. Proceedings of SPIE - The International Society for Optical Engineering, 3870, 228-233.More infoAbstract: Optical instruments are normally calibrated with incandescent irradiance or radiance sources. Recently, accurate calibrations using solar radiation have been demonstrated in the visible and near-IR regions (VNIR). The solar-radiation based calibration (SRBC) has a major advantage in that the calibration source is the same source used on-orbit by earth-viewing remote sensing sensors such as the ASTER, MODIS, and Landsat 7 ETM + sensors. In this paper, such a radiometer calibration covering the region between 740 and 2400 nm is presented and compared with lamp-based laboratory calibrations. This work extends the spectral range over which a calibration using solar-radiation has been made.
- Butler, J. J., Johnson, B., Brown, S. W., Yoon, H. W., Barnes, R. A., Markham, B. L., Biggar, S. F., Zalewski, E. F., Spyak, P. R., Cooper, J. W., & Sakuma, F. (1999). Radiometric measurement comparisons using transfer radiometers in support of the calibration of NASA's Earth Observing System (EOS) sensors. Proceedings of SPIE - The International Society for Optical Engineering, 3870, 180-192.More infoAbstract: The National Aeronautics and Space Administration's (NASA's) Earth Observing System (EOS) Project Science Office has sponsored a number of radiometric measurement comparisons with the main purpose of validating the radiometric scale assigned to the integrating spheres by the instrument builders. This article describes the radiometric measurement comparisons, the use of stable transfer radiometers to perform the measurements, and the measurement approaches and protocols used to validate integrating sphere radiances.
- Nandy, P., Thome, K., & Biggar, S. (1999). Laboratory characterization of a CCD camera system for retrieval of bi-directional reflectance distribution function. Proceedings of SPIE - The International Society for Optical Engineering, 3870, 243-253.More infoAbstract: The Remote Sensing Group of the Optical Science Center at the University of Arizona has developed a four-band, multi-spectral, wide-angle, imaging radiometer for the retrieval of the bi-directional reflectance distribution function (BRDF) for vicarious calibration applications. This article discusses the results of laboratory characterization of the system to determine linearity of the detector, point spread function (PSF) and polarization effects. The results indicate that BRDF data from the camera system is accurate to better than 1% at field angles of less than 20 degrees, and to 3% out to 70 degrees.
- Teillet, P. M., Fedosejevs, G., Gauthier, R. P., Shin, R. T., O'Neill, N. T., Thome, K. J., Biggar, S. F., Ripley, H., & Meygret, A. (1999). Radiometric calibration of multiple Earth observation sensors using airborne hyperspectral data at the Newell County rangeland test site. Proceedings of SPIE - The International Society for Optical Engineering, 3750, 470-481.More infoAbstract: A single data set of spatially extensive hyperspectral imagery is used to carry out vicarious calibrations for multiple Earth observation sensors. Results are presented based on a data acquisition campaign at the Newell County rangeland test site in Alberta in October 1998, which included ground-based measurements, satellite imagery, and airborne case hyperspectral data. This paper presents new calibration monitoring results obtained for NOAA-14 AVHRR, OrbView-2 SeaWiFS, SPOT-4 VGT, Landsat-5 TM, and SPOT-2 HRV.
- Thome, K. J., LaMarr, J. H., Biggar, S. F., & Lopez, A. S. (1999). Ground-reference calibration of Landsat-7 ETM+. Proceedings of SPIE - The International Society for Optical Engineering, 3870, 234-242.More infoAbstract: Ground-reference techniques for the Enhanced Thematic Mapper Plus (ETM+) on Landsat 7 are described. The techniques are similar to those used for many years for Landsat-5 Thematic Mapper (TM). Recent results with the Landsat-5 TM are presented, including comparisons with hyperspectral, airborne imaging data. These results show that the Landsat sensor has remained stable within the 5% uncertainty of the ground-reference methods for the last five years. The airborne imagery is also used to show uncertainties due to registration errors, spectral differences, and spatial resolution differences in cross-comparison techniques planned for Earth Observing System sensors. In addition to the use of the traditional methods and test sites, a smaller test site local to the University of Arizona area is being evaluated for use with ETM+. This site, while not as bright, spatially-uniform and large as typical sites, allows more frequent calibrations and hopefully a better understanding of the calibration as a function of time. The selection of the test site, its properties, and example results of calibration of Landsat-5 TM are presented.
- Barnes, P. Y., Early, E. A., Johnson, B. C., Butler, J. J., Bruegge, C. J., Biggar, S., Spyak, P. R., & Pavlov, M. (1998). Intercomparisons of reflectance measurements. Proceedings of SPIE - The International Society for Optical Engineering, 3425, 10-15.More infoAbstract: A comparison of spectral diffuse reflectance between different national standards laboratories is being planned under the direction of the Comité Consultatif de Photométrie et Radiométrie (CCPR). A similar comparison of bidirectional reflectance distribution factor among laboratories in the United States in support of optical remote sensing measurements is nearing completion. Since this comparison provides valuable lessons for the one organized by the CCPR, pertinent results and their implications are presented.
- Biggar, S. F. (1998). Calibration of a visible and near-infrared portable transfer radiometer. Metrologia, 35(4), 701-706.More infoAbstract: A portable transfer radiometer covering the spectral range 400 nm to 900 nm has been built and calibrated. This radiometer was designed to measure the output of spherical integrating sources with large apertures such as those used to calibrate spacecraft sensors for the Earth Observing System (EOS) of the National Aeronautics and Space Administration (NASA). The radiometer is a simple, robust, narrowband multifilter instrument using a silicon trap detector. The temperature of the filters, apertures, detectors and electronics is controlled slightly above ambient. There are no imaging optics and the radiometer throughput is controlled by Invar-spaced apertures. The radiometer has been calibrated by two methods. First, the radiometer was calibrated in an irradiance mode by use of a National Institute of Standards and Technology (NIST) FEL lamp. Second, a Solar-Radiation-Based Calibration (SRBC) was carried out, in which the radiometer viewed a panel, calibrated with a bidirectional reflectance distribution function (BRDF), illuminated by the Sun. Differences between the NIST calibration and the SRBC method for a recent solar spectrum are quite small: less than 2.1 % for the seven bands between 412 nm and 868 nm, and well within the estimated uncertainties for the two calibration methods.
- Johnson, B. C., Barnes, P. Y., O'Brian, T., Butler, J. J., Bruegge, C. J., Biggar, S., Spyak, P. R., & Pavlov, M. M. (1998). Initial results of the bidirectional reflectance characterization round-robin in support of EOS. Metrologia, 35(4), 609-613.More infoAbstract: Laboratory measurements of the bidirectional reflectance distribution function (BRDF) of diffusely reflecting samples are required to support calibration in the Earth Observing System (EOS) programme of the National Aeronautics and Space Administration (NASA). To assess the ability of the instrument calibration laboratories to perform accurate BRDF measurements, a round-robin comparison with the National Institute of Standards and Technology (NIST) as the central laboratory was initiated by the EOS Project Science Office. The comparison parameters, which include measurement wavelength, spectral bandwidth, illumination and viewing geometry, sample type and alignment, and data format, were selected in consultation with the participants. The participants were selected based on their roles as metrology laboratories with direct connections to EOS or other international Earth remote-sensing satellite programmes. This paper briefly describes the format of the comparison, the status of the first round, and some preliminary results.
- Nandy, P., Thome, K., & Biggar, S. (1998). Instrument for retrieval of BRDF data for vicarious calibration. International Geoscience and Remote Sensing Symposium (IGARSS), 2, 562-564.More infoAbstract: The University of Arizona's Remote Sensing Group has performed vicarious calibrations of satellite and airborne sensors since the mid-1980s. Improvements of the accuracy of these techniques requires that the bi-directional reflectance of the test sites be characterized. The Remote Sensing Group has developed a four-band, imaging radiometer based on a two-dimensional CCD array and 8-mm fisheye lens for the retrieval of bidirectional reflectance. This paper describes the design of this radiometer and the methods used to calibrate the system. The calibration is based upon measurements of a 40-inch spherical integrating source and we describe a method to separate the spatial inhomogeneity of the source from that of the CCD array. Early data collected with this instrument of test sites at White Sands Missile Range and Lunar Lake Playa are presented and show good agreement with previous data collected at these or similar sites.
- Schmid, B., Spyak, P. R., Biggar, S. F., Wehrli, C., Sekler, J., Ingold, T., Mätzler, C., & Kämpfer, N. (1998). Evaluation of the applicability of solar and lamp radiometric calibrations of a precision Sun photometer operating between 300 and 1025 nm. Applied Optics, 37(18), 3923-3941.More infoPMID: 18273360;Abstract: Over a period of 3 years a precision Sun photometer (SPM) operating between 300 and 1025 nm was calibrated four times at three different high-mountain sites in Switzerland, Germany, and the United States by means of the Langley-plot technique. We found that for atmospheric window wavelengths the total error (2σ-statistical plus systematic errors) of the calibration constants V0 (λ), the SPM voltage in the absence of any attenuating atmosphere, can be kept below 1.6% in the UV-A and blue, 0.9% in the mid-visible, and 0.6% in the near-infrared spectral region. For SPM channels within strong water-vapor or ozone absorption bands a modified Langley-plot technique was used to determine V0 (λ) with a lower accuracy. Within the same period of time, we calibrated the SPM five times using irradiance standard lamps in the optical labs of the Physikalisch-Meteorologisches Observatorium Davos and World Radiation Center, Switzerland, and of the Remote Sensing Group of the Optical Sciences Center, University of Arizona, Tucson, Arizona. The lab calibration method requires knowledge of the extraterrestrial spectral irradiance. When we refer the standard lamp results to the World Radiation Center extraterrestrial solar irradiance spectrum, they agree with the Langley results within 2% at 6 of 13 SPM wavelengths. The largest disagreement (4.4%) is found for the channel centered at 610 nm. The results of these intercomparisons change significantly when the lamp results are referred to two different extraterrestrial solar irradiance spectra that have become recently available. © 1998 Optical Society of America.
- Smith, J., Thome, K., Crowther, B., & Biggar, S. (1998). Field evaluation of a diffuse to global irradiance meter for vicarious calibration. International Geoscience and Remote Sensing Symposium (IGARSS), 2, 663-665.More infoAbstract: Vicarious calibration methods have been developed to calibrate radiometric sensors in-flight. One such method, the irradiance-based method, requires the measurement of the diffuse-to-global (diffuse-to-total) irradiance ratio. A diffuse-to-global irradiance meter has recently been developed by the Remote Sensing Group at the University of Arizona. The instrument uses a baffled integrating sphere as its collector and an occulting disc to block the sun for diffuse-irradiance measurements. Data are collected at 10-nm intervals from 350 to 1100 nm. In this paper, two methods are used to evaluate this instrument. The first relies on the well-known Langley method to determine atmospheric optical thickness from measurements of the direct solar irradiance derived from the difference between the global and diffuse irradiances. Secondly, the diffuse-to-global ratio was used to predict the radiance at the top of the atmosphere. These radiance results are compared to those from the reflectance-based method as well as those derived from data collected by the AVIRIS sensor. Data were collected at Lunar Lake Nevada June 23,24,25 1997 and White Sands Missile Range on October 31 and November 1, 1997. Comparison of optical thickness obtained from data collected by a well-understood solar radiometer show differences in optical thickness ranging from 0.003 minimum to 0.018 maximum. These results are encouraging as they indicate that there are no major effects due to inhomogeneities in the spherical collector.
- Yoon, H. W., Johnson, B. C., Kelch, D., Biggar, S., & Spyak, P. R. (1998). A 400 nm to 2500 nm absolute spectral radiance comparison using filter radiometers. Metrologia, 35(4), 563-568.More infoAbstract: An integrating-sphere source developed by MTL Systems, Inc. was calibrated for them by a commercial standards laboratory traceable to the National Institute of Standards and Technology (NIST), resulting in values of spectral radiance in the 400 nm to 2500 nm spectral region. The spectral radiance of the MTL sphere source was then measured using three filter radiometers, also NIST-traceable, that were developed for the Earth Observing System (EOS). In the visible and near-infrared, the values from two Si-photodiode filter radiometers and the supplied calibration values agree within their mutual uncertainties, but in the short-wave infrared, the agreement between the filter-radiometer results and the calibration values is less satisfactory. The reason for this discrepancy is not understood, and additional measurements should be performed.
- Crowther, B. G., Thome, K. J., Biggar, S. F., & Burkhart, C. J. (1997). Internally baffled integrating sphere cosine collector. Proceedings of SPIE - The International Society for Optical Engineering, 3117, 246-252.More infoAbstract: Cosine collector designs based on internally baffled integrating spheres have been difficult to evaluate in the past due to the expense and difficulty of building the spheres and measuring their angular response. A Monte Carlo model has been developed that enables integrating sphere designs to be evaluated relatively quickly and efficiently. The model was applied to an integrating sphere employing an internal conical baffle. The angular response and overall throughput of the sphere as predicted by the model are presented and discussed. Construction of the sphere was recently completed and the relative angular response was measured in the field. A solar radiometer was used to determine the solar irradiance at the entrance aperture of the sphere, enabling the response of the sphere to be found as a function of the solar zenith angle. Results of the measurement are presented and compared with the model results. ©2004 Copyright SPIE - The International Society for Optical Engineering.
- Johnson, B. C., Sakuma, F., Butler, J. J., Biggar, S. F., Cooper, J. W., Ishida, J., & Suzuki, K. (1997). Radiometric measurement comparison using the Ocean Color Temperature Scanner (OCTS) visible and near infrared integrating sphere. Journal of Research of the National Institute of Standards and Technology, 102(6), 627-646.More infoAbstract: As a part of the pre-flight calibration and validation activities for the Ocean Color and Temperature Scanner (OCTS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color satellite instruments, a radiometric measurement comparison was held in February 1995 at the NEC Corporation in Yokohama, Japan. Researchers from the National Institute of Standards and Technology (NIST), the National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC), the University of Arizona Optical Sciences Center (UA), and the National Research Laboratory of Metrology (NRLM) in Tsukuba, Japan used their portable radiometers to measure the spectral radiance of the OCTS visible and nearinfrared integrating sphere at four radiance levels. These four levels corresponded to the configuration of the OCTS integrating sphere when the calibration coefficients for five of the eight spectral channels, or bands, of the OCTS instrument were determined. The measurements of the four radiometers differed by -2.7 % to 3.9 % when compared to the NEC calibration of the sphere and the overall agreement was within the combined measurement uncertainties. A comparison of the measurements from the participating radiometers also resulted in agreement within the combined measurement uncertainties. These results are encouraging and demonstrate the utility of comparisons using laboratory calibration integrating sphere sources. Other comparisons will focus on instruments that are scheduled for spacecraft in the NASA study of climate change, the Earth Observing System (EOS).
- Parada Jr., R. J., Thome, K. J., Biggar, S. F., Santer, R. P., & LaMarr, J. H. (1997). Radiometer calibrations using solar radiation. Proceedings of SPIE - The International Society for Optical Engineering, 3117, 253-261.More infoAbstract: Airborne radiometric instruments are often used to collect calibrated radiance data, whether for producing remotely- sensed imagery, for use in vicarious calibration, or for atmospheric correction. Typically, these radiometers are calibrated in a laboratory environment using source whose spectral outputs are traceable to some established, man-made standard. In the field, these devices are used with a different source: solar radiation. The use of solar radiation as a calibration source should therefore be considered when calibration radiometers used to collect energy in the solar reflective region. This paper presents a novel method of calibration which makes use of scattered solar radiation as the source. This technique is particularly applicable for airborne radiometers intended to view low-reflectance surfaces, since the magnitude and spectral distribution of the collected energy is very similar to that of skylight, especially at shorter visible wavelengths. The method is applied to visible and near-IR bands of a Barnes Modular Multispectral 8-channel Radiometer. A sensitivity study was performed for the method and an associated uncertainty analysis is presented. The calibration results are compared to a second, more established solar-based method whose source is directly- transmitted solar irradiance. ©2004 Copyright SPIE - The International Society for Optical Engineering.
- Thome, K. J., Crowther, B. C., & Biggar, S. F. (1997). Reflectance- and irradiance-based calibration of landsat-5 thematic mapper. Canadian Journal of Remote Sensing, 23(4), 309-317.More infoAbstract: The reflectance- and irradiance-based methods are used to determine an absolute, radiometric calibration of Landsat-5 Thematic Mapper for the solar reflective portion of the spectrum for data using the National Landsat Archive Production System format. Results are given for a calibration campaign at White Sands Missile Range in New Mexico in December 1996. The results of the two methods agree to better than 6% and comparisons with predicted, at-sensor radiances based on the gains and biases supplied with the data tape were found to differ by 1% to 41%. The results are also presented with reference to previously determined results from different processing techniques. The large differences between these results and the current values indicate the importance of consistent use of calibration for remotely-sensed data.
- Thome, K., Markham, B., Barker, J., Slater, P., & Biggar, S. (1997). Radiometric calibration of Landsat. Photogrammetric Engineering and Remote Sensing, 63(7), 853-858.More infoAbstract: The radiometric calibration of the sensors on the Landsat series of satellites is a contributing factor to the success of the Landsat data set. The calibration of these sensors has relied on the preflight laboratory work as well as on inflight techniques using on-board calibrators and vicarious techniques. Descriptions of these methods and systems are presented. Results of the on-board calibrators and reflectance-based, ground reference calibrations of Landsat 5 Thematic Mapper are presented that indicate the absolute radiometric calibration of bands 1 to 4 should have an uncertainty of less than 5.0 percent. Bands 5 and 7 have slightly higher uncertainties, but should be less than 10 percent. The results also show that the on-board calibrators are of higher precision than the vicarious calibration but that the vicarious calibration results should have higher accuracy.
- Mueller, J. L., Johnson, B. C., Cromer, C. L., Hooker, S. B., McLean, J. T., & Biggar, S. F. (1996). The third SeaWiFS Intercalibration Round-Robin Experiment (SIRREX-3) , 19-30 September 1994. NASA Technical Memorandum - SeaWiFS Technical Report Series, 34.More infoAbstract: This report presents results of the third Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Intercalibration Round-Robin Experiment (SIRREX-3). Specral irradiances of FEL lamps belonging to each participant were intercompared by reference to the National Institute of Standards & Technology (NIST) scale of spectral irradiance using secondary standard lamps F268, F269 and F182, with a Type A uncertainty between 1.1-1.5%. This level of uncertainty was achieved despite difficulties with lamp F269. with two exceptions, spectral radiance values of integrating sphere sources were measured during SIRREX-3 with uncertainties in temporal stability of less than 0.3% and absolute uncertainties of 1.5-2.0%. Plaque reflectances were intercompared with an uncertainty of about 1-2%, but the absolute uncertainty is undefined. -from Authors
- Slater, P. N., & Biggar, S. F. (1996). Suggestions for radiometric calibration coefficient generation. Journal of Atmospheric and Oceanic Technology, 13(2), 376-382.More infoAbstract: The great emphasis that studies of global change have placed on accurate absolute radiometric calibration of satellite sensors has led to the development of many new onboard and vicarious calibration techniques. With the launch in 1998 of the first Earth Observing System sensors, calibration scientists will, for the first time, be confronted by a large number of calibration coefficients for each band of each sensor obtained using these different techniques. The question that arises is, what is the way to combine these coefficients to maximize the accuracy of sensor calibration as a function of time? This paper discusses the problem and suggests procedural criteria followed by a procedure for calibration coefficient generation. Emphasis is placed on the use of onboard results in an on-line production of calibration coefficients and the modification of these coefficients, at perhaps 3-month intervals, by reference to vicarious calibration results obtained during that period. Reference is made to the calibration SPOT as a first simple example of such an approach.
- Slater, P. N., Biggar, S. F., Thome, K. J., Gellman, D. I., & Spyak, P. R. (1996). Vicarious radiometric calibrations of EOS sensors. Journal of Atmospheric and Oceanic Technology, 13(2), 349-359.More infoAbstract: Four methods for the in-flight radiometric calibration and cross calibration of multispectral imaging sensors are described. Three make use of ground-based reflectance, irradiance, and radiance measurements in conjunction with atmospheric measurements and one compares calibrations between sensors. Error budgets for these methods are presented and their validation is discussed by reference to SPOT and TM results and shown to meet the EOS requirements in the solar-reflective range.
- Slater, P. N., Biggar, S. F., Palmer, J. M., & Thome, K. J. (1995). Unified approach to pre- and in-flight satellite-sensor absolute radiometric calibration. Proceedings of SPIE - The International Society for Optical Engineering, 2583, 130-141.More infoAbstract: The need is identified for a unified approach to the preflight and in-flight absolute radiometric calibration of satellite sensors, which does not depend on the accurate transfer of lamp and detector calibrations from the laboratory to orbit. Such an approach is described that uses the sun to provide the link between preflight solar-radiation-based calibration, in-flight solar- diffuser-based calibration, and vicarious calibration. An example is given of each of these methods and uncertainty budgets are provided. It is shown that an uncertainty, with respect to solar exo-atmospheric irradiance, of less than 3%, one sigma, can be attained for each method and that each can, if needed, be related to national laboratory standards. In addition to providing the link between preflight and in-flight on-board calibrations, this unified approach also fills the critical need to relate these calibrations to those of the radiometers used for vicarious calibration and data-product, field-validation measurements, by also referencing them to the same solar-irradiance scale.
- Slater, P. N., Biggar, S. F., Thome, K. J., Gellman, D. I., & Spyak, P. R. (1995). In-flight radiometric calibration of ASTER by reference to well-characterized scenes. Proceedings of SPIE - The International Society for Optical Engineering, 2317, 49-60.More infoAbstract: ASTER will be calibrated in the laboratory by reference to sources traceable to NRLM and NIST standards and through the use of transfer radiometers. Partial aperture on-board calibration systems will be used in the solar-reflective range and an on-board blackbody source will be used in the infrared. An important independent source of calibration data will be provided through the in-flight radiometric calibration of ASTER by reference to well- characterized scenes. The latter is the subject of this paper. Methods that make use of ground reflectance and radiance measurements made simultaneously with atmospheric measurements at selected sites and used as input to radiative transfer codes are described. The results of error analyses are presented indicating that, depending on the method used, the predicted uncertainties fall between ± 2.8% and ± 4.9%, for the solar-reflective range. In the thermal infrared, the goal is an uncertainty of less than 1 K. A method that provides in-flight cross calibrations with other sensors also is described.
- Biggar, S. F., Slater, P. N., & Gellman, D. I. (1994). Uncertainties in the in-flight calibration of sensors with reference to measured ground sites in the 0.4-1.1 μm range. Remote Sensing of Environment, 48(2), 245-252.More infoAbstract: This article describes the error sources for three in-flight sensor calibration methods used by the Remote Sensing Group of the Optical Sciences Center at the University of Arizona. The three methods are the reflectance-, improved reflectance-, and radiance-based methods, which all reference the earth-atmosphere system. The sources of error or uncertainty for each method are discussed, and an estimate of the percent uncertainty associated with each source is made for conditions similar to those actually used for calibrations at White Sands, New Mexico. The results of in-flight calibrations are compared to those of the on-board lamp calibration system for a SPOT HRV camera. © 1994.
- Biggar, S. F., Thome, K. J., Slater, P. N., Balick, L. K., & Golanics, C. J. (1994). Solar-radiation-based absolute calibration of optical sensors: SeaWiFS and a Daedalus 1268. International Geoscience and Remote Sensing Symposium (IGARSS), 4, 1992-1994.More infoAbstract: We have developed a solar-radiation-based calibration method for the radiometric calibration of satellite sensors with a solar diffuser such as that used on SeaWiFS. A similar method using a diffuser at ground level can be used to calibrate airborne sensors such as the Daedalus 1268 sensor operated by EG&G in a helicopter. The atmospheric transmittance is measured while measurements of a solar illuminated diffuser panel are made by the instrument being calibrated. Measurements of the panel are also taken with the direct solar beam blocked. The difference gives the signal due to the attenuated solar beam. The major advantage of this method is that the source for the calibration, the sun, is the same source used in measurements. Results of calibrations of SeaWiFS and a Daedalus scanner are presented.
- Thome, K. J., Biggar, S. F., Gellman, D. I., & Slater, P. N. (1994). Absolute-radiometric calibration of Landsat-5 thematic mapper and the proposed calibration of the advanced spaceborne thermal emission and reflection radiometer. International Geoscience and Remote Sensing Symposium (IGARSS), 4, 2295-2297.More infoAbstract: The reflectance-based method is used to determine an absolute-radiometric calibration of Landsat-5 Thematic Mapper for the solar reflective portion of the spectrum. Results are given for data collected at White Sands Missile Range in New Mexico on 1992-08-15 and 1993-10-21. These results are compared to those obtained from applying an identical approach to data collected in 1984, 1985, and 1988. Results indicate sensor degradation in the first three bands with greatest degradation at the shortest wavelengths. The reflectance-based method is also to be used for the in-flight, absolute-radiometric calibration of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) to be launched on the Earth Observing System's AM1 platform. We describe the anticipated improvements to the reflectance-based method and their application and impact on the calibration of ASTER. These improvements should allow the absolute calibration of ASTER at the 3% level.
- Grotbeck, C. L., Santer, R. P., & Biggar, S. F. (1993). Solar aureole instrumentation and inversion techniques for aerosol studies: Part 1, system design and calibration. Proceedings of SPIE - The International Society for Optical Engineering, 1968, 556-565.More infoAbstract: The in-flight calibration of satellite radiometers using ground truth measurements relies on the use of an atmospheric radiative transfer code. The accuracy of the calibration depends largely on the aerosol model used in the radiative transfer codes. In order to improve the calibrations, a camera system has been developed for the determination of the aerosol size distribution, index of refraction, and scattering phase function. In addition, the camera can be used to measure ozone and water vapor content. The camera uses a two dimensional silicon CCD array to image the sun and the solar aureole. A filter wheel provides eight spectral bands from 310 nm to 1045 nm. The camera is mounted on an altitude-azimuth mount for tracking the sun. An external computer allows automatic or manual data acquisition. This paper presents the design and calibration of the camera system. A companion paper presents the data collection and inversion techniques used to retrieve the parameters of interest.
- Balick, L. K., Golanics, C. J., Shines, J. E., Biggar, S. F., & Slater, P. N. (1991). In-flight calibration of a helicopter-mounted Daedalus multispectral scanner. Proceedings of SPIE - The International Society for Optical Engineering, 1493, 215-223.More infoAbstract: A convenient technique that has been used to calibrate, in-flight, a helicopter-mounted Daedalus multispectral scanner is described. It used four large canvas panels laid out in a square with a Spectralon panel as a reference. A calibrated Barnes modular multispectral radiometer, carried on a 2.2-m boom, was rotated around a 2.5-m high tripod at the center of the square. The radiometer sampled the four large panels and the Spectralon panel once every two minutes. Atmospheric spectral transmittance measurements were made using a filter radiometer on an autotracking mount during the morning of the flight. The reflectance and optical depth data were used in an atmospheric radiative transfer code to predict the spectral radiances at the scanner. The calibration was completed by comparing the image digital counts to the predicted spectral radiances.
- Biggar, S. F., Dinguirard, M. C., Gellman, D. I., Henry, P., Jackson, R. D., Moran, M. S., & Slater, P. N. (1991). Radiometric calibration of SPOT 2 HRV: a comparison of three methods. Proceedings of SPIE - The International Society for Optical Engineering, 1493, 155-162.More infoAbstract: Three methods for determining an absolute radiometric calibration of a spacecraft optical sensor are compared. They are the well-known reflectance-based and radiance-based methods, and a new method based on measurements of the ratio of diffuse-to-global irradiance at the ground. The latter will be described in detail and the comparison of the three approaches will be made with reference to the SPOT-2 HRV cameras for a field campaign 1990-06-19 through 1990-06-24 at the White Sands Missile Range in New Mexico.
- Gellman, D. I., Biggar, S. F., Slater, P. N., & Bruegge, C. J. (1991). Calibrated intercepts for solar radiometers used in remote sensor calibration. Proceedings of SPIE - The International Society for Optical Engineering, 1493, 175-180.More infoAbstract: Calibrated solar radiometer intercepts allow spectral optical depths to be determined for days with intermittently clear skies. This is of particular importance on satellite sensor calibration days that are cloudy except at the time of image acquisition. This paper describes the calibration of four solar radiometers using the Langley-Bouguer technique for data collected on days with a clear, stable atmosphere. Intercepts are determined with an uncertainty of less than 6%, corresponding to a maximum uncertainty of 0.06 in optical depth. The spread of voltage intercepts calculated in this process is carried through three methods of radiometric calibration of satellite sensors to yield an uncertainty in radiance at the top of the atmosphere of less than 1% associated with the uncertainty in solar radiometer intercepts for a range of ground reflectances.
- Markham, B. L., Ahmad, S. P., Jackson, R. D., Moran, M. S., Biggar, S. F., Gellman, D. I., & Slater, P. N. (1991). Radiometric calibration of an airborne multispectral scanner. Proceedings of SPIE - The International Society for Optical Engineering, 1493, 207-214.More infoAbstract: The absolute radiometric calibration of the NS001 thematic mapper simulator reflective channels was examined based on laboratory tests and in-flight comparisons to ground measurements. The NS001 data are calibrated in-flight by reference to the NS001 internal integrating sphere source. This source's power supply or monitoring circuitry exhibited greater instability in-flight during 1988-1989 than in the laboratory. Extrapolating laboratory behavior to in-flight data resulted in 7-20% radiance errors relative to ground measurements and atmospheric modeling. Assuming constancy in the source's output between laboratory and in-flight resulted in generally smaller errors. Upgrades to the source's power supply and monitoring circuitry in 1990 improved its in-flight stability, though in-flight ground reflectance based calibration tests have not yet been performed.
- Nianzeng, C., Grant, B. G., Flittner, D. E., Slater, P. N., Biggar, S. F., Jackson, R. D., & Moran, M. S. (1991). Results of calibrations of the NOAA-11 AVHRR made by reference to calibrated SPOT imagery at White Sands, N.M.. Proceedings of SPIE - The International Society for Optical Engineering, 1493, 182-194.More infoAbstract: The calibration method reported here makes use of the reflectances of several large, uniform areas determined from calibrated and atmospherically corrected SPOT Haute Resolution Visible (HRV) scenes of White Sands, New Mexico. These reflectances were used to predict the radiances in the first two channels of the NOAA-11 Advanced Very High Resolution Radiometer (AVHRR). The digital counts in the AVHRR image corresponding to these known reflectance areas were determined by the use of two image registration techniques. The plots of digital counts versus pixel radiance provided the calibration gains and offsets for the AVHRR. A reduction in the gains of 4% and 13% in channels 1 and 2, respectively, was found during the period 19 November 1988 to 21 June 1990. An error budget is presented for the method and is extended to the case of cross-calibrating sensors on the same orbital platform in the Earth Observing System (EOS) era.
- Slater, P. N., Biggar, S. F., & Palmer, J. M. (1991). Ground-reference site and on-board methods for sensor absolute calibration in the 0.4 to 2.5 μm range. Digest - International Geoscience and Remote Sensing Symposium (IGARSS), 3, 1349-1351.More infoAbstract: The absolute radiometric calibration uncertainty requirement for several multispectral imaging sensors to be used in the Earth Observing System (EOS) program is ±2% (one sigma) with respect to the sun. The authors review some proposed in-flight absolute calibration methods that have this uncertainty as their goal. In particular, they describe two methods, and recent improvements to them, that concern reflectance- and radiance-based calibration using a carefully selected ground reference site. The magnitudes of the error sources are listed. A ratioing radiometer approach to monitoring the reflectance of a solar diffuser used for onboard calibration is discussed.
- Biggar, S. F., Gellman, D. I., & Slater, P. N. (1990). Improved evaluation of optical depth components from langley plot data. Remote Sensing of Environment, 32(2-3), 91-101.More infoAbstract: A simple, iterative procedure to determine the optical depth components of the extinction optical depth measured by a solar radiometer is presented. Simulated data show that the iterative procedure improves the determination of the exponent of a Junge law particle size distribution. The determination of the optical depth due to aerosol scattering is improved as compared to a method which uses only two points from the extinction data. The iterative method was used to determine spectral optical depth components for 11-13 June 1988 during the MAC III experiment. © 1990.
- Biggar, S. F., Santer, R. P., & Slater, P. N. (1990). Irradiance-based calibration of imaging sensors. Digest - International Geoscience and Remote Sensing Symposium (IGARSS), 507-510.More infoAbstract: A new method giving an absolute radiometric calibration of in-flight satellite or aircraft imaging optical sensors is presented. The method uses measurements of the global and diffuse irradiance at ground level, the ground reflectance, and spectral optical depths to derive a radiance at the sensor's entrance pupil. This radiance is compared with the sensor digital counts when it images the reflectance site to determine a calibration factor. The use of the irradiance values reduces the dependence on accurate knowledge of the size distribution of the aerosol particles responsible for scattering and allows the use of approximate codes instead of radiative transfer codes. The new irradiance-based method is compared with a reflectance-based calibration method which has been used to calibrate the Thematic Mapper on Landsat 4 and 5 and the HRV cameras on SPOT 1 and 2.
- Markham, B. L., Irons, J. R., Deering, D. W., Halthore, R. N., Irish, R. R., Jackson, R. D., Moran, M. S., Biggar, S. F., Gellman, D. I., Grant, B. G., Palmer, J. M., & Slater, P. N. (1990). Radiometric calibration of aircraft and satellite sensors at White Sands, NM. Digest - International Geoscience and Remote Sensing Symposium (IGARSS), 515-518.More infoAbstract: Multiple-angle data collected in November 1988 with the Advanced Solid-State Array Spectroradiometer (ASAS), an airborne pointable imaging spectrometer covering the 450-870-nm range, have been analyzed for two sites in the gypsum sand area of White Sands, NM. Comparison of the ASAS data to surface measurements suggests that in the central portion (550-750 nm) of the spectral coverage the radiometric calibration is good (±5%), but it is less accurate at shorter or longer wavelengths. Retrieved bidirectional reflectances (BRFs) in the principal plane of the sun (53° solar zenith angle (SZA)) showed variation in both the magnitude and shape of the BRF in the alkali flat areas. The effective principal plane BRF (54° SZA) of sand dune areas departed from that of flat dune sand, particularly at forward scatter angles, due to shadowing. Current results indicate that when using White Sands as a calibration site, laboratory bidirectional measurements of gypsum sand do not adequately describe field behavior. Also, extrapolation of field bidirectional data to areas not measured may not be warranted.
- Moran, M. S., Jackson, R. D., Hart, G. F., Slater, P. N., Bartell, R. J., Biggar, S. F., Gellman, D. I., & Santer, R. P. (1990). Obtaining surface reflectance factors from atmospheric and view angle corrected SPOT-1 HRV data. Remote Sensing of Environment, 32(2-3), 203-214.More infoAbstract: SPOT-1 High-Resolution Visible (HRV) multispectral (XS) and panchromatic data were acquired over an agricultural area on two consecutive days in June 1987, June 1988, and April 1989, at view zenith angles of approximately 23° and 10°. Digital data were converted to surface reflectance factors (ρs) by use of the sensor calibration coefficients, measurements of atmospheric optical depth, and a radiative transfer model. View-angle corrections (Cv) were derived from ground-based measurements of bidirectional radiance of bare soil, and used to convert nadir ground- and aircraft-based measurements to off-nadir values (ρg and ρa, respectively) for comparison with SPOT HRV data. The absolute error of ρs values, relative to ρg and ρa, was less than 10% for most XS bands on all six days over the reflectance range 0.1-0.4. However, there was a systematic trend for ρs estimates to be slightly higher than ρg and ρa measurements, particularly at low surface reflectances. The Cv coefficients were then applied to SPOT HRV data for a variety of cover types to assess the effectiveness of a simple, view-angle correction over a complex landscape. For rough, unvegetated surfaces, ρs values that had originally differed by more than 0.09 in reflectance on the two days were brought to within 0.01 in all three XS bands. For vegetated surfaces, Cv appeared to be wavelength dependent; the soil-based Cv worked well for data in the red and green wavebands but overcorrected the near-IR data. The Cv correction overcompensated for view angle effects over planar surfaces (i.e., water and roads) in all wavebands. © 1990.
- Holm, R. G., Jackson, R. D., Yuan, B., Moran, M. S., Slater, P. N., & Biggar, S. F. (1989). Surface reflectance factor retrieval from thematic mapper data. Remote Sensing of Environment, 27(1), 47-57.More infoAbstract: Based on the absolute radiometric calibration of the Thematic Mapper (TM) and the use of a radiative transfer program for atmospheric correction, ground reflectances were retrieved for several fields of crops and bare soil in TM Bands 1-4 for six TM scenes acquired over a 12-month period. These reflectances were compared to those measured using ground-based and low-altitude, aircraft-mounted radiometers. When, for four TM acquisitions, the comparison was made between areas that had been carefully selected for their high uniformity, the reflectance factors agreed to ±0.01 (1 σ RMS) over the reflectance range 0.02-0.55. When the comparison was made for two of the above acquisitions and two others on different dates, for larger areas not carefully selected to be of uniform reflectance, the reflectance factors agreed to ±0.02 (1 σ RMS), again over the reflectance range 0.02-0.55. © 1989.
- Jackson, R. D., Moran, M. S., Slater, P. N., & Biggar, S. F. (1987). Field calibration of reference reflectance panels. Remote Sensing of Environment, 22(1), 145-158.More infoAbstract: The measurement of radiation reflected from a surface must be accompanied by a near-simultaneous measurement of radiation reflected from a reference panel in order to calculate a bidirectional reflectance factor for the surface. Adequate calibration of the reference panel is necessary to assure valid reflectance-factor data. A procedure is described by which a reference panel can be calibrated with the sun as the irradiance source, with the component due to diffuse flux from the atmosphere subtracted from the total irradiance. Furthermore, the radiometer that is used for field measurements is also used as the calibration instrument. The reference panels are compared with a pressed polytetrafluoroethylene (halon) standard. The advantages of this procedure over conventional laboratory calibration methods are, first, that the irradiance and viewing geometry is the same as is used in field measurements and, second, that the needed equipment is available, or can be constructed, at most field research laboratories, including the press necessary to prepare the halon standard. A disadvantage of the method is that cloud-free sky conditions are required during the measurement period. The accuracy of the method is estimated to be 1%. Calibration results are given for four reference panels. © 1987.
- Slater, P. N., Biggar, S. F., Holm, R. G., Jackson, R. D., Mao, Y., Moran, M. S., Palmer, J. M., & Yuan, B. (1987). Reflectance- and radiance-based methods for the in-flight absolute calibration of multispectral sensors. Remote Sensing of Environment, 22(1), 11-37.More infoAbstract: Variations reported in the in-flight absolute radiometric calibration of the Coastal Zone Color Scanner (CZCS) and the Thematic Mapper (TM) on Landsat 4 are reviewed. At short wavelengths these sensors exhibited a gradual reduction in response, while in the midinfrared the TM showed oscillatory variations, according to the results of TM internal calibration. The methodology and results are presented for five reflectance-based calibrations of the Landsat 5 TM at White Sands, NM, in the period July 1984 to November 1985. These show a ±2.8% standard deviation (1 σ) for the six solar-reflective bands. Analysis and preliminary results of a second, independent calibration method based on radiance measurements from a helicopter at White Sands indicate that this is potentially an accurate method for corroborating the results from the reflectance-based method. © 1987.
- Slater, P. N., Biggar, S. F., Holm, R. G., Jackson, R. D., Mao, Y., Moran, M. S., Palmer, J. M., & Yuan, B. (1986). ABSOLUTE RADIOMETRIC CALIBRATION OF THE THEMATIC MAPPER.. Proceedings of SPIE - The International Society for Optical Engineering, 660, 2-8.More infoAbstract: The results are presented of five in-flight absolute radiometric calibrations, made in the period July 1984 to November 1985, at White Sands, New Mexico, of the solar reflective bands of the Landsat-5 Thematic Mapper (TM). The 23 band-calibrations made on the five dates show a plus or minus 2. 8% RMS variation from the mean as a percentage of the mean.