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This paper aims to assess the relationship between the surface reflectance derived from ground based and aircraft measurements. The parameters of the Rahman–Pinty–Verstraete (RPV) and Ross Thick-LiSparse (RTLS) kernel based bi-directional reflectance distribution functions (BRDF), have been derived using actual measurements of the hemispherical-directional reflectance factor (HDRF), collected during different campaigns over the Railroad Valley Playa. The effect of the atmosphere, including that of the diffuse radiation on bi-directional reflectance factor (BRF) parameter retrievals, assessed using 6S model simulations, was negligible for the low turbidity conditions of the site under investigation (τ550≤0.05). It was also shown that the effects of the diffuse radiation on RPV spectral parameters retrieval is linear for the isotropic parameter ρ0 and the scattering parameter Θ, and can be described with a second order polynomial for the k-Minnaert parameter. In order to overcome the lack of temporal collocations between aircraft and in-situ measurements, Monte Carlo 3-D radiative transfer simulations mimicking in-situ and remote sensing techniques were performed on a synthetic parametric meshed scene defined by merging Landsat and Multianglhe Imaging Spectroradiometer (MISR) remote sensing reflectance data. We simulated directional reflectance measurements made at different heights for PARABOLA and CAR, and analyzed them according to practices adopted for real measurements, consisting of the inversion of BRF functions and the calculation of the bi-hemispherical reflectance (BHR). The difference of retrievals against the known benchmarks of kernel parameters and BHR is presented. We associated an uncertainty of up to 2% with the retrieval of area averaged BHR, independently of flight altitudes and the BRF model used for the inversion. As expected, the local nature of PARABOLA data is revealed by the difference of the anisotropic kernel parameters with the corresponding parameters retrieved from aircraft loops. The uncertainty of the resultant BHR fell within ±3%.
Christian Lanconelli; Andrew Banks; Jan-Peter Muller; Carol Bruegge; Fabrizio Cappucci; Charles Gatebe; Said Kharbouche; Olivier Morgan; Bernardo Mota; Nadine Gobron. In-Situ and Aircraft Reflectance Measurement Effectiveness for CAL/VAL Activities: A Study over Railroad Valley. Remote Sensing 2020, 12, 3366 .
AMA StyleChristian Lanconelli, Andrew Banks, Jan-Peter Muller, Carol Bruegge, Fabrizio Cappucci, Charles Gatebe, Said Kharbouche, Olivier Morgan, Bernardo Mota, Nadine Gobron. In-Situ and Aircraft Reflectance Measurement Effectiveness for CAL/VAL Activities: A Study over Railroad Valley. Remote Sensing. 2020; 12 (20):3366.
Chicago/Turabian StyleChristian Lanconelli; Andrew Banks; Jan-Peter Muller; Carol Bruegge; Fabrizio Cappucci; Charles Gatebe; Said Kharbouche; Olivier Morgan; Bernardo Mota; Nadine Gobron. 2020. "In-Situ and Aircraft Reflectance Measurement Effectiveness for CAL/VAL Activities: A Study over Railroad Valley." Remote Sensing 12, no. 20: 3366.
We present the results from Verification of Reference Irradiance and Radiance Sources Laboratory Calibration Experiment Campaign. Ten international laboratories took part in the measurements. The spectral irradiance comparison included the measurements of the 1000 W tungsten halogen filament lamps in the spectral range of 350 nm–900 nm in the pilot laboratory. The radiance comparison took a form of round robin where each participant in turn received two transfer radiometers and did the radiance calibration in their own laboratory. The transfer radiometers have seven spectral bands covering the wavelength range from 400 nm–700 nm. The irradiance comparison results showed an agreement between all lamps within ±1.5%. The radiance comparison results presented higher than expected discrepancies at the level of ±4%. Additional investigation to determine the causes for these discrepancies identified them as a combination of the size-of-source effect and instrument effective field of view that affected some of the results.
Agnieszka Białek; Teresa Goodman; Emma Woolliams; Johannes Brachmann; Thomas Schwarzmaier; Joel Kuusk; Ilmar Ansko; Viktor Vabson; Ian Lau; Christopher MacLellan; Sabine Marty; Michael Ondrusek; William Servantes; Sarah Taylor; Ronnie Van Dommelen; Andrew Barnard; Vincenzo Vellucci; Andrew Banks; Nigel Fox; Riho Vendt; Craig Donlon; Tânia Casal. Results from Verification of Reference Irradiance and Radiance Sources Laboratory Calibration Experiment Campaign. Remote Sensing 2020, 12, 2220 .
AMA StyleAgnieszka Białek, Teresa Goodman, Emma Woolliams, Johannes Brachmann, Thomas Schwarzmaier, Joel Kuusk, Ilmar Ansko, Viktor Vabson, Ian Lau, Christopher MacLellan, Sabine Marty, Michael Ondrusek, William Servantes, Sarah Taylor, Ronnie Van Dommelen, Andrew Barnard, Vincenzo Vellucci, Andrew Banks, Nigel Fox, Riho Vendt, Craig Donlon, Tânia Casal. Results from Verification of Reference Irradiance and Radiance Sources Laboratory Calibration Experiment Campaign. Remote Sensing. 2020; 12 (14):2220.
Chicago/Turabian StyleAgnieszka Białek; Teresa Goodman; Emma Woolliams; Johannes Brachmann; Thomas Schwarzmaier; Joel Kuusk; Ilmar Ansko; Viktor Vabson; Ian Lau; Christopher MacLellan; Sabine Marty; Michael Ondrusek; William Servantes; Sarah Taylor; Ronnie Van Dommelen; Andrew Barnard; Vincenzo Vellucci; Andrew Banks; Nigel Fox; Riho Vendt; Craig Donlon; Tânia Casal. 2020. "Results from Verification of Reference Irradiance and Radiance Sources Laboratory Calibration Experiment Campaign." Remote Sensing 12, no. 14: 2220.
Since recreational diving activities have increased in recent decades, resulting in additional environmental pressure on the coastal zone, the deployment of artificial reefs as a conservation strategy to divert mass ecotourism from fragile natural reefs has been proposed and realized in many areas of the world. Twelve units of a patented naturoid artificial reef technology developed by the Hellenic Centre for Marine Research (HCMR) were deployed in 2015 in the Underwater Biotechnological Park of Crete (UBPC) in order to create an experimental diving oasis and investigate the potential of achieving this aim for the over-exploited coastal ecosystems of this part of the Eastern Mediterranean. Assessment of the degree of establishment of artificial reefs and their ability to mimic natural ecosystems is often monitored through biological surveys and sampling. The measurement of the chemical, physical, and hydrodynamic characteristics of the water mass surrounding artificial reefs is also essential to fully understand their comparison to natural reefs. In particular, the flow field around reefs has been shown to be one of the most important physical factors in determining suitable conditions for the establishment of a number of key species on reef habitats. However, the combination of biological establishment monitoring and realistic flow-field simulation using computational fluid dynamics as a tool to aid in the design improvement of already existing reef installations has not been fully investigated in previous work. They are often reported separately as either ecological or engineering studies. Therefore, this study examined a full-scale numerical simulation of the field flow around individual already installed naturoid reef shapes, and part of their present arrangement on the sea bottom of the UPBC combined with the field-testing of the functionality of the installed artificial reefs concerning fish species aggregation. The results show that the simulated flow characteristics around the HCMR diving oasis artificial reefs were in good general agreement with the results of former studies, both for flows around a single deployed unit and for flows around a cluster of more than one unit. The results also gave good indications of the performance of individual reef units concerning key desirable characteristics such as downstream shadowing and sediment/nutrient upwelling and resuspension. In particular, they confirmed extended low flow levels (less than 0.3 m/s) and in some cases double vortexes on the downstream side of reef units where observed colonization and habitation of some key fish species had taken place. They also showed how the present distribution of units could be optimized to perform better as an integrated reef cluster. The use of computational fluid dynamics, with field survey data, is therefore suggested as a useful design improvement tool for installed reef structures and their deployment arrangement for recreational diving oases that can aid the sustainable development of the coastal zone.
Dimitrios Androulakis; Costas Dounas; Andrew Banks; Antonios Magoulas; Dionissios Margaris. An Assessment of Computational Fluid Dynamics as a Tool to Aid the Design of the HCMR-Artificial-ReefsTM Diving Oasis in the Underwater Biotechnological Park of Crete. Sustainability 2020, 12, 4847 .
AMA StyleDimitrios Androulakis, Costas Dounas, Andrew Banks, Antonios Magoulas, Dionissios Margaris. An Assessment of Computational Fluid Dynamics as a Tool to Aid the Design of the HCMR-Artificial-ReefsTM Diving Oasis in the Underwater Biotechnological Park of Crete. Sustainability. 2020; 12 (12):4847.
Chicago/Turabian StyleDimitrios Androulakis; Costas Dounas; Andrew Banks; Antonios Magoulas; Dionissios Margaris. 2020. "An Assessment of Computational Fluid Dynamics as a Tool to Aid the Design of the HCMR-Artificial-ReefsTM Diving Oasis in the Underwater Biotechnological Park of Crete." Sustainability 12, no. 12: 4847.
The European Copernicus programme ensures long-term delivery of high-quality, global satellite ocean colour radiometry (OCR) observations from its Sentinel-3 (S3) satellite series carrying the ocean and land colour instrument (OLCI). In particular, the S3/OLCI provides marine water leaving reflectance and derived products to the Copernicus marine environment monitoring service, CMEMS, for which data quality is of paramount importance. This is why OCR system vicarious calibration (OC-SVC), which allows uncertainties of these products to stay within required specifications, is crucial. The European organisation for the exploitation of meteorological satellites (EUMETSAT) operates the S3/OLCI marine ground segment, and envisions having an SVC infrastructure deployed and operated for the long-term. This paper describes a design for such an SVC infrastructure, named radiometry for ocean colour satellites calibration and community engagement (ROSACE), which has been submitted to Copernicus by a consortium made of three European research institutions, a National Metrology Institute, and two small- to medium-sized enterprises (SMEs). ROSACE proposes a 2-site infrastructure deployed in the Eastern and Western Mediterranean Seas, capable of delivering up to about 80 high quality matchups per year for OC-SVC of the S3/OLCI missions.
David Antoine; Vincenzo Vellucci; Andrew C. Banks; Philippe Bardey; Marine Bretagnon; Véronique Bruniquel; Alexis Deru; Odile Hembise Fanton D’Andon; Christophe Lerebourg; Antoine Mangin; Didier Crozel; Stéphane Victori; Alkiviadis Kalampokis; Aristomenis P. Karageorgis; George Petihakis; Stella Psarra; Melek Golbol; Edouard Leymarie; Agnieszka Bialek; Nigel Fox; Samuel Hunt; Joel Kuusk; Kaspars Laizans; Maria Kanakidou. ROSACE: A Proposed European Design for the Copernicus Ocean Colour System Vicarious Calibration Infrastructure. Remote Sensing 2020, 12, 1535 .
AMA StyleDavid Antoine, Vincenzo Vellucci, Andrew C. Banks, Philippe Bardey, Marine Bretagnon, Véronique Bruniquel, Alexis Deru, Odile Hembise Fanton D’Andon, Christophe Lerebourg, Antoine Mangin, Didier Crozel, Stéphane Victori, Alkiviadis Kalampokis, Aristomenis P. Karageorgis, George Petihakis, Stella Psarra, Melek Golbol, Edouard Leymarie, Agnieszka Bialek, Nigel Fox, Samuel Hunt, Joel Kuusk, Kaspars Laizans, Maria Kanakidou. ROSACE: A Proposed European Design for the Copernicus Ocean Colour System Vicarious Calibration Infrastructure. Remote Sensing. 2020; 12 (10):1535.
Chicago/Turabian StyleDavid Antoine; Vincenzo Vellucci; Andrew C. Banks; Philippe Bardey; Marine Bretagnon; Véronique Bruniquel; Alexis Deru; Odile Hembise Fanton D’Andon; Christophe Lerebourg; Antoine Mangin; Didier Crozel; Stéphane Victori; Alkiviadis Kalampokis; Aristomenis P. Karageorgis; George Petihakis; Stella Psarra; Melek Golbol; Edouard Leymarie; Agnieszka Bialek; Nigel Fox; Samuel Hunt; Joel Kuusk; Kaspars Laizans; Maria Kanakidou. 2020. "ROSACE: A Proposed European Design for the Copernicus Ocean Colour System Vicarious Calibration Infrastructure." Remote Sensing 12, no. 10: 1535.
Earth observation data can help us understand and address some of the grand challenges and threats facing us today as a species and as a planet, for example climate change and its impacts and sustainable use of the Earth’s resources. However, in order to have confidence in earth observation data, measurements made at the surface of the Earth, with the intention of providing verification or validation of satellite-mounted sensor measurements, should be trustworthy and at least of the same high quality as those taken with the satellite sensors themselves. Metrology tells us that in order to be trustworthy, measurements should include an unbroken chain of SI-traceable calibrations and comparisons and full uncertainty budgets for each of the in situ sensors. Until now, this has not been the case for most satellite validation measurements. Therefore, within this context, the European Space Agency (ESA) funded a series of Fiducial Reference Measurements (FRM) projects targeting the validation of satellite data products of the atmosphere, land, and ocean, and setting the framework, standards, and protocols for future satellite validation efforts. The FRM4SOC project was structured to provide this support for evaluating and improving the state of the art in ocean colour radiometry (OCR) and satellite ocean colour validation through a series of comparisons under the auspices of the Committee on Earth Observation Satellites (CEOS). This followed the recommendations from the International Ocean Colour Coordinating Group’s white paper and supports the CEOS ocean colour virtual constellation. The main objective was to establish and maintain SI traceable ground-based FRM for satellite ocean colour and thus make a fundamental contribution to the European system for monitoring the Earth (Copernicus). This paper outlines the FRM4SOC project structure, objectives and methodology and highlights the main results and achievements of the project: (1) An international SI-traceable comparison of irradiance and radiance sources used for OCR calibration that set measurement, calibration and uncertainty estimation protocols and indicated good agreement between the participating calibration laboratories from around the world; (2) An international SI-traceable laboratory and outdoor comparison of radiometers used for satellite ocean colour validation that set OCR calibration and comparison protocols; (3) A major review and update to the protocols for taking irradiance and radiance field measurements for satellite ocean colour validation, with particular focus on aspects of data acquisition and processing that must be considered in the estimation of measurement uncertainty and guidelines for good practice; (4) A technical comparison of the main radiometers used globally for satellite ocean colour validation bringing radiometer manufacturers together around the same table for the first time to discuss instrument characterisation and its documentation, as needed for measurement uncertainty estimation; (5) Two major international side-by-side field intercomparisons of multiple ocean colour radiometers, one on the Atlantic Meridional Transect (AMT) oceanographic cruise, and the other on the Acqua Alta oceanographic tower in the Gulf of Venice; (6) Impact and promotion of FRM within the ocean colour community, including a scientific road map for the FRM-based future of satellite ocean colour validation and vicarious calibration (based on the findings of the FRM4SOC project, the consensus from two major international FRM4SOC workshops and previous literature, including the IOCCG white paper on in situ ocean colour radiometry).
Andrew Clive Banks; Riho Vendt; Krista Alikas; Agnieszka Bialek; Joel Kuusk; Christophe Lerebourg; Kevin Ruddick; Gavin Tilstone; Viktor Vabson; Craig Donlon; Tania Casal. Fiducial Reference Measurements for Satellite Ocean Colour (FRM4SOC). Remote Sensing 2020, 12, 1322 .
AMA StyleAndrew Clive Banks, Riho Vendt, Krista Alikas, Agnieszka Bialek, Joel Kuusk, Christophe Lerebourg, Kevin Ruddick, Gavin Tilstone, Viktor Vabson, Craig Donlon, Tania Casal. Fiducial Reference Measurements for Satellite Ocean Colour (FRM4SOC). Remote Sensing. 2020; 12 (8):1322.
Chicago/Turabian StyleAndrew Clive Banks; Riho Vendt; Krista Alikas; Agnieszka Bialek; Joel Kuusk; Christophe Lerebourg; Kevin Ruddick; Gavin Tilstone; Viktor Vabson; Craig Donlon; Tania Casal. 2020. "Fiducial Reference Measurements for Satellite Ocean Colour (FRM4SOC)." Remote Sensing 12, no. 8: 1322.
The coastal ocean is one of the most important environments on our planet, home to some of the most bio-diverse and productive ecosystems and providing key input to the livelihood of the majority of human society. It is also a highly dynamic and sensitive environment, particularly susceptible to damage from anthropogenic influences such as pollution and over-exploitation as well as the effects of climate change. These have the added potential to exacerbate other anthropogenic effects and the recent change in sea temperature can be considered as the most pervasive and severe cause of impact in coastal ecosystems worldwide. In addition to open ocean measurements, satellite observations of sea surface temperature (SST) have the potential to provide accurate synoptic coverage of this essential climate variable for the near-shore coastal ocean. However, this potential has not been fully realized, mainly because of a lack of reliable in situ validation data, and the contamination of near-shore measurements by the land. The underwater biotechnological park of Crete (UBPC) has been taking near surface temperature readings autonomously since 2014. Therefore, this study investigated the potential for this infrastructure to be used to validate SST measurements of the near-shore coastal ocean. A comparison between in situ data and Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Terra SST data is presented for a four year (2014–2018) in situ time series recorded from the UBPC. For matchups between in situ and satellite SST data, only nighttime in situ extrapolated to the sea surface (SSTskin) data within ±1 h from the satellite’s overpass are selected and averaged. A close correlation between the in situ data and the MODIS SST was found (squared Pearson correlation coefficient-r2 > 0.9689, mean absolute error-Δ < 0.51 both for Aqua and Terra products). Moreover, close correlation was found between the satellite data and their adjacent satellite pixel’s data further from the shore (r2 > 0.9945, Δ < 0.23 for both Aqua and Terra products, daytime and nighttime satellite SST). However, there was also a consistent positive systematic difference in the satellite against satellite mean biases indicating a thermal adjacency effect from the land (e.g., mean bias between daytime Aqua satellite SST from the UBPC cell minus the respective adjacent cell’s data is δ = 0.02). Nevertheless, if improvements are made in the in situ sensors and their calibration and uncertainty evaluation, these initial results indicate that near-shore autonomous coastal underwater temperature arrays, such as the one at UBPC, could in the future provide valuable in situ data for the validation of satellite coastal SST measurements.
Dimitrios N. Androulakis; Andrew Clive Banks; Costas Dounas; Dionissios P. Margaris. An Evaluation of Autonomous In Situ Temperature Loggers in a Coastal Region of the Eastern Mediterranean Sea for Use in the Validation of Near-Shore Satellite Sea Surface Temperature Measurements. Remote Sensing 2020, 12, 1140 .
AMA StyleDimitrios N. Androulakis, Andrew Clive Banks, Costas Dounas, Dionissios P. Margaris. An Evaluation of Autonomous In Situ Temperature Loggers in a Coastal Region of the Eastern Mediterranean Sea for Use in the Validation of Near-Shore Satellite Sea Surface Temperature Measurements. Remote Sensing. 2020; 12 (7):1140.
Chicago/Turabian StyleDimitrios N. Androulakis; Andrew Clive Banks; Costas Dounas; Dionissios P. Margaris. 2020. "An Evaluation of Autonomous In Situ Temperature Loggers in a Coastal Region of the Eastern Mediterranean Sea for Use in the Validation of Near-Shore Satellite Sea Surface Temperature Measurements." Remote Sensing 12, no. 7: 1140.
This paper reviews the state of the art of protocols for the measurement of downwelling irradiance in the context of Fiducial Reference Measurements (FRM) of water reflectance for satellite validation. The measurement of water reflectance requires the measurement of water-leaving radiance and downwelling irradiance just above water. For the latter, there are four generic families of method, using: (1) an above-water upward-pointing irradiance sensor; (2) an above-water downward-pointing radiance sensor and a reflective plaque; (3) a Sun-pointing radiance sensor (sunphotometer); or (4) an underwater upward-pointing irradiance sensor deployed at different depths. Each method—except for the fourth, which is considered obsolete for the measurement of above-water downwelling irradiance—is described generically in the FRM context with reference to the measurement equation, documented implementations, and the intra-method diversity of deployment platform and practice. Ideal measurement conditions are stated, practical recommendations are provided on best practice, and guidelines for estimating the measurement uncertainty are provided for each protocol-related component of the measurement uncertainty budget. The state of the art for the measurement of downwelling irradiance is summarized, future perspectives are outlined, and key debates such as the use of reflectance plaques with calibrated or uncalibrated radiometers are presented. This review is based on the practice and studies of the aquatic optics community and the validation of water reflectance, but is also relevant to land radiation monitoring and the validation of satellite-derived land surface reflectance.
Kevin G. Ruddick; Kenneth Voss; Andrew C. Banks; Emmanuel Boss; Alexandre Castagna; Robert Frouin; Martin Hieronymi; Cedric Jamet; B. Carol Johnson; Joel Kuusk; Zhongping Lee; Michael Ondrusek; Viktor Vabson; Riho Vendt. A Review of Protocols for Fiducial Reference Measurements of Downwelling Irradiance for the Validation of Satellite Remote Sensing Data over Water. Remote Sensing 2019, 11, 1742 .
AMA StyleKevin G. Ruddick, Kenneth Voss, Andrew C. Banks, Emmanuel Boss, Alexandre Castagna, Robert Frouin, Martin Hieronymi, Cedric Jamet, B. Carol Johnson, Joel Kuusk, Zhongping Lee, Michael Ondrusek, Viktor Vabson, Riho Vendt. A Review of Protocols for Fiducial Reference Measurements of Downwelling Irradiance for the Validation of Satellite Remote Sensing Data over Water. Remote Sensing. 2019; 11 (15):1742.
Chicago/Turabian StyleKevin G. Ruddick; Kenneth Voss; Andrew C. Banks; Emmanuel Boss; Alexandre Castagna; Robert Frouin; Martin Hieronymi; Cedric Jamet; B. Carol Johnson; Joel Kuusk; Zhongping Lee; Michael Ondrusek; Viktor Vabson; Riho Vendt. 2019. "A Review of Protocols for Fiducial Reference Measurements of Downwelling Irradiance for the Validation of Satellite Remote Sensing Data over Water." Remote Sensing 11, no. 15: 1742.
CAR (Cloud Absorption Radiometer) is a multi-angular and multi-spectral airborne radiometer instrument, whose radiometric and geometric characteristics are well calibrated and adjusted before and after each flight campaign. CAR was built by NASA (National Aeronautics and Space Administration) in 1984. On 16 May 2008, a CAR flight campaign took place over the well-known calibration and validation site of Railroad Valley in Nevada, USA (38.504°N, 115.692°W). The campaign coincided with the overpasses of several key EO (Earth Observation) satellites such as Landsat-7, Envisat and Terra. Thus, there are nearly simultaneous measurements from these satellites and the CAR airborne sensor over the same calibration site. The CAR spectral bands are close to those of most EO satellites. CAR has the ability to cover the whole range of azimuth view angles and a variety of zenith angles depending on altitude and, as a consequence, the biases seen between satellite and CAR measurements due to both unmatched spectral bands and unmatched angles can be significantly reduced. A comparison is presented here between CAR’s land surface reflectance (BRF or Bidirectional Reflectance Factor) with those derived from Terra/MODIS (MOD09 and MAIAC), Terra/MISR, Envisat/MERIS and Landsat-7. In this study, we utilized CAR data from low altitude flights (approx. 180 m above the surface) in order to minimize the effects of the atmosphere on these measurements and then obtain a valuable ground-truth data set of surface reflectance. Furthermore, this study shows that differences between measurements caused by surface heterogeneity can be tolerated, thanks to the high homogeneity of the study site on the one hand, and on the other hand, to the spatial sampling and the large number of CAR samples. These results demonstrate that satellite BRF measurements over this site are in good agreement with CAR with variable biases across different spectral bands. This is most likely due to residual aerosol effects in the EO derived reflectances.
Said Kharbouche; Jan-Peter Muller; Charles K. Gatebe; Tracy Scanlon; Andrew C. Banks. Assessment of Satellite-Derived Surface Reflectances by NASA’s CAR Airborne Radiometer over Railroad Valley Playa. Remote Sensing 2017, 9, 562 .
AMA StyleSaid Kharbouche, Jan-Peter Muller, Charles K. Gatebe, Tracy Scanlon, Andrew C. Banks. Assessment of Satellite-Derived Surface Reflectances by NASA’s CAR Airborne Radiometer over Railroad Valley Playa. Remote Sensing. 2017; 9 (6):562.
Chicago/Turabian StyleSaid Kharbouche; Jan-Peter Muller; Charles K. Gatebe; Tracy Scanlon; Andrew C. Banks. 2017. "Assessment of Satellite-Derived Surface Reflectances by NASA’s CAR Airborne Radiometer over Railroad Valley Playa." Remote Sensing 9, no. 6: 562.