Directional Reflectance Studies in Support of the Radiometric Calibration Test Site (RadCaTS) at Railroad Valley

The Radiometric Calibration Test Site (RadCaTS) is a suite of commercial and custom instruments used to make measurements of the surface reflectance and atmosphere throughout the day at Railroad Valley, Nevada. It was developed in response to the need for daily radiometric calibration data for the vast array of Earth-observing sensors on orbit, which is continuously increasing as more nations and private companies launch individual environmental satellites as well as large constellations. The current suite of instruments at RadCaTS includes five ground-viewing radiometers (GVRs), four of which view the surface in a nadir-viewing configuration. Many sensors such as those on Landsat-7 and Landsat-8 view Railroad Valley within 3 of nadir, while others such as those on Sentinel-2A and -2B, RapidEye, Aqua, Suomi NPP, and Terra can view Railroad Valley at off-nadir angles. Past efforts have shown that the surface bidirectional reflectance distribution function (BRDF) has minimal impact on vicarious calibration uncertainties for views <10, but the desire to use larger view angles has prompted the effort to develop a BRDF correction for data from RadCaTS. The current work investigates the application of Railroad Valley BRDF data derived from a BRF camera developed at the University of Arizona in the 1990s (but is no longer in use) to the current RadCaTS surface reflectance measurements. Also investigated are early results from directional reflectance studies using a mobile spectro-goniometer system during a round-robin field campaign in 2018. This work describes the preliminary results, the effects on current measurements, and the approach for future measurements

Landsat-7 ETM+ Radiometric Calibration Status

Now in its 17th year of operation, the Enhanced Thematic Mapper + (ETM+), on board the Landsat-7 satellite, continues to systematically acquire imagery of the Earth to add to the 40+ year archive of Landsat data. Characterization of the ETM+ on-orbit radiometric performance has been on-going since its launch in 1999. The radiometric calibration of the reflective bands is still monitored using on-board calibration devices, though the Pseudo-Invariant Calibration Sites (PICS) method has proven to be an effect tool as well. The calibration gains were updated in April 2013 based primarily on PICS results, which corrected for a change of as much as -0.2%/year degradation in the worst case bands. A new comparison with the SADE database of PICS results indicates no additional degradation in the updated calibration. PICS data are still being tracked though the recent trends are not well understood. The thermal band calibration was updated last in October 2013 based on a continued calibration effort by NASA/Jet Propulsion Lab and Rochester Institute of Technology. The update accounted for a 0.31 W/sq m/ sr/micron bias error. The updated lifetime trend is now stable to within + 0.4K

Analysis of a commercial small unmanned airborne system (sUAS) in support of the Radiometric Calibration Test Site (RadCaTS) at Railroad Valley

The Radiometric Calibration Test Site (RadCaTS) is an automated facility developed by the Remote Sensing Group (RSG) at the University of Arizona to provide radiometric calibration data for airborne and satellite sensors. RadCaTS uses stationary ground-viewing radiometers (GVRs) to spatially sample the surface reflectance of the site. The number and location of the GVRs is based on previous spatial, spectral, and temporal analyses of Railroad Valley. With the increase in high-resolution satellite sensors, there is renewed interest in examining the spatial uniformity the 1-km(2) RadCaTS area at scales smaller than a typical 30-m sensor. RadCaTS is one of the four instrumented sites currently in the CEOS WGCV Radiometric Calibration Network (RadCalNet), which aims to harmonize the post-launch radiometric calibration of satellite sensors through the use of a global network of automated calibration sites. A better understanding of the RadCaTS spatial uniformity as a function of pixel size will also benefit the RadCalNet work. RSG has recently acquired a commercially-available small unmanned airborne system (sUAS) system, with which preliminary spatial homogeneity measurements of the 1-km2 RadCaTS area were made. This work describes an initial assessment of the airborne platform and integrated camera for spatial studies of RadCaTS using data that were collected in 2016 and 2017.NASAThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Intercomparison of the GOES-16 and -17 Advanced Baseline Imager with low-Earth orbit sensors

The GOES-16 satellite was launched on 19 Nov 2016, and it became operational as the GOES-East satellite on 18 Dec 2017. The GOES-17 satellite was launched on 1 Mar 2018, and it became the GOES-West operational satellite on 12 Feb 2019. The Advanced Baseline Imager (ABI) is one of six instruments onboard GOES-16 and -17. ABI has 16 spectral bands, a spatial resolution of 0.5 km to 2.0 km, and five times the temporal coverage of the previous GOES Imager series of sensors. The Radiometric Calibration Test Site (RadCaTS) is an automated facility at Railroad Valley, Nevada, USA, which contains ground based instruments that measure the surface reflectance and atmosphere throughout the day. It was developed by the Remote Sensing Group (RSG) of the James C. Wyant College of Optical Sciences at the University of Arizona, and it is currently used to monitor such low Earth orbit (LEO) sensors as Landsat-7 ETM+, Landsat-8 OLI, Terra and Aqua MODIS, Sentinel-2A and -2B MSI, Sentinel-3A and -3B OLCI and SLSTR, and others. The improved spectral, spatial, and temporal characteristics of ABI create an excellent opportunity to intercompare results obtained from a geosynchronous sensor to those obtained from typical LEO sensors. This work describes current efforts to validate the radiometric calibration of ABI as well as perform an intercomparison with various LEO sensors.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Calibration and use of an ultra-portable field transfer radiometer for automated vicarious calibration

A small portable transfer radiometer has been developed as part of an effort to ensure the quality of upwelling radiance at automated test sites used for vicarious calibration in the solar reflective. The test sites, such as the one located at Railroad Valley, are used to predict top-of-atmosphere reflectance relying on ground-based measurements of the atmosphere and surface. The portable transfer radiometer is designed for one-person operation for on-site field calibration the instrumentation used to determine ground-leaving radiance. The current work describes the laboratory-based calibration of the transfer radiometer highlighting the expected accuracy and SI-traceability. Results from recent field deployments of the transfer radiometer are presented to show how the sensor is to be used for 1) evaluating the health of the automated site radiometers, 2) characterizing the surface being measured at the automated test sites, and 3) assessing the error budget for top-of-atmosphere reflectance prediction the test site characterization. Additionally, results from using the transfer radiometer for a radiance-based calibration of the Operational Land Imager are presented.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Radiometric Degradation Curves for the ASTER VNIR Processing Using Vicarious and Lunar Calibrations

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard Terra platform, which was launched in 1999, has three separate subsystems: a visible and near-infrared (VNIR) radiometer, a shortwave-infrared radiometer, and a thermal-infrared radiometer. The ASTER VNIR bands have been radiometrically corrected for approximately 14 years by the sensor degradation curves estimated from the onboard calibrator according to the original calibration plan. However, this calibration by the onboard calibrator encountered a problem; specifically, it is inconsistent with the results of vicarious calibration and cross calibration. Therefore, the ASTER VNIR processing was applied by the radiometric degradation curves calculated from the results of three calibration approaches, i.e., the onboard calibrator, the vicarious calibration, and the cross calibration since February 2014. Even though the current degradation curves were revised, the inter-band and lunar calibrations show some inconsistencies owing to the different traceability in the bands by different calibration approaches. In this study, the current degradation curves and their problems are explained, and the new curves that are derived from the vicarious calibration with lunar calibration are discussed. The new degradation curves that have the same traceability in the bands will be used for future ASTER VNIR processing.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]