Ultra-Portable Field Transfer Radiometer for Vicarious Calibration of Earth Imaging Sensors

A small portable transfer radiometer has been developed as part of an effort to ensure the quality of upwelling radiance from test sites used for vicarious calibration in the solar reflective. The test sites 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 of instrumentation used to determine ground-leaving radiance. The current work describes the detector-and source-based radiometric calibration of the transfer radiometer highlighting the expected accuracy and SI-traceability. The results indicate differences between the detector-based and source-based results greater than the combined uncertainties of the approaches. Results from recent field deployments of the transfer radiometer using a solar radiation based calibration agree with the source-based laboratory calibration within the combined uncertainties of the methods. The detector-based results show a significant difference to the solar-based calibration. The source-based calibration is used as the basis for a radiance-based calibration of the Landsat-8 Operational Land Imager that agrees with the OLI calibration to within the uncertainties of the methods

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

Automated Ground-Based Methodology in Support of Vicarious Calibration

The Remote Sensing Group (RSG) at the University of Arizona performs the vicarious calibration of airborne and spaceborne sensors using ground-based measurements. Vicarious calibration is important because it is independent of the sensor and any onboard calibration system, but it requires that RSG personnel be present at a test site during the aircraft or satellite overpass. The ground-based data collection can be limited by poor weather, and also by the large travel distances from RSG's laboratory to the test sites.This dissertation presents an automated methodology that is used in support of vicarious calibration. The most important parameter measured during a vicarious calibration field campaign is the surface reflectance, and this work describes the method and instrumentation to obtain surface reflectance in the absence of RSG personnel. The instrumentation required to measure the surface and atmospheric parameters is discussed. The design and laboratory characterization of a nadir-viewing, multispectral radiometer is presented. Finally, results using this methodology are compared to those obtained using vicarious calibration, and also with the top-of-atmosphere radiance for one Terra MODIS, and two Aqua MODIS overpasses

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]

Earth-observing Satellite Intercomparison Using the Radiometric Calibration Test Site at Railroad Valley

This paper describes the current ground-based calibration results of Landsat 7 Enhanced Thematic Mapper Plus (ETM+), Landsat 8 Operational Land Imager (OLI), Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS), Suomi National Polar orbiting Partnership Visible Infrared Imaging Radiometer Suite (VIIRS), and Sentinel-2A Multispectral Instrument (MSI), using an automated suite of instruments located at Railroad Valley, Nevada, USA. The period of this study is 2012 to 2016 for MODIS, VIIRS, and ETM+, 2013 to 2016 for OLI, and 2015 to 2016 for MSI. The current results show that all sensors agree with the Radiometric Calibration Test Site (RadCaTS) to within +/-5% in the solar-reflective regime, except for one band on VIIRS that is within +/-6%. In the case of ETM+ and OLI, the agreement is within +/-3%, and, in the case of MODIS, the agreement is within +/-3.5%. MSI agrees with RadCaTS to within +/-4.5% in all applicable bands

Railroad Valley Radiometric Calibration Test Site (RadCaTS) as Part of a Global Radiometric Calibration Network (RadCalNet)

The Radiometric Calibration Network (RadCalNet) is a coordinated multinational effort to provide in situ data that are suitable for the radiometric calibration and validation of Earth observation sensors that operate in the visible to shortwave infrared solar reflective spectral region (400 nm to 1000 nm). The main goals of RadCalNet are to provide top-of-atmosphere reflectance data to the scientific community, standardize data collection protocols for automated test sites, and to document the SI-traceable uncertainty budgets for each automated test site, of which there are currently four. The data available from RadCalNet are suitable for the calibration and validation of spaceborne imaging spectrometers. The work presented here provides a description of RadCalNet as well as a sample of the current results from the Radiometric Calibration Test Site (RadCaTS), which is located at Railroad Valley, Nevada, USA. Selected sensors for comparison include Terra and Aqua MODIS, SNPP and NOAA-20 VIIRS, and Sentinel-3A and −3B OLCI.National Aeronautics and Space AdministrationThis 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]

Earth-observing satellite intercomparison using the Radiometric Calibration Test Site at Railroad Valley

This paper describes the current ground-based calibration results of Landsat 7 Enhanced Thematic Mapper Plus (ETM+), Landsat 8 Operational Land Imager (OLI), Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS), Suomi National Polar orbiting Partnership Visible Infrared Imaging Radiometer Suite (VIIRS), and Sentinel-2A Multispectral Instrument (MSI), using an automated suite of instruments located at Railroad Valley, Nevada, USA. The period of this study is 2012 to 2016 for MODIS, VIIRS, and ETM+, 2013 to 2016 for OLI, and 2015 to 2016 for MSI. The current results show that all sensors agree with the Radiometric Calibration Test Site (RadCaTS) to within +/- 5% in the solar-reflective regime, except for one band on VIIRS that is within +/- 6%. In the case of ETM+ and OLI, the agreement is within +/- 3%, and, in the case of MODIS, the agreement is within +/- 3.5%. MSI agrees with RadCaTS to within +/- 4.5% in all applicable bands. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.NASA research Grant [NNX14AJ19G, NNX14AP68A, NNX16AH44G]; USGS [G14AC00371]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]