Directional reflectance studies in support of the Radiometric Calibration Test Site (RadCaTS) at Railroad Valley

Abstract

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.

Vicarious calibration correction of large FOV sensor using BRDF model based on UAV angular spectrum measurements

“…22,23 During the field calibration campaign in 2018, directional reflectance studies using a mobile spectro-goniometer system-the University of Lethbridge Goniometer System developed by the University of Lethbridge 24 -together with the BRF camera were employed to obtain the BRDF data for MODIS calibration correction, improving accuracy by 3% compared to the onboard calibration coefficient. 25 China has launched several series of land observation satellites, including the CBERS, HJ, GF, and ZY. Each year a calibration campaign is carried out at the Dunhuang calibration site for the visible and near-infrared sensors of China's land observation satellites using the reflectancebased method.…”