Abstract
An empirical model of expected top-of-atmosphere reflectances over the Libya-4 pseudo invariant calibration site is developed by using archived Maxar imagery taken over the site between 2014 and 2021 for absolute radiometric calibration of VNIR and SWIR Earth observing sensors. For this model 212 WorldView-3 VNIR, 211 WorldView-3 SWIR, 252 WorldView-2, and 113 GeoEye-1 images were used. The images are calibrated using results from reflectance-based vicarious calibration efforts over specialized tarps at Maxar’s Ft. Lupton calibration facility. The sensor multispectral data are then transformed to hyperspectral data with the aid of NASA EO-1 Hyperion imagery over the same site and then model coefficients are derived using a Rahman-Pinty-Verstraete fit. Hyperspecial outputs of top-of-atmosphere reflectance from this model are run at relevant image acquisition times and solar and sensor view angles; and the resulting truth data are band averaged to the sensor under test. Results using WorldView-4 as the test sensor are validated over the Radiometric Calibration Network (RadCalNet) site at Railroad Valley, NV, USA (RVUS) and found to match within +/- 3%. RadCalNet is an initiative of the Working Group on Calibration and Validation of the Committee on Earth Observation Satellites that provides SI-traceable top-of-atmosphere reflectances for post-launch radiometric calibration and validation of optical imaging sensor data. The Libya-4 site is known to change within 2-3% temporally and the reflectance-based method has a known uncertainty of less than 3%. This method can be used for sensors that have a larger ground sample distance or pixel size than can be accommodated on Maxar’s 20 x 30 m calibration tarps. It can also be used for the initial calibration of sensors launched during the winter months, when the Maxar calibration facility is not available due to weather.
Transfer of Reflectance-Based Absolute Radiometric Calibration of GE01, WV02 and WV03 to WV04 using the Libya-4 Pseudo Invariant Calibration Site in an Empirical Top-of-Atmosphere Reflectance Model
An empirical model of expected top-of-atmosphere reflectances over the Libya-4 pseudo invariant calibration site is developed by using archived Maxar imagery taken over the site between 2014 and 2021 for absolute radiometric calibration of VNIR and SWIR Earth observing sensors. For this model 212 WorldView-3 VNIR, 211 WorldView-3 SWIR, 252 WorldView-2, and 113 GeoEye-1 images were used. The images are calibrated using results from reflectance-based vicarious calibration efforts over specialized tarps at Maxar’s Ft. Lupton calibration facility. The sensor multispectral data are then transformed to hyperspectral data with the aid of NASA EO-1 Hyperion imagery over the same site and then model coefficients are derived using a Rahman-Pinty-Verstraete fit. Hyperspecial outputs of top-of-atmosphere reflectance from this model are run at relevant image acquisition times and solar and sensor view angles; and the resulting truth data are band averaged to the sensor under test. Results using WorldView-4 as the test sensor are validated over the Radiometric Calibration Network (RadCalNet) site at Railroad Valley, NV, USA (RVUS) and found to match within +/- 3%. RadCalNet is an initiative of the Working Group on Calibration and Validation of the Committee on Earth Observation Satellites that provides SI-traceable top-of-atmosphere reflectances for post-launch radiometric calibration and validation of optical imaging sensor data. The Libya-4 site is known to change within 2-3% temporally and the reflectance-based method has a known uncertainty of less than 3%. This method can be used for sensors that have a larger ground sample distance or pixel size than can be accommodated on Maxar’s 20 x 30 m calibration tarps. It can also be used for the initial calibration of sensors launched during the winter months, when the Maxar calibration facility is not available due to weather.