Vicarious Calibration of the Formosat-2 Remote Sensing Instrument

We describe the results of the in-orbit radiometric calibration of the remote sensing instrument (RSI) onboard Formosat-2, based on the ground data collected by the advanced spaceborne thermal emission and reflection radiometer (ASTER) calibration team at Ivanpah Playa and Railroad Valley during the regular field campaigns in 2006 and 2008. These results are normalized by the preflight values provided by Astrium, France, and are compared with the results of in-flight calibrations made by Centre National d´Etudes Spatiales, France. The radiometric calibration coefficients and the long-term degrading trend of RSI are derived from the results of vicarious calibration, which estimate that the degradations of sensor sensitivity until 2008 are 2.2% (B4), 8.0% (B3), 9.6% (PAN), 10.3% (B2), and 12.0% (B1). Considering the fact that the ASTER calibration team is able to achieve an accuracy of vicarious calibration better than 5%, we estimate a 7.3% to 13.4% overestimate would be incurred by using the existing in-flight cross calibration coefficients to calculate the spectral radiances. This paper supports the use of vicarious calibration as a reliable approach for the in-orbit radiometric calibration of RSI onboard Formosat-2 on a regular basis.