Cross-calibration of satellite sensors over snow fields

摘要

Besides pre-launch and on-board calibration, the method of vicariously calibrating space sensors became a reliable tool for space sensor calibration. One possibility of vicarious calibration is to inter-calibrate sensors aboard different satellite platforms directly. This leads to a better understanding of differences in global data sets produced these sensors. Recently, ADEOS-2 was launched (14 Dec 2002) successfully and the optical sensor GLI onboard the ADEOS-2 satellite became operational from April 2003. In a first calibration check-up, the radiometric performance of GLI was compared relatively to that of other sensors on different satellites with different calibration backgrounds. As calibration site a large snowfield near Barrow (Alaska, USA) was used, where space sensors in polar orbits view the same ground target on the same day with small differences in the local crossing times. This is why GLI, MODIS (terra, aqua), SeaWiFS, AHVRR (N16, N17) and MERIS data sets were selected for the following clear-sky condition days: April 14th and 26th 2003. At the same time ground-truth experiments, e.g., measurements of ground reflectance, BRDF, aerosol optical thickness (AOT), were carried out. Thereinafter, top-of- atmosphere (TOA) radiance/reflectance was forward calculated by means of radiative transfer code (RTC) for each sensor, each band and each day. Finally, the vicariously retrieved TOA reflectance was compared to TOA sensor L1B data. As a result GLI's performance is encouraging at this early time of the mission. GLI and the other 6 sensors deliver similar sensor output in the range of about 5-7 % around the expected vicariously calculated TOA signal.