Cross-Calibration of the MVIRS aboard the Chinese FY-1D against the MODIS aboard TERRA

摘要

The Multi-channel Visible Infrared Scanning radiometer (MVIRS) is a Chinese space-borne radiometer for weather and environmental monitoring. It has 6 channels equivalent to the current NOAA/AVHRR and 4 additional ones for remote sensing of ocean color and moisture. The MVIRS is currently in operation aboard a China’s polar-orbiting meteorological satellite (FY-1D) launched on May 15, 2002 with an overpass time slightly earlier than TERRA. The sensor has no on-board calibration assembly. This study attempts to calibrate MVIRS against the well-calibrated MODIS, by taking a series of measures to account for their differences. Clear-sky measurements made from the two sensors in July through October 2002 were first collocated over a Chinese calibration site in the Gobi desert. Using the 6S radiative transfer model, MODIS reflectance measured at the top of the atmosphere were converted into surface reflectance. They were corrected to the viewing geometry of the MVIRS using the bidirectional reflectance distribution function (BRDF) measured on the ground. The spectral response functions of the two sensors were employed to account for spectral discrepancies. After these corrections, very close linear correlations were found between radiances estimated from the MODIS and the digital readings from the MVIRS, from which the calibration gains were derived. The gains differ considerably from the pre- launch values and are subject to continual but gentle degradation over time. The calibration accuracy is estimated to be less than 5%, which is compatible to that obtained by the more expensive vicarious calibration approach.