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The one of the most important technique of satellite ocean color remote sensing is the radiance measurement accuracy because the water leaving radiance is only about 5% to 10% of the total radiance arrived at sensor at the satellite altitude. It is necessary to guarantee the accuracy of water leaving radiance measurement of about 5%(relative error) to meet the reversed accuracy of ocean color factors (such as chlorophyll suspended material and so on) within relative error about 30 in open sea (Case I water). When sensor has been in the orbit it is important to take orbit calibration to make up some deficits of the pre-launch calibration in the laboratory. Two kinds of data could be used for orbit calibration one is in-situ measurement date so-called in-situ field calibration and another is other satellite data with higher radiance measurement accuracy so called crossing-calibration. China has launched the third spaceship SZ-3 in March 2002. The main remote sensing sensor is the Chinese Moderate Imaging Spectroradiometer (CMODIS) which has total 34 channels (30 channels of 2Onm interval in the spectral range of 0.403-1.O43μm and four infrared channels with 2.15-2.25um, 8.4-8.5um, 10.3-11.3um and 11.5-12.5um. Following SZ-3 China had the first ocean color satellite HY-1A in May of the same year whose main sensor is for ocean color measurement, called as Chinese Ocean Color and Temperature Scanner, COCTS, providing 8 visible and near-infrared channels similar to SeaWiFS. In this paper, first, the methodology and procedure of satellite cross-calibration are discussed in detail, with taking an example of CMODIS. Then the results of this orbit cross-calibrated by American ocean sensor, Sea Wide Field-of-View Sensor (SeaWiFS), for CMODIS and COCTS are presented with comparing the normarization from pre-lunched Lab-calibration and in-situ measurement.
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