As an effective survey tool for oil spill detection, the airborne hyper-spectral sensor affords the potentiality for retrieving the quantitative information of oil slick which is useful for the cleanup of spilled oil. But many airborne hyper-spectral images are affected by sun glitter which distorts radiance values and spectral ratios used for oil slick detection. In 2005, there's an oil spill event leaking at oil drilling platform in The South China Sea, and an AISA+ airborne hyper-spectral image recorded this event will be selected for studying in this paper, which is affected by sun glitter terribly. Through a spectrum analysis of the oil and water samples, two features --"spectral rotation" and "a pair of fixed points" can be found in spectral curves between crude oil film and water. Base on these features, an oil film information retrieval method which can overcome the influence of sun glitter is presented. Firstly, the radiance of the image is converted to normal apparent reflectance (NormAR). Then, based on the features of "spectral rotation" (used for distinguishing oil film and water) and "a pair of fixed points" (used for overcoming the effect of sun glitter), NormAR 894 /NormAR 516 is selected as an indicator of oil film. Finally, by using a threshold combined with the technologies of image filter and mathematic morphology, the distribution and relative thickness of oil film are retrieved. INTRODUCEAs the development of economy, oil resources are more and more important for human. Followed, the oil spills in ocean from ships and oil platforms are increasing which have a serious influence to the marine environment. With remote sensing technology, several oil spill information such as distribution, thickness and type can be retrieved to help human clean oil film under scientific decisions.In oil spill remote sensing, thermal infrared camera, ultraviolet camera, microwave radiometer, multi-spectral scanners, synthetic aperture radar, laser fluorescence sensors have been used, but each of them has its own limitations [1] . With the widely use of the hyper-spectral technology, using hyper-spectral sensor to detect oil spills are constant attended by scholars. The hyper-spectral technology has great potential on the quantitative monitoring of oil distribution, type and quantity of spilled oil which effectively compensates the deficiencies of other sensors. *

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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 1 0% 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 .O43im, 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 ofthe same year, whose main sensor is for ocean color measurement, called as Chinese OceanColor and Temperature Scanner, COCTS, providing 8 visible and near-infrared channels similar to SeaWiFS21. 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.Here, for easy understanding the methodology and procedure of satellite cross-calibration, the CMODIS will be taken as an example to discuss. In principle, if two sensors measure the same target at the same observation condition, the measured radiance ofthe target by two sensors should be the same. So, one sensor which is unknown its accuracy in the orbit could be calibrated by another sensor with the higher accuracy one by the comparison of the radiance measured by two sensors respectively. The SeaWiFS accuracy ofradiance measurement is higher than 5 % (relative error) [3,4,5] so CMODIS is possible to be calibrated by SeaWiFS, even though these two sensors have their own observation geometric parameters which depend on the zenith of the sun and sensor, and azimuth between sensor and sun, supposed (e0,o,Aç) and (e() ,e, Aco)CMOI)IS for SeaWiFS and CMODIS observation geometries, respectively.First, the normalized water leaving radiance is possible to be calculated by SeaWiFS, and the type of aerosol can also be

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