Application Of CALIOP In MODIS-based Sea Fog Detection

Using the satellite remote sensing technology to detect the sea-fog is the primarymethod, but the result is difficult to be verified because of the lack of obsevaions onthe ocean. The CALIOP equipped on the CALIPSO uses an active lidar instrument toprobe the vertical structure of the atmosphere at high-resolution. The CALIOP can beused to classify the observed objects into sea-surface, sea-fog, low-cloud,middle-cloud/high-cloud. Collocated Aqua-MODIS data and CALIOP data can beused together to get multiple calssified object samples and get their spectralproperities. Through the spectral properities statistics the thresholds used for the fogdetection can be set. Except the threshold, the CALIOP can be used to verify themethod used to calculate the sea-fog thickness and annlyze the applicability ofMODIS-based sea-fog ditection.1146day-fog samples and1085night-fog samples are classified by CALIOP andthe statistics of their spectral perosperites from Aqua-MODIS are presented. Theresults show that:1. for daytime, from MODIS channel1, channel2,85%of albedo of sea-fog isbetween0.15to0.50, most of the low-cloud albedo is beatween0.3to0.7and65%of low-cloud is more than0.5, most of the albedo of sea-surface is less than0.15and most of the middle-cloud/high-cloud is bigger than0.6; most of the albedodifference of the sea-surface and middle-cloud/high-cloud between channel19and channel18from MODIS is bigger than0.015, and most of the difference ofsea-surface is less than0.015; most of the albedo of the sea-surface and sea-fogchannel26from MODIS is less than0.02, and most the albedo ofmiddle-cloud/high-cloud is bigger than0.02.2. for nighttime, most of bright temperature difference of the sea-surface andmiddle-cloud/high-cloud between channel31and channel20(BT31-BT20) fromMODIS is bigger than1K,80%of the difference of sea-surface and70%of thedifference of low-cloud are smaller than1K; most of the bright temperaturedifference of the middle-cloud/high-cloud between channel31and channel28(BT31-BT28) from MODIS is about2K, and most of the difference of sea-fog isbetween17K to27K.The thresholds used to detect the sea-fog can be determinded by the spectralproperities. Compared with the sea-fog regions detected by using the the previousthresholds, the sea-fog regions detected by using the thresholds got from newstatistics are more comprehensive. The algorithm used to calculate the real thickness of fog by optical thickness isverfied by the CALIOP data.The real thickness is calcauled and is used to calculatethe visibility. In the mean time, applicability of MODIS-based sea-fog ditection isanalyzed by using the CALIOP cloud data and it proves that the MODIS can be usedto detect sea-fog on the Yellow-Sea.This thesis shows that the CALIOP can be used to inspect the accuracy ofMODIS-based sea-fog detection method and improve the method.