Sea Fog Retrieval And The Applicability Of Retrieval Basing On MODIS Data

In this paper, through the analysis of spectral characteristics of target ,such as the sea surface without cloud, cloud and so on, detect a new dynamic method to find the sea fog area from the stratus clouds, improving the satellite detection algorithm of day-sea fog method. Using this new method, discuss the sea fog retrieval applicability in Yellow Sea and Bohai sea.Firstly, summarize the spectral characteristics of sea surface targets on different wave bands such as visible light, short infrared, middle infrared, far infrared spectral features, and then successfully use the static threshold method,NDSI (normalized difference snow index),land-sea templates and other templates to distinguish the low clouds / sea fog, high clouds, land and sea without clouds from the surface targets. Using four years of L-band radar sounding data, differences in vertical physical property between sea fog and low cloud are given, and then detect a new dynamic method of making out the sea fog area from the mix area of sea fog and low clouds, finally improve daytime sea fog retrieval algorithm based on MODIS data. Present one sea fog retrieval example on May 1, 2008 Yellow Sea. The retrieval results are well matched up with the observations which contents five air sounding station observations around the Yellow Sea and one ICOADS observation in the Yellow Sea.Retrieving years of the MODIS data with the new sea-fog detection algorithm shows that the high values in frequency of sea fog are well matched the frequency of sea fog frequency based on the ICOADS data lasting from 1796-2009.But,because of low clouds and middle-high clouds influence on the south of Yellow Sea, the high frequency values in day and night can not be found in ICOADS frequency. After analyzing cloud cover in the Yellow Sea and Bohai Sea using CFSR data, the applicability of the sea fog retrieval has researched. Result shows, in the Bohai Sea, from the October to the March at next year cloud frequency always higher than 50%,during this time, it is unfavorable to detect sea fog; if we focus on the Yellow Sea, from the March to June cloud frequency is lower, especially in the May, it is very disadvantageous to detect sea fog; other time in the year, south of N340,there is high cloud frequency near 70%,which is serious influenced the sea fog detection, especially east sea area to the Yangtse River mouth, cloud frequency is even up to 80%, in this area, fog detection is almost impossible.