عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Clouds, because of their significant effects on energy balance on the ground surface and in the atmosphere, has always been considered by different meteorologists and climatologists. The ability of remote sensing in the assessment of cloud characteristics has been proven by in the study of their changes in different locations and times. One of the important aspects of the study regarding the clouds, is to determine the pressure at their top, which the aim of the current study is to present a fast method for its determine by using MODIS images.
Therefore, by using Radiosonde data in Mehrabad and Kermanshah stations, the atmospheric temperature profile was extracted. Then using a five stages technique, the pixels of the considered image were grouped into 4 different categories including cloudy, possibly cloudy, possibly non- cloud and non- cloudy. Then by using LSE model on channels 31 and 32 of MODIS, the emissivity of cloud in cloudy pixels was determined.
Then by using this temperature and the temperature profile extracted from Radiosonde data, the pressure at the top of the clouds were extracted. To review the accuracy of the obtained results, the results obtained from Fast CTP method with those of standard CTP method were compared . Based on this comparison, it is found that the presented method for the clouds with optical depth of more than 10 is optimal and the results obtained from CTP model, shows a very small difference. But the difference regarding the thin clouds with low optical depth (lower than 10) is considerably great in comparing with the clouds of high optical depth.