Research On Cloud Optical Transmission Characteristics Based On Satellite Data

The cloud coverage accounts for approximately 60% of the Earth's surface and accounts for approximately two-thirds of the average Earth's albedo.The cloud can regulate the radiation budget of the Earth's gas system.On the one hand,the cloud absorbs and scatters the shortwave radiation of the sun,and the albedo effect can reduce the temperature of the ground gas system;on the other hand,the cloud can also absorb and reflect the long-wave radiation of the atmosphere below the surface and the cloud,and the greenhouse effect can warm the ground gas system.Therefore,studying clouds has great significance for atmospheric radiation,climate,human activities and scientific research.This thesis aims to study the cloud physical characteristics and the influence of the cloud on the radiated dispersion characteristics of the target by using the satellite data collection radiative transmission mode.The satellites used are mainly Fengyun satellite and MODIS sensor data.The MODIS sensor data not only provides experimental data,but also provides a reference for the experimental results of Fengyun satellite data.The paper mainly analyzes cloud coverage,cloud classification,optical thickness and cloud radiation.Firstly,cloud coverage and cloud classification adopt multi-spectral threshold detection method.When the cloud detection is introduced,the “confidence model” is introduced to greatly improve the detection accuracy,and the threshold of multiple channels is used to detect cloud pixels;The visible light channel is used to invert the optical thickness of the cloud,and the SBDART radiation transmission mode is used to establish a radiation lookup table under the same observation geometry conditions,underlying surface type,atmospheric environment,etc.Finally,the radiation characteristics of the cloud are studied,mainly based on the cloud transmittance and emissivity in the infrared band.The cloud transmittance needs to be corrected and calibrated to obtain the parameters of the thickness of the cloud and the water content of the cloud.The empirical formula is used to calculate the cloud transmission rate.In order to ensure the reliability of the data and the credibility of the test results,the MODTRAN simulation results are used to compare the final experimental results.The emissivity is calculated based on the conservation of energy.The data calculated in the previous calculation and the reflectivity in the MODIS instrument are substituted into the optical energy calculation formula,and the calculated results are compared with the acquired emissivity in the MODIS data.The comparison results of the two tend to be consistent.In order to combine the research results into practical applications,after the experimental examples of cloud detection,cloud classification,optical thickness,etc.,this paper analyzes the probability distribution and seasonal variation of cloud coverage,cloud classification and cloud optical thickness in Northwest China.This enables researchers to understand the physical characteristics of clouds in the northwest region more intuitively and deeply,and enrich the research content of Chinese cloud characteristics.The above results show that the cloud coverage in the northwest is about 45%,and the cloud coverage varies with the seasons.Among them,the classification of clouds is mainly high clouds,low clouds and cumulonimbus clouds.The probability of cirrus clouds appearing in high clouds is large,and the probability of occurrence of cirrus clouds varies little with the seasons.The optical thickness of the cloud is mainly distributed between 10 and 25,and the average optical thickness is mainly concentrated at about 22.The optical thickness of the cloud in winter is relatively small,and the thickness of the cloud optics has a certain relationship with the season.