| Satellite microwave radiometer plays an important role in studying hydrology,agriculture,meteorological and Earth's water and energy circulation.Current satellite passive microwave observations used in inversion the process of geophysical parameters,such as land surface temperature,snow and surface freezing process,etc.,can make up the inadequacy of the ground observation in time and space.The atmosphere influences are often ignored in the inversion of these parameters(only separated the atmosphere in rain and non-rain condition for simply during research).The atmospheric water vapor,cloud liquid water and precipitation in the atmosphere can affect passive microwave signal when through the troposphere.In order to analyze the atmosphere influence for passive microwave signal and quantify the atmospheric effect for improving the geophysics parameters inversion accuracy,this study focus on analysis atmospheric influence for satellite passive microwave and atmospheric correction for retrieving ground brightness temperature at commonly-used passive microwave frequencies.Under non-precipitating conditions,radiosoundings from 119 stations in China,performed twice a day from January 2011 to July 2014,were used in the Salonen-Uppala cloud detection algorithm to distinguish cloud layers from layered atmospheric profiles,and to estimate the cloud liquid water content therein.The resulting atmospheric transmittances at frequencies of the AMSR-E(The Advanced Microwave Scanning Radiometer-Earth Observing System),MWRI/FY-3B(Microwave Radiation Imager/Feng Yun-3B)and SSM/I(Special Sensor Microwave/Imager)over China were estimated using Liebe's MPM and Mie theory.Atmospheric transmittance maps were obtained by interpolating the results from individual sites,driving a climatological database for over China which may be used to correct for atmospheric influence in surface parameter retrievals.The simulated transmittances were validated through a series of on-site field experiments in the North of China.Using the relationship between microwave transmittance and total precipitable water vapor of MODIS(MYD05),we calculated the microwave atmospheric transmittances and atmospheric downward radiation in 5 km resolution over China.Using microwave radiation transfer equation and atmospheric attenuation function,atmospheric correction method of satellite passive microwave was deduced,which was applied to the atmospheric correction of passive microwave snow cover and snow depth retrieval.The main research contents are as follows:1)we simulated and analyzed the atmosphere influenced of typical passive microwave frequencies under clear sky and cloudy condition,by using the standard atmosphere profile data and typical atmosphere profile of stratus and cumulus cloud,combined with the 1DMWRTM(1 Dimensional microwave radiation transfer model).Passive microwave atmospheric attenuation,atmospheric optical thickness,atmospheric transmittance and downward atmospheric radiation and other physical quantities were calculated under clear sky and cloud covered condition.The impact of different atmospheric media for passive microwave on non-rainy conditions was analyzed.Finally,we found the atmospheric water vapor and cloud liquid water are the main factors that can affect passive microwave high frequency signal(>10.65GHz),especially the cloud liquid water effects on satellite passive microwave signal need to calculate.2)121 atmospheric sounding in situ observations in China in recent four years are collected.The sounding data were used to calculate the atmosphere transmittance at typical passive microwave frequencies twice a day in China by combining with cloud detection model,the MPM(Millimeter Propagation Model)and Mie theory.The result can make up the insufficient of less considering the cloud liquid water in the traditional study of the atmospheric correction.Meanwhile,this study is the first time to get a large area of passive microwave atmospheric transmittance and downward atmospheric radiation.3)We compared the downward atmospheric radiation observed by ground-based microwave radiometer with downward atmospheric radiation calculated by microwave transmittance previously estimated under different elevation angles,different frequencies and different field sites.We also compared the result of atmospheric transmittances we estimated with simulated by 55% fractile model in GlobSnow.All of the validation result showed that the atmospheric transmittances we estimated are reliable and can better reflect the atmospheric transmittance changes with seasons than the transmittance result of 55% fractile model.4)There are good function relationship between microwave atmospheric transmittance and total precipitable water vapor(MOD05),which can help to develop the method of estimating 5km resolution microwave atmospheric transmittance.Then using the zero order microwave radiative transfer equation of space-borne and ground-based microwave radiometer and the theory of microwave atmospheric attenuation,we derived the atmospheric correction method of satellite passive microwave bright temperature observation.After using the atmospheric corrected microwave brightness temperature of SSM/I configured frequencies and traditional snow depth gradient algorithm(19HGHz-37HGHz)we calculated the snow depth over northeast China and Xinjiang area,and compared the results with the ground site snow depth observation.We also calculated the SSM/I's brightness temperature difference(TBD)between 19 GHz and 85.5 GHz at V polarization the sensor cases.The brightness temperature difference were compared with IMS snow cover products,and the comparison results showed that the high frequency TBD(19 V-85.5 V)can well reflect the snow spatial distribution over Qinghai-Tibet Plateau region.We determine a TBD threshold when TBD results have highest correlation with IMS snow cover.Comparing with the original high frequency TBD,passive microwave high-frequency TBD after atmospheric correction can show higher accuracy to make sure snow cover area over Qinghai-Tibet Plateau region. |
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