A Study On The Passive Microwave Remote Sensing Of Rain Rate And Wind Vector Under Different Weather Conditions

Polarimetric microwave radiometer is an important component in passive remote sensing,and plays a key role in retrieving some geophysical parameters such as wind field and rain rate information.Recently,there has been an increasing interest in the principle of microwave radiation measuring and fully polarimetric radiation at home.This thesis focuses on remote sensing of rain rate and wind filed information under different weather conditions with the purpose of providing technical support and theoretical guidance for ground-based application system of polarimetric microwave radiometer.The radiative transfer model has a pivotal role in retrieving wind filed and intercalibration between similar microwave radiometers.On the basis of microwave radiometric techniques,this study develops a parameterization equation of atmosphere and ocean for retrieving wind filed.The results show that the atmosphere module is the main error source when calculating brightness temperatures?TBs?,and the deviation will increase with the increasing of frequency.The deviation is relatively small for the ocean module.Measurments can be used to calibrate this deviation in the actual application.Based on radiative transfer computations,the double difference method is used to perform intercalibration between HY2 microwave radiometer measurements and SSMIS TBs.Some differences are found between them,and these radiometric differences are corrected effectively by using a second-degree polynomial equation.According to electromagnetic radiation and transfer theory,sea wind vector,sea surface temperature,vapor,and cloud liquid water are retrieved by using the WindSat measurements.WindSat is the first spaceborne fully-polarimetric microwave radiometer.A chaotic particle swarm approach is used to determine a set of possible wind vector solutions by minimizing the difference between the radiative transfer computations and the WindSat TBs.Based on the ECMWF analysis data,an improved circular median filtering function is used to remove wind direction ambiguity.The root-mean-difference is less than 20oby comparing with the QuikSCAT wind direction measurements.One of the major applications of satellite passive microwave data is the study of marine severe weather systems.The low frequencies,such as 6.9 and 10.7 GHz,can be used to retrieve wind speed under severe weather conditions.For accurate retrievals of wind speeds under rainy conditions,the method of channel combination at different frequencies is used.The core of this algorithm make it possible to reduce the signal coming from rain without reducing wind speed signal too much.Two new parameters W6H and W6V are defined,and a wind speed retrieval algorithm for wind speed above20 m/s in hurricanes has been performed by using the two new parameters.The TBs are obtained from three different radiometers.The results show that the retrieved results have a good agreement with the H*wind analysis wind speed and SFMR measurements.The retrieved wind speeds?hurricane Isabel,super typhoon Nepartak and Vongfong?clearly show the process of hurricane intensification and weakening.The change of typhoon's wind direction is 360oat a tangent to a circle.Symmetric wind directions show a phasic difference of 180o.The variations of TB₃ and TB₄ around the eye are consistent with the change in wind direction for closed 360ocirculation.TB₃and TB₄ are robust in that they are insensitive to the influences of atmospheric emission.Thus,we focus on the wind direction signal of TB₃ and TB₄.An apparent directional dependence are found in TB₃ and TB4.As for WindSat 10-GHz TB₃,it is straightforward to identify 4⁶ K peak-to-peak signals in the 20³0 and 30⁴0 m/s bins.Similarly,it shows 2³ K peak-to-peak signals in WindSat 10-GHz TB₄.The directional characteristic are controlled by the first harmonics.The geophysical model function of wind-direction signal is established from matchup dataset between WindSat polarimetric TBs and H*wind analysis wind directions.Overall,the retrieved wind direction results?hurricane Isabel,Fabian,and Rita?are consistent with those of H*wind analysis system.Due to the influence of strong precipitation and the complex sea state background,some deviation are found in some regions.Satellite passive microwave radiometer TBs give information on emission from raindrops and scattering by frozen particles.These measurements play an important role in retrieving global precipitation.Under the conditions of tropical cyclone,the TB difference between 6.9 and 10.7 GHz channels are mainly controlled by rain,and microwave emission from ocean surface influences it slightly though when wind speed is relatively high.A rain parameter?WRH?is defined by using AMSR2 C-band and X-band channels.The results show a non-linear behavior of WRH as a function of rain rate.The change amplitude of WRH is approximately 28 K as the rain rate changes from 0 to 25mm/h,and approximately 12 K as the rain rate changes from 25 to 60 mm/h.Comparing with the GPROF rain rates,the statistical results show that the retrieved rain rates are approximately unbiased and the overall root-mean-square differences is better than 1.2mm/h.The new model is applicable for estimating rain rate up to 60 mm/h.The case studies?typhoon Goni,Halong,and Iselle?show that the retrieved rain rate clearly show the process of typical cyclones'intensification and weakening.