Research On Microwave Radiation Characteristics Of Air-Sea Boundary Layer And Its Application In SSWS Remote Sensing

The sea-air boundary layer is a general term for the ocean and the atmospheric boundary layer above it.It is a bridge for the exchange of matter,momentum and energy between the ocean and the atmosphere.The sea-air boundary layer is a difficult point in tropospheric atmospheric remote sensing due to its severe diurnal and complex morphological changes.Remote sensing of the air-sea boundary layer plays an important role in weather forecast,meteorology,marine economic support and oceanography.Microwave radiometer is an effective remote sensing method for sea surface parameters and atmospheric boundary layer parameters.Based on the mapping relationship between measured brightness temperature and sea surface and atmospheric parameters,sea surface parameters and atmospheric parameters can be obtained by inversion of measured brightness temperature.This paper carried out deeply the sea-air boundary layer radiation characteristics of microwave,microwave radiometer measurement system and remote sensing of sea-air boundary layer,first introduced the atmospheric parameters,the atmospheric refractive index calculation method and its changes with height of the model,this paper introduces the thermal radiation and atmospheric downwelling,the surface upwelling bright temperature model,and put forward the model suitable for low elevation of atmospheric downwelling bright temperature;Secondly,the parameters and calibration method of the low elevation brightness temperature measurement system are given,and two comprehensive experiments of microwave radiation in the sea-air boundary layer and data processing methods are introduced.Thirdly,the brightness temperature characteristics of the air-sea boundary layer are deeply analyzed and discussed.Finally,based on the radiation characteristics of the air-sea boundary layer,sea surface wind speed is studied by remote sensing.The main research contents and achievements of this paper are as follows:1.The standard tropospheric atmospheric model,the structure characteristics of refractive index profile and the statistical probability distribution of refractive index of sea surface are systematically described.ITU-R P.835-5 global annual mean reference atmosphere is introduced.The calculation method of tropospheric refractive index,the surface refractive index and its variation model with height are described in detail.Common refractive index models are introduced,such as linear model,ITU index model,double index model,subsection model and Hopfield model.The atmospheric refraction index and its relation among seven different atmospheric refraction types are given,and the atmospheric duct trap refraction environment is described emphatically.The concept of atmospheric boundary layer and remote sensing method are introduced.The similarity theory and the atmospheric waveguide prediction model based on the similarity theory are given,and the PJ model and NPS model are emphasized.The correlation between atmospheric duct and meteorological parameters is analyzed from two aspects of atmospheric standard model and evaporation duct model.2.The modeling methods of the descending brightness temperature of the atmosphere and the ascending brightness temperature of the sea surface are systematically described,and the modeling method is extended from the 1D radiometric transmission equation at high elevation to the 2D radiometer transmission equation at low elevation.When the elevation angle is low,the brightness temperature of the atmosphere in the main beam of the groundbased microwave radiometer varies greatly at different elevation angles by using 2D(azimuth,elevation)antenna direction diagram to weight the brightness temperature at different elevation angles.A method of geometric optical ray tracing is proposed to correct the microwave radiation path at low elevation,and a brightness temperature model of low elevation microwave radiation is proposed.3.A large aperture X/Ku dual-band horizontal/vertical dual-polarization four-channel microwave radiometer measurement system is developed and its overall functions and indexes as well as the components and indexes of each subsystem are introduced.The rationality of this system for low-elevation atmospheric brightness temperature observation is analyzed in detail.Furthermore,the experimental scheme and data acquisition of 2018 Qingdao Sea area and 2019 Bohe Sea area based on the measurement system are introduced in detail,including equipment calibration method,data preprocessing method and model building method.4.The brightness temperature characteristics of sea-air microwave radiation at low elevation are studied based on field experimental data.The variation characteristics of radiant temperature with elevation Angle,temperature,humidity and wind speed at different elevation angle are studied.The causes of experimental phenomena are analyzed and discussed in terms of physical mechanism.The results show that the theoretical analysis is in good agreement with the measured data.5.A prediction model of sea surface wind speed based on low elevation brightness temperature ratio remote sensing is proposed,and simplified models are obtained in different wind speed intervals.Based on the measured data,the model parameters were fitted,and the remote sensing model of sea surface wind speed in low and high wind speed interval was obtained,and the model accuracy was analyzed.The results show that in the low wind speed range(<4.9 m/s),and the optimal RMSE of sea surface wind speed is 0.9544 m/s.In the high wind speed range(>4.9 m/s),the optimal RMSE of sea surface wind speed is 1.1349 m/s.