Research On Simulation Of Signal Transmission Model And Indicators Of Microwave Radiometer System

Since the development of passive microwave remote sensing from the traditional total power microwave radiometer,there have been a variety of new types of microwave radiometers,such as spectrometer and full polarization radiometer,which provide an effective technical way to solve the problem of spectrum information acquisition and full polarization information acquisition of passive microwave remote sensing.The model of the total power radiometer is generally characterized by the traditional superheterodyne receiver,and the transmission process of the signal in the radiometer is qualitatively described based on the traditional method.Through the theoretical analysis of the random signal,the influence of the bandwidth and integration time on the measurement accuracy and sensitivity is obtained.However,with the progress of technology and the improvement of radiometer sensitivity and calibration accuracy,the traditional radiometer modeling methods and models can not meet the needs of continuous development in many occasions.Quantitative remote sensing puts forward more precise requirements for the transfer model of radiometer system and for the precise positioning of error items in the system.In this thesis,three basic radiometers,total power radiometer,spectrometer and full polarization radiometer,are studied.The specific system modeling process is respectively carried out for three in orbit or in pre-study satellite radiometers,namely,the microwave humidity and temperature sounder(MWHTS)of FENGYUN-3 meteorological satellite,the terahertz atmospheric limb sounder(TALIS)and the full polarization Microwave Imager(PMI)to be carried on the water cycle satellite.First of all,by studying and improving some existing radiometer simulation algorithms,a new simulation model which can analyze total power microwave radiometer quantitatively is proposed,including thermal radiation noise model,radiometer front-end model and back-end model.Then the algorithm is applied to MWHTS instrument modeling,and the simulation is compared with the actual dynamic range,sensitivity and linearity to verify the simulation model.Secondly,the simulation analysis of the performance indicators of the total power radiometer is carried out based on this,and a sensitivity estimation algorithm based on the simulation model is proposed.The results show that the maximum error of 15 channels of MWHTS obtained by using this sensitivity estimation algorithm is 16%.At last,aiming at the large irregularity of MWHTS,this thesis evaluates the measurement error of MWHTS SRF to brightness temperature based on the simulation model.Secondly,through the improvement of the thermal radiation noise model and the backend model of the total power radiometer,a simulation algorithm that can quantitatively simulate the spectral radiometer is proposed for the first time,and the algorithm is applied to the instrument modeling of TALIS.The improved thermal noise model could simulate the bright temperature spectrum of the target.The FFT algorithm is used to calculate the target power spectrum.In order to verify the instrument design of TALIS,firstly,the calibration method of TALIS is simulated in this thesis.Secondly,the error analysis and Simulation of the sideband imbalance of DSB are carried out based on the spectral radiometer model.The results show that the maximum brightness temperature error is 0.6 K when the sideband imbalance is less than 0.5%.Thirdly,the model is used to simulate and evaluate the spectral resolution selection of TALIS.The results show that when the spectrum resolution is 2 MHz,the sensitivity and spectrum resolution requirements of TALIS can be met simultaneously.Finally,based on the established model,the quantization errors of different quantization bits of spectrometer are analyzed.The simulation results show that the sensitivity of TALIS is 1.25 K when 8 bit quantization is used,which meets the design requirements.Finally,the simulation model of the full polarization radiometer system is studied.Firstly,by improving the thermal noise signal model of the total power radiometer,the full polarization thermal noise model with phase information is established;based on the theoretical formula of the full polarization calibration source,the thermal noise model of the full polarization calibration source is established.Secondly,the function of IQ orthogonal demodulation is added to the RF front-end model to output IQ signal;the digital correlation module uses the correlation operation of digital correlator and accumulates to achieve the integration function.Thirdly,the simulation model is applied to the system modeling of PMI,and the sensitivity,linearity and calibration residual of the simulation results are analyzed,and measured data are used to verify the correcteness of the simulation model.Finally,the channel gain imbalance,polarization angle error and quantization error are analyzed by using the established model of full polarization radiometer.