Detection Of Low-Altitude Wind Shear Aided By Geographic Information

For civil aviation aircraft,airborne weather radar plays an important role as the human eye.When the airborne weather radar is operating in the down-look mode to detect low-altitude wind shear,the radar echo signal also contains higher-intensity ground clutter echoes.When the ground clutter environment is uniform,the space-time adaptive processing(STAP)technology based on the maximum likelihood criterion can achieve effective clutter suppression and low-altitude wind shear detection.However,in a complex environment,the non-uniformity of the ground clutter leads to the mismatch of the estimated clutter covariance matrix,which cannot sufficiently suppress the strong clutter,and thus the detection result of the low-altitude wind shear is inaccurate.With the development of STAP technology and the improvement of radar information interaction performance,the method of improving the overall performance of radar with the electronic information database(such as map data,surface coverage data,digital elevation data,etc.)related to geographic information has attracted more and more attention.This also proves the value of a priori geographic information in STAP.This thesis applies the geographical information-assisted STAP technology to the detection of low-altitude wind shear in a complex non-uniform clutter environment.The modeling of high-fidelity non-uniform clutter is studied,and two kinds of non-uniform clutter suppression and low-altitude wind shear wind speed estimation methods assisted by geographic information are proposed.Firstly,based on the echo data characteristics of airborne weather radar,the thesis models low-altitude wind shear signal and non-uniform clutter.A high-fidelity non-uniform clutter simulation method for airborne weather radar assisted by digital elevation model(DEM)and digital land classification data(DLCD)is proposed,and the clutter characteristic is analyzed.The simulation results show that the proposed method improves the accuracy and authenticity of non-uniform clutter simulation.Secondly,for the wind speed estimation of low-altitude wind shear under partial non-uniform clutter environment,a method of wind speed estimation of low-altitude wind shear assisted by echo power screening and DLCD is proposed.The method combines echo power screening with DLCD.Firstly,the sample is first selected according to the sample power,then the sample similarity is calculated according to the geomorphic classification data in the DLCD,and the sample similarity is again selected from the high power sample.The sample is used as a training sample to estimate the clutter covariance matrix of the distance unit to be tested,so as to ensure that the selected training samples can have the same distribution as the clutter of the distance unit to be tested,and finally,the effective wind speed estimation of low-altitude wind shear is realized by the method of combined space-time main channel adaptive processing.The experimental results show that the proposed method can achieve accurate wind speed estimation of low-altitude wind shear.Finally,for the environment with severe clutter non-uniformity,a method of wind speed estimation of low-altitude wind shear assisted by direct data domain(DDD)and geographic information is proposed.The method first selects the non-uniform distance units based on the priori geographic information,and uses DDD method to estimate the distance coherence matrix of the distance dependence and the non-uniform distance units.Then the maximum likelihood method is used to estimate the clutter covariance matrix of the residual uniform distance units.Finally,the generalized adjacent multiple-beam(GMB)method is used to achieve effective wind speed estimation of low-altitude wind shear.The experimental results show that the proposed method has excellent wind speed estimation performance under non-uniform clutter background.