Low-Altitude Windshear Ambiguity Resolution Based On Millimeter Wave LFMCW Radar

As a disastrous atmospheric phenomenon in the field of aviation meteorology,low-altitude windshear has the characteristics of sudden occurrence,short duration and high risk.Millimeter wave linear frequency modulated continuous wave（LFMCW）radar has the strengths of short wave length,wide frequency band,narrow beam,high detection accuracy,and can be used to detect low-altitude windshear.However,the short wavelength of millimeter wave constrains the measurable unambiguous velocity that can be measured by the system,resulting in low-altitude windshear velocity ambiguity and ground clutter Doppler ambiguity,seriously hinder target detection.Therefore,based on the millimeter wave LFMCW system,this thesis focuses on the low-altitude windshear velocity ambiguity resolution under the background of strong clutter.Firstly,the signal processing principle of millimeter wave LFMCW radar system is described.The transmitted signal adopts the form of multiple frequency pulse group stagger,and the low-altitude windshear and ground clutter echo data under the condition of multiple frequency pulse group stagger are obtained by simulation,which lays the foundation for the following chapters.Secondly,aiming at the problem of low-altitude windshear velocity ambiguity caused by short wavelength in millimeter wave band,a velocity ambiguity resolution method based on improved one-dimensional set algorithm is proposed.Firstly,the robust two-dimension pulse-to-pulse canceller（RTDPC）prefilter is designed by using radar related parameters to pre-filter the radar echo,and then space-time amplitude and phase estimation is used to perform two-dimensional filtering on the pre-filtered data to obtain the low-altitude windshear fuzzy speed estimation.Then one-dimensional set improved algorithm is used to realize speed ambiguity resolution,and the accurate estimation of low-altitude windshear wind speed is obtained.Finally,the average F factor of wind speed is calculated,and the risk judgment is given.This method not only ensures the high precision of ambiguity resolution,but also significantly reduces the amount of computation.Finally,considering that the space-time adaptive processing algorithm needs to solve the clutter covariance matrix and its inverse matrix when calculating the adaptive weights,the algorithm has high computational complexity,a low-altitude windshear ambiguity resolution method based on compressed sensing is proposed.In this method,the non-uniform under sampling characteristics of multiple PRF echo are used to construct the unambiguous sensing matrix in the angle Doppler domain.Then,the related reconstruction algorithm is used to recover several large clutter components,estimate the clutter energy support domain,and the clutter suppression matrix is constructed and the restoration vector is weighted.Then,the minimum₁l norm optimization model is used to suppress the ground clutter and recover the unambiguous Doppler frequency of the signal,so as to realize the effective estimation of the low-altitude windshear wind speed.Finally,the F factor is calculated to determine the danger.This method does not need to calculate the adaptive weights,and thus does not need to solve the clutter covariance matrix,and has higher angle and Doppler resolution.