| Time-varying sea clutter seriously affects the detection performance,when airborne multichannel radar detecting targets in the background of sea surface.Therefore,the degree of knowledge of the space-time characteristics of sea clutter is closely related to the sea clutter suppression capability.In order to achieve a full study of the space-time characteristics of sea clutter,it is indispensable to obtain a large amount of multi-channel sea clutter data.The study of the space-time characteristics of sea clutter based on measured data,which is important for the assessment of the performance of sea clutter suppression by space-time adaptive processing technique in the background of sea surface.In this thesis,a shore-based multi-channel radar measurement system based on transceiver co-location technique and IDPCA technique is established.Meanwhile,this thesis also proposes the amplitude-phase correction and external calibration processing method of the multi-channel radar sea clutter measurement system,which can simulate the movement of the airborne platform and obtain the sea clutter data with the spatial and temporal coupling characteristics.Based on analyzing the multi-channel sea clutter measurement data,a multi-channel sea clutter model is established,and the variation of the sea clutter space-time two-dimensional characteristics with radar parameters and ocean environment parameters is analyzed.Meanwhile,based on the spatial and temporal two-dimensional characteristics of the multi-channel sea clutter,multi-channel sea clutter suppression methods and their applicability are carried out.The main research contents and the results obtained are as follows:1.To address the problem of shore-based multi-channel radar simulation to achieve airborne platform motion function,based on the airborne multi-channel radar clutter spatial characteristics,by comparing the differences between DPCA and IDPCA technique,the basic conditions and principles of clutter spatial coupling characteristics are analyzed in depth.According to the principle of which based on the transceiver co-location technique and the combination of the IDPCA technique shore-based multi-channel radar,the basic conditions and principles of the clutter appearing spatial coupling characteristics is analyzed deeply.Meanwhile,the airborne platform motion simulation method is verified by comparing the relative frequency shift of the calibration body,which is based on the shore-based multi-channel radar measurement system.For the problem of calibrating the multi-channel radar measurement system,the amplitude-phase correction processing method combining the channel dimension and the pulse dimension is proposed,and based on the amplitude-phase correction test data,the amplitude-phase coefficients are updated between channels,which greatly improves the amplitude-phase consistency between channels.The amplitude-phase consistency between channels is greatly improved by updating the amplitude-phase coefficients between channels based on the amplitude-phase correction test data.At last,a method which synthesizing the system constants of multichannel calibration based on the system constants of single-channel calibration is proposed,the differ between the system constants obtained by the proposed method and that from those obtained by the synthetic mode directly based on the test data calibration is0.37 d B,thus verifying the validity of the multichannel radar calibration method.2.To address the sea clutter modelling problem based on the shore-based multi-channel radar measurement system,the sea clutter signal model of the shore-based multi-channel radar is proposed from the analysis of the sea surface theoretical model and the analysis of the shore-based multi-channel radar measurement system model,based on the sea surface motion velocity and sea surface scattering intensity corresponding to each bearing at each moment.The sea clutter signal model contains the elements: the sea clutter theory model mainly involves the sea surface motion velocity model,which mainly involves the sea surface motion velocity model,the two-scale sea surface backscattering coefficient model,the broken wave model and the amplitude distribution model;the shore-based multi-channel radar measurement system model involves the transceiver distance and transceiver antenna direction map factor corresponding to each moment.Based on the principle that the echo power of multi-channel sea clutter is superimposed by multiple azimuthal sub-patches in the equidistant ring,the simulation methods of multichannel sea clutter data of single CPI with multiple range gates and multiple CPIs with single range gate are proposed respectively.Through the comparative analysis of the spatial characteristics quantities based on the measured data and the simulated data,it can be seen that the multichannel sea clutter data based on the simulation method of multiple CPIs with single range gate is more suitable to the real multichannel sea clutter data.The multi-channel sea clutter data generated by the single-distance gate multiple CPIs simulation method can be seen to be more suitable for the measured data.3.Based on the characteristics of L-band multi-channel sea clutter data,a kind of sea clutter data processing method based on shore-based multi-channel radar is proposed to achieve non-uniformity detection of multichannel radar data and echo power variability compensation.A method for quantifying the eigenvalues of sea clutter and a method for quantifying the spreading of the sea clutter space-time power spectrum using the 3 d B clutter ridge spreading metric is proposed.Based on the measured sea clutter data of five sea conditions in L-band,the effects of sea surface parameters and radar operating parameters on the space-time characteristics of sea clutter are analyzed respectively,among which the sea surface motion speed and sea conditions,and the radar operating parameters are mainly polarization and pulse repetition frequency.At the same time,based on the sea clutter measured data,the influence of sea clutter and CNR on the correlation of sea clutter channels is analyzed,it gets that he higher the sea state,the smaller the correlation of the channels when the same CNR is obtained.Meanwhile,the influence of the change of sea state and CNR on the eigenvalue spectra of sea clutter frequency domain is analyzed,it gets that the higher the sea state,the more the number of eigenvalues of the eigenvalue spectra of the frequency domain corresponds to and the bigger the eigenvalues are when the same CNR is obtained.4.To address the problem of sea clutter space-time adaptive processing suppression,the PRI-staggered post-Doppler method,3DT method and cross spectral method are introduced respectively.Then,a multi-channel sea clutter suppression processing algorithm combining PRI-staggered post-Doppler method and CSM method is proposed.With comparing the sea clutter suppression results of the 1DT,3DT and proposed method respectively under sea state 2 and 5,the proposed algorithm suppression performance is best both under high and low level sea states.To address the applicability of the multi-channel sea clutter space-time characteristics,a method which for modelling the difference in space-time characteristics of sea clutter based on the difference in the number of sub-patch in the range ring for wide and narrow transmit beam width.The effects of the beam width on the eigenvalue spectrum,the space-time power spectrum and the SCNR loss curve are compared and analyzed based on the measured data of three different beam width. |
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