基于時(shí)頻分析技術(shù)的機(jī)動(dòng)目標(biāo)ISAR成像方法研究.pdf

1、雷達(dá)成像具有遠(yuǎn)距離、全天時(shí)和全天候的特點(diǎn)，對軍用和民用都有重大實(shí)用價(jià)值。由于雷達(dá)的工作及成像方式的不同，成像雷達(dá)可分為逆合成孔徑雷達(dá)(ISAR)和合成孔徑雷達(dá)(SAR)。在機(jī)動(dòng)目標(biāo)的ISAR成像中，經(jīng)過運(yùn)動(dòng)補(bǔ)償后的回波數(shù)據(jù)可用多分量多項(xiàng)式相位信號(hào)模型來描述，這是一類典型的非平穩(wěn)信號(hào)。實(shí)際對目標(biāo)進(jìn)行成像處理時(shí)可根據(jù)目標(biāo)的運(yùn)動(dòng)特點(diǎn)對這一模型進(jìn)行合理的近似，而成像質(zhì)量的高低在很大程度上取決于信號(hào)處理方法的優(yōu)劣，即可采用信號(hào)處理的方法來提高機(jī)動(dòng)

2、目標(biāo) ISAR成像質(zhì)量。本文基于時(shí)頻分析原理，從參數(shù)估計(jì)與時(shí)頻表示兩個(gè)方面將目標(biāo)回波信號(hào)分為四種情況進(jìn)行研究，分別是：常幅線性調(diào)頻信號(hào)、常幅多項(xiàng)式相位信號(hào)、變幅多項(xiàng)式相位信號(hào)和基于時(shí)頻分布的方法直接得到信號(hào)的時(shí)頻結(jié)構(gòu)，分別提出新的信號(hào)處理方法以提高機(jī)動(dòng)目標(biāo)ISAR成像質(zhì)量。本文主要工作概述如下：
　　1.以飛機(jī)目標(biāo)的外場實(shí)測數(shù)據(jù)為例，研究了一階近似條件下目標(biāo)做機(jī)動(dòng)飛行時(shí) ISAR成像的距離——瞬時(shí)多普勒法原理，其本質(zhì)為多分量線性調(diào)

3、頻信號(hào)的參數(shù)估計(jì)問題。進(jìn)而，研究兩種估計(jì)線性調(diào)頻信號(hào)參數(shù)的超分辨方法在 ISAR成像中的應(yīng)用，在獲得同樣的橫向分辨率條件下，減小了成像所需的觀測角度。最后對目標(biāo)機(jī)動(dòng)運(yùn)動(dòng)情況下的回波信號(hào)特點(diǎn)做出總結(jié)性歸納，并從信號(hào)處理的角度對其進(jìn)行理論分析，進(jìn)而達(dá)到統(tǒng)領(lǐng)全文的目的。
　　2.針對常幅線性調(diào)頻信號(hào)，提出了一種新的線性調(diào)頻信號(hào)參數(shù)估計(jì)方法——三次相位函數(shù)法。新方法通過一維搜索可以得到調(diào)頻斜率的估計(jì)，進(jìn)而通過解調(diào)頻技術(shù)和快速傅里葉變換獲得

4、信號(hào)初始頻率和幅度的估計(jì)，具有較小的計(jì)算量?；谝浑A擾動(dòng)分析原理詳細(xì)推導(dǎo)了該方法的漸進(jìn)統(tǒng)計(jì)特性，理論與仿真結(jié)果均表明該方法具有很高的參數(shù)估計(jì)精度。將該方法應(yīng)用于機(jī)動(dòng)飛行目標(biāo)的ISAR成像中，可提高成像質(zhì)量。
　　3.針對常幅多項(xiàng)式相位信號(hào)，首先提出基于改進(jìn)形式 Wigner-Ville分布(WVD)的三、四次多項(xiàng)式相位信號(hào)參數(shù)估計(jì)方法，解決了 ISAR成像中的轉(zhuǎn)角估計(jì)問題。對于任意階次的多項(xiàng)式相位信號(hào)，本文研究了一個(gè)重要概念——瞬

5、時(shí)頻率變化率，提出兩種估計(jì)瞬時(shí)頻率變化率的新方法，并將其應(yīng)用于多項(xiàng)式相位信號(hào)的參數(shù)估計(jì)中，在保持較高參數(shù)估計(jì)精度的同時(shí)具有較小的計(jì)算量。
　　4.針對變幅多項(xiàng)式相位信號(hào)，提出采用信號(hào)分解的方法對其進(jìn)行分析與處理。信號(hào)分解是信號(hào)處理領(lǐng)域的重要研究內(nèi)容，通過將信號(hào)分解成一系列基函數(shù)的線性組合，可以反映信號(hào)的內(nèi)部結(jié)構(gòu)特征。本文研究了目前比較常用的信號(hào)的自適應(yīng) Chirplet分解，首先提出一種優(yōu)化分解算法，即采用RELAX技術(shù)在估計(jì)當(dāng)前

6、分量的參數(shù)時(shí)，固定其余分量的參數(shù)，逐個(gè)依次調(diào)整，以達(dá)到內(nèi)部收斂，該方法可明顯提高信號(hào)的參數(shù)估計(jì)精度，但計(jì)算量較大。本文提出一種自適應(yīng) Chirplet分解的快速算法，該算法利用計(jì)算信號(hào)的三次相位函數(shù)，得到其能量分布集中于信號(hào)的調(diào)頻率曲線上的結(jié)論，此時(shí)通過譜峰檢測可同時(shí)獲得 Chirplet調(diào)頻率、時(shí)間中心和幅度的估計(jì)，進(jìn)而通過解線性調(diào)頻技術(shù)獲得其初始頻率和時(shí)間寬度的估計(jì)。研究了自適應(yīng) Chirplet分解在如下兩個(gè)方面的應(yīng)用：機(jī)動(dòng)飛行目

7、標(biāo)的ISAR成像和非剛體目標(biāo)的ISAR成像。
　　針對自適應(yīng) Chirplet分解的不足，提出了修正的自適應(yīng) Chirplet分解法，將 Chirplet基函數(shù)推廣到三次相位信號(hào)的形式，可以很好地逼近信號(hào)中的非線性時(shí)變結(jié)構(gòu)成分，給出了相應(yīng)的實(shí)用算法與快速算法。最后研究了基于修正自適應(yīng)Chirplet分解的機(jī)動(dòng)目標(biāo)ISAR成像方法。
　　5.研究信號(hào)的時(shí)頻分布。對于多分量多項(xiàng)式相位信號(hào)，提出三種時(shí)頻分布設(shè)計(jì)新方案，抑制了交叉項(xiàng)

8、的影響，同時(shí)保持較高的時(shí)頻聚集性；提出傳統(tǒng)多項(xiàng)式 Wigner-Ville分布和四階復(fù)時(shí)間延遲型多項(xiàng)式 Wigner-Ville分布的頻域卷積實(shí)現(xiàn)方法，使其適用于分析多分量信號(hào)。最后，研究了基于新型時(shí)頻分布的機(jī)動(dòng)目標(biāo)ISAR成像方法。
　　6.研究外場實(shí)測數(shù)據(jù)的艦船目標(biāo) ISAR成像。提出采用(修正)自適應(yīng)Chirplet分解法或時(shí)頻分布法得到目標(biāo)的瞬態(tài)像，同時(shí)針對多徑效應(yīng)問題，提出在距離——瞬時(shí)多普勒域?qū)δ繕?biāo)初像進(jìn)行分離，進(jìn)而進(jìn)

9、行二次成像的方法，可以很好地解決多徑效應(yīng)情況下高機(jī)動(dòng)艦船目標(biāo)的瞬時(shí)成像問題。對于尺寸較大的目標(biāo)，距離走動(dòng)比較明顯，提出采用 Keystone變換的方法來校正距離走動(dòng)，然后再進(jìn)行方位向壓縮來獲得目標(biāo)ISAR像的方法。
　　Radar imaging has the characteristic of all-weather, day/night and long range, and has great value in civil

10、ian and military applications. Due to the dissimilarity of the Radar’s working mechanism and imaging mode, imging Radar can be divided into two categories-inverse synthetic aperture Radar(ISAR) and synthetic aperture Rad

11、ar(SAR). In ISAR imaging, the echo after motion compensation can be characterized as the model of multi-component polynomial phase signal(PPS), and this is a typical kind of nonstationary signals. When implement the ISAR

12、 image of a target, this model can be approximated logically according to the movement character of the target, and the quality of the Radar images lies on the signal processing technique. That is to say, the quality of

13、the Radar images can be improved greatly by the signal processing methods. This paper divides the echo of the target into four categories from the aspects of parameter estimation and time frequency distribution, they are

14、 the constant amplitude linear frequency modulated(LFM) signal model, constant amplitude polynomial phase signal(PPS) model, time varying amplitude PPS model and directly obtaining the time frequency structure of the sig

15、nal based on the time frequency methods. New algorithms are presented in signal processing corresponding to the four models above in order to improve the quality of the Radar images. The following is the summarization of

16、 the main work:
　　1. The principle of the Range-Instantaneous-Doppler(RID) algorithm for ISAR imaging of maneuvering targets under the condition of one order approximation based on the real data of plane is studied. T

17、he essence of RID is the parameters estimation of multi-component LFM signals. Two kinds of super-resolution techniques for estimate the parameters of LFM signals are studies and are used in the ISAR imaging of maneuveri

18、ng targets, the observation angle for ISAR imaging is decreased whereas the cross resolution is invariant. Finally, the characteristics of the echo for the target which have a maneuvering flight are summarized and analyz

19、ed in the signal processing point of view with the aim of commanding the whole paper.
　　2. The model of constant amplitude LFM signal is considered, and a new algorithm for estimate the parameters of LFM signal based

20、on the cubic phase function(CPF) are presented. The chirp rate can be estimated by a one-dimensional maximization of the CPF, and the initial frequency and amplitude can be obtained by the dechirp technique combining wit

21、h the fast Fourier transform. This method has a low computation complexity, and the asymptotic statistical performance is analyzed by the first order perturbation analysis of maxima of random functions. The simulated and

22、 theoretical results demonstrate the high precision of this algorithm. This new method is used in the ISAR imaging of maneuvering targets and improves the images quality greatly.
　　3. The constant amplitude PPS model

23、is considered, and a new algorithm for estimate the parameters of a cubic or quartic phase PPS based on the modified version of the WVD is proposed, this algorithm is used for the estimate of the rotation angle in ISAR i

24、maging. For an arbitrary order PPS, a new concept-Instantaneous Frequency Rate(IFR) is studied and two new methods for estimate the IFR are presented, this notion is used for the parameters estimation of a PPS with high

25、precision and low computation burden.
　　4. The time varying amplitude PPS model is considered, and the signal decomposition technique is adopted to deal with it. Signal decomposition is a main topic in the signal proc

26、essing domain, by decomposing the signal into a linear combination of a series of atoms, the inner structure of the signal can be revealed. The commonly used adaptive Chirplet decomposition is studied in this chapter, an

27、d an optimum algorithm based on the RELAX technique is presented. This algorithm fixes up the parameters of the rest components while estimating the parameters of the current component, and adjusts the estimated paramete

28、rs one by one until getting the inner convergence. This method can improve the parameters estimation precision but with heavy computation burden. Then a fast algorithm for the adaptive Chirplet decomposition based on the