【摘要】：合成孔徑雷達(dá)(Synthetic Aperture Radar,SAR)是二戰(zhàn)之后新興的一種全天時全天候的天基雷達(dá),主要應(yīng)用于機(jī)載和星載平臺,星載SAR系統(tǒng)主要由若干個衛(wèi)星雷達(dá)按照一定的空間構(gòu)型組成。與常規(guī)SAR系統(tǒng)相比,星載SAR系統(tǒng)具有空間自由度高、系統(tǒng)復(fù)雜度低、工作模式多樣等優(yōu)勢,應(yīng)用領(lǐng)域十分廣泛。實際的星載SAR場景中雜波表現(xiàn)出距離非平穩(wěn)特性,同時在一個相干積累間隔(Coherent Processing Intervals,CPI)內(nèi)目標(biāo)與SAR系統(tǒng)的距離走動超過了一個距離單元(稱之為長CPI模式)。據(jù)此本課題在建立立體陣SAR目標(biāo)和雜波回波信號模型后,研究運動目標(biāo)和雜波的頻譜特性,在此基礎(chǔ)上研究距離非平穩(wěn)雜波抑制算法和長CPI模式下的雜波抑制技術(shù)。本文主要的研究內(nèi)容和成果如下:(1)研究空間立體陣星載SAR系統(tǒng)下目標(biāo)和雜波的回波信號模型、動目標(biāo)模型,討論目標(biāo)運動對于距離徙動、多普勒頻率以及多普勒調(diào)頻率的影響。分析雜波的產(chǎn)生機(jī)理以及回波信號中的雜波來源,討論不同分布的雜波的概率密度。得出了K分布雜波能夠有效地模擬其它多種雜波的結(jié)論,利用球不變隨機(jī)過程法生成K分布雜波用以抑制算法。(2)在距離非平穩(wěn)雜波背景下研究空間立體陣星載SAR系統(tǒng)的空時自適應(yīng)處理(Space Time Adaptive Processing,STAP)算法以及降維方法。首先分析雜波的空時特性,研究常規(guī)STAP算法對于非平穩(wěn)雜波進(jìn)行抑制的有效性。研究距離向非平穩(wěn)雜波的頻譜特性以及對回波信號的影響,發(fā)現(xiàn)非平穩(wěn)雜波的頻譜特性與俯仰向信息有關(guān)。根據(jù)立體陣系統(tǒng)雷達(dá)構(gòu)型的特點,將常規(guī)STAP算法擴(kuò)展到空(方位向)—時—空(俯仰向)三維STAP算法。利用回波信號中增加的目標(biāo)和雜波的俯仰維度信息,實現(xiàn)對非平穩(wěn)雜波的抑制,仿真結(jié)果表明三維STAP算法對距離非平穩(wěn)雜波有較好的抑制效果。研究局域聯(lián)合處理(Joint Domain Localized-JDL)方法和先時后空自適應(yīng)(3DT-STAP)方法在降低算法運算量和保證輸出信噪比(Signal Interference Noise Ratio,SINR)的性能。(3)研究長CPI和短CPI模式SAR系統(tǒng)信號頻譜之間存在的差異,研究雜波的頻譜特性后發(fā)現(xiàn)常規(guī)STAP技術(shù)已經(jīng)不能繼續(xù)適用,將全時空信號投影在頻率—多普勒域子空間內(nèi),根據(jù)子空間內(nèi)雜波的獨立性對全空時信號進(jìn)行降維處理,在子空間內(nèi)部進(jìn)行局部STAP處理,將全部子空間的處理結(jié)果利用靜止目標(biāo)斜視成像算法進(jìn)行相干積累,最后利用仿真實驗驗證局部STAP處理和相干積累結(jié)果的有效性,分析CPI的大小以及衛(wèi)星基線的長短對于STAP處理結(jié)果的影響。
[Abstract]:Synthetic Aperture Radar (Synthetic Aperture Radar,SAR) is a new type of space-based radar which is developed after World War II. It is mainly used in airborne and spaceborne platforms. Spaceborne SAR system is mainly composed of several satellite radars in a certain space configuration. Compared with conventional SAR system, spaceborne SAR system has many advantages, such as high degree of freedom in space, low system complexity, various working modes, and so on. In the actual spaceborne SAR scene, the clutter shows a non-stationary range, and the range walk between the target and the SAR system in a coherent accumulation interval (Coherent Processing Intervals,CPI) exceeds a range unit (known as the long CPI mode). Based on this, the spectral characteristics of moving targets and clutter are studied after the establishment of stereo array SAR target and clutter echo signal model, and the range nonstationary clutter suppression algorithm and the clutter suppression technique under long CPI mode are studied. The main contents and achievements of this paper are as follows: (1) the echo signal model and moving target model of target and clutter in space-borne spaceborne SAR system are studied, and the effects of target motion on range migration, Doppler frequency and Doppler modulation frequency are discussed. The generation mechanism of clutter and the source of clutter in echo signal are analyzed, and the probability density of clutter with different distribution is discussed. It is concluded that K-distributed clutter can effectively simulate other kinds of clutter. The spherical invariant random process method is used to generate K-distributed clutter to suppress the algorithm. (2) Space-time adaptive processing (Space Time Adaptive Processing,STAP) algorithm and dimensionality reduction method for space-time adaptive processing of spaceborne SAR systems with space stereoscopic array are studied in the background of non-stationary clutter. Firstly, the space-time characteristic of clutter is analyzed, and the effectiveness of conventional STAP algorithm to suppress non-stationary clutter is studied. The spectral characteristics of the range nonstationary clutter and its influence on the echo signal are studied. It is found that the spectrum characteristics of the non-stationary clutter are related to the pitching information. According to the characteristics of radar configuration of stereo array system, the conventional STAP algorithm is extended to three dimensional (azimuth)-time-air (pitch) STAP algorithm. The suppression of non-stationary clutter is realized by using the additional target information and pitch dimension information of clutter in echo signal. The simulation results show that 3D STAP algorithm can suppress the non-stationary clutter in distance. The performance of the local joint processing (Joint Domain Localized-JDL) method and the first time posterior space adaptive (3DT-STAP) method in reducing the computational complexity and ensuring the output signal-to-noise ratio (Signal Interference Noise Ratio,SINR) is studied. (3) the differences between the signal spectrum of the SAR system with long CPI and short CPI mode are studied. After studying the spectral characteristics of clutter, it is found that the conventional STAP technique is no longer applicable. The whole space-time signal is projected in the frequency-Doppler subspace, and the dimension reduction of the space-time signal is carried out according to the independence of the clutter in the subspace. The local STAP processing is carried out inside the subspace, and the processing results of all the subspaces are integrated by the static target squint imaging algorithm. Finally, the effectiveness of the local STAP processing and the coherent integration result is verified by the simulation experiment. The influence of the size of CPI and the length of satellite baseline on the processing results of STAP is analyzed.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TN957.51

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