同軌雙基SAR成像算法研究
發(fā)布時間：2018-09-11 12:12
【摘要】：與傳統(tǒng)的單基合成孔徑雷達不同，雙基地合成孔徑雷達(Bistatic SyntheticAperture Radar, BiSAR)的接收機和發(fā)射機放置在不同的運動平臺上，發(fā)射機和接收機可以有不同的空間位置和速度。因此雙基地SAR在軍事應用，資源調(diào)查和地殼形變監(jiān)測等方面具有特殊的優(yōu)勢。在諸多的雙基SAR構(gòu)型中，同軌雙基SAR的發(fā)射機和接收機以相同的速度沿著相同的航跡勻速直線飛行，這種體制的雙基地SAR編隊構(gòu)形相對簡單，工程上較容易實現(xiàn)，在地面運動目標檢測等方面有著廣闊的應用前景�；诖�，本文對同軌構(gòu)型雙基SAR目標二維頻譜精度和同軌構(gòu)型不同模式下的成像算法進行了一些研究，主要工作概括如下： 1.理論上LBF(Loffeld’s bistatic formula, LBF)雙基SAR目標頻譜適用于任意的雙基構(gòu)型，但是在具體的雙基構(gòu)型條件下其譜精度因不同參數(shù)配置的影響而有所不同。針對同軌雙基地SAR構(gòu)型，本文通過數(shù)學方法將其與一種嚴格解析的雙基目標二維頻譜進行對比分析，詳細推導出了影響LBF雙基譜精度的兩個約束條件。即半雙基角的余弦值大小以及半基線長度與目標到航線的最近距離的比值是否等于半雙基角的正切值。當半雙基角的余弦值等于1，半基線長度與目標到航線的最近距離的比值等于半雙基角的正切值這兩個條件同時得到滿足時，LBF譜是完全嚴格解析的。在這兩個影響譜精度的約束條件中，LBF雙基譜的譜精度對半雙基角的余弦值的大小變化更為敏感，而并不直接受到基線長度和斜視角大小的影響，通過仿真實驗詳細分析討論了各種因素對于LBF譜精度的影響。 2.提出一種同軌構(gòu)型下基于嚴格解析雙基SAR目標二維頻譜的線頻調(diào)變標(Chirp Scaling, CS)成像算法，解決條帶模式下雙基地SAR包絡徙動的空變問題。不同于波數(shù)域的成像算法，整個成像過程不需要進行插值運算，在頻域聚焦實現(xiàn)快速成像。高精度的雙基頻譜使得所提算法對基線的長短不再敏感，可以進行大雙基角，，長基線情形下的同軌雙基SAR數(shù)據(jù)處理。仿真實驗和對比實驗驗證了所提算法的有效性和優(yōu)越性。 3.針對大斜視情形下同軌雙基SAR目標的距離徙動和二次距離壓縮(SecondRange Compression, SRC)的空變性問題，基于嚴格解析的雙基SAR目標二維頻譜，提出了一種適用于同軌構(gòu)型雙基SAR的非線性CS(Nonlinear Chirp ScalingAlgorithm, NCSA)成像算法，不同于適用于小斜視角條件的CS成像算法，非線性CS算法不僅考慮了調(diào)頻率隨多普勒頻率的變化，而且也考慮了其隨距離的線性變化，更好地實現(xiàn)了同軌雙基SAR中SRC的精確補償，取得了滿意的聚焦效果。仿真實驗驗證了所提算法的有效性。 4.對于聚束模式下的同軌雙基SAR構(gòu)型，基于同軌構(gòu)型下嚴格解析的半雙基角和譜分析方法，提出了一種適用于同軌構(gòu)型下聚束式雙基SAR的頻率變標(Frequency Scaling, FS)成像算法。首先，類比單基情形，推導出了雙基地情形下的deramp函數(shù)，實現(xiàn)方位向的粗聚焦，有效地消除系統(tǒng)方位向的頻譜混疊問題。然后基于同軌構(gòu)型下嚴格解析的雙基SAR目標二維頻譜，通過一種適用于聚束式雙基地SAR的FS成像算法校正目標的距離徙動，取得理想的成像效果。FS算法通過相位相乘代替插值操作實現(xiàn)目標的距離徙動校正，可以實現(xiàn)快速成像。精確的雙基頻譜使得所提算法可以進行長基線情形下的數(shù)據(jù)處理。仿真實驗驗證了算法的有效性。此外，針對大斜視情形下SRC的空變問題，提出一種基于嚴格解析雙基頻譜的改進頻率變標成像算法，通過非線性變標操作消除由大斜視導致的隨距離變化的二次距離壓縮項。仿真實驗表明，與常規(guī)FS算法相比，改進算法在大斜視情形下可實現(xiàn)目標良好的成像，點目標沖激響應的主副瓣可清晰分辨。
[Abstract]:Different from the traditional monostatic SAR, the receiver and transmitter of Bistatic Synthetic Aperture Radar (BiSAR) are placed on different moving platforms, and the transmitter and receiver can have different spatial positions and velocities. In many bistatic SAR configurations, the transmitter and receiver of the same-orbit bistatic SAR fly along the same track at the same speed in a uniform straight line. The bistatic SAR formation configuration of this system is relatively simple, easy to implement in engineering, and has a broad application prospect in the detection of ground moving targets. Based on this, the two-dimensional spectral accuracy of bistatic SAR targets with homoorbital configuration and the imaging algorithm under different modes of homoorbital configuration are studied in this paper.
1. Theoretically, the target spectrum of LBF (Loffeld's bistatic formula) bistatic SAR is suitable for any bistatic configuration, but its spectral accuracy varies with different parameter configurations under specific bistatic configuration. For the same-orbit bistatic SAR configuration, this paper uses mathematical method to analyze it with a rigorous bistatic target 2. Two constraints affecting the accuracy of LBF bispectrum are deduced by comparing and analyzing the two-dimensional spectrum, that is, whether the cosine value of the half-bispectrum angle and the ratio of the half-baseline length to the nearest distance from the target to the route are equal to the tangent value of the half-bispectrum angle. The LBF spectra are completely strictly analytic when the ratio of the near distance to the tangent of the half-bistatic angle is satisfied simultaneously. Among the two constraints affecting the spectral accuracy, the spectral accuracy of the LBF bistatic spectrum is more sensitive to the variation of the cosine of the half-bistatic angle, and is not directly affected by the baseline length and the angle of inclination. The influence of various factors on the accuracy of LBF spectrum is discussed in detail through simulation experiments.
2. A chirp scaling (CS) imaging algorithm based on rigorous analysis of two-dimensional spectrum of bistatic SAR targets in the same orbit configuration is proposed to solve the problem of envelope migration of bistatic SAR in strip mode. High-precision bistatic spectrum makes the proposed algorithm insensitive to baseline length and can process homo-orbital bistatic SAR data with large bistatic angle and long baseline. Simulation and contrast experiments show the effectiveness and superiority of the proposed algorithm.
3. Aiming at the range migration and the spatial variability of the second Range Compression (SRC) of the bistatic SAR target in the case of large squint, a nonlinear CS (Nonlinear Chirp Scaling Algorithm, NCSA) imaging algorithm for the bistatic SAR target with the same orbit configuration is proposed based on the strict analysis of the two-dimensional spectrum of the bistatic SAR target. For CS imaging algorithm with small squint angle, the nonlinear CS algorithm not only considers the change of modulation frequency with Doppler frequency, but also considers the linear change of modulation frequency with range. It achieves the accurate compensation of SRC in homo-orbital bistatic SAR, and achieves satisfactory focusing effect.
4. For homo-orbital bistatic SAR configurations in spotlight mode, a new frequency scaling (FS) imaging algorithm for homo-orbital bistatic SAR is proposed based on the rigorous analytical method of semi-bistatic angle and spectrum. Firstly, the deramp function for bi-orbital bistatic SAR is derived by analogizing the single-orbital case. The coarse focusing of azimuth can effectively eliminate the aliasing problem in azimuth direction of the system. Then, based on the two-dimensional spectrum of bistatic SAR target, a FS imaging algorithm suitable for spotlight bistatic SAR is proposed to correct the range migration of the target. FS algorithm uses phase multiplication instead of interpolation. The precise bistatic spectrum enables the proposed algorithm to process data in the case of long baseline. Simulation results show the effectiveness of the proposed algorithm. In addition, an improved frequency based on strictly analytic bistatic spectrum is proposed for the space-variant problem of SRC in the case of large squint. Rate-varying scaling algorithm eliminates the range-varying quadratic range compression term caused by large squint by nonlinear scaling operation. Simulation results show that the improved algorithm can achieve good target imaging and the main and side lobes of point target impulse response can be clearly distinguished compared with the conventional FS algorithm.
【學位授予單位】：西安電子科技大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：TN957.52
[Abstract]:Different from the traditional monostatic SAR, the receiver and transmitter of Bistatic Synthetic Aperture Radar (BiSAR) are placed on different moving platforms, and the transmitter and receiver can have different spatial positions and velocities. In many bistatic SAR configurations, the transmitter and receiver of the same-orbit bistatic SAR fly along the same track at the same speed in a uniform straight line. The bistatic SAR formation configuration of this system is relatively simple, easy to implement in engineering, and has a broad application prospect in the detection of ground moving targets. Based on this, the two-dimensional spectral accuracy of bistatic SAR targets with homoorbital configuration and the imaging algorithm under different modes of homoorbital configuration are studied in this paper.
1. Theoretically, the target spectrum of LBF (Loffeld's bistatic formula) bistatic SAR is suitable for any bistatic configuration, but its spectral accuracy varies with different parameter configurations under specific bistatic configuration. For the same-orbit bistatic SAR configuration, this paper uses mathematical method to analyze it with a rigorous bistatic target 2. Two constraints affecting the accuracy of LBF bispectrum are deduced by comparing and analyzing the two-dimensional spectrum, that is, whether the cosine value of the half-bispectrum angle and the ratio of the half-baseline length to the nearest distance from the target to the route are equal to the tangent value of the half-bispectrum angle. The LBF spectra are completely strictly analytic when the ratio of the near distance to the tangent of the half-bistatic angle is satisfied simultaneously. Among the two constraints affecting the spectral accuracy, the spectral accuracy of the LBF bistatic spectrum is more sensitive to the variation of the cosine of the half-bistatic angle, and is not directly affected by the baseline length and the angle of inclination. The influence of various factors on the accuracy of LBF spectrum is discussed in detail through simulation experiments.
2. A chirp scaling (CS) imaging algorithm based on rigorous analysis of two-dimensional spectrum of bistatic SAR targets in the same orbit configuration is proposed to solve the problem of envelope migration of bistatic SAR in strip mode. High-precision bistatic spectrum makes the proposed algorithm insensitive to baseline length and can process homo-orbital bistatic SAR data with large bistatic angle and long baseline. Simulation and contrast experiments show the effectiveness and superiority of the proposed algorithm.
3. Aiming at the range migration and the spatial variability of the second Range Compression (SRC) of the bistatic SAR target in the case of large squint, a nonlinear CS (Nonlinear Chirp Scaling Algorithm, NCSA) imaging algorithm for the bistatic SAR target with the same orbit configuration is proposed based on the strict analysis of the two-dimensional spectrum of the bistatic SAR target. For CS imaging algorithm with small squint angle, the nonlinear CS algorithm not only considers the change of modulation frequency with Doppler frequency, but also considers the linear change of modulation frequency with range. It achieves the accurate compensation of SRC in homo-orbital bistatic SAR, and achieves satisfactory focusing effect.
4. For homo-orbital bistatic SAR configurations in spotlight mode, a new frequency scaling (FS) imaging algorithm for homo-orbital bistatic SAR is proposed based on the rigorous analytical method of semi-bistatic angle and spectrum. Firstly, the deramp function for bi-orbital bistatic SAR is derived by analogizing the single-orbital case. The coarse focusing of azimuth can effectively eliminate the aliasing problem in azimuth direction of the system. Then, based on the two-dimensional spectrum of bistatic SAR target, a FS imaging algorithm suitable for spotlight bistatic SAR is proposed to correct the range migration of the target. FS algorithm uses phase multiplication instead of interpolation. The precise bistatic spectrum enables the proposed algorithm to process data in the case of long baseline. Simulation results show the effectiveness of the proposed algorithm. In addition, an improved frequency based on strictly analytic bistatic spectrum is proposed for the space-variant problem of SRC in the case of large squint. Rate-varying scaling algorithm eliminates the range-varying quadratic range compression term caused by large squint by nonlinear scaling operation. Simulation results show that the improved algorithm can achieve good target imaging and the main and side lobes of point target impulse response can be clearly distinguished compared with the conventional FS algorithm.
【學位授予單位】：西安電子科技大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：TN957.52
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