【摘要】：逆合成孔徑雷達(dá)(Inverse Synthetic Aperture Radar,ISAR)成像作為一種重要的雷達(dá)成像方式,具有全天候、全天時(shí)、遠(yuǎn)距離對(duì)目標(biāo)進(jìn)行觀測(cè)和定位的能力。傳統(tǒng)的基于傅里葉變換的ISAR成像方法能夠?qū)献鬟\(yùn)動(dòng)目標(biāo)得到較為清晰的目標(biāo)圖像,而對(duì)于非合作運(yùn)動(dòng)目標(biāo),基于傅里葉變換的方法得到的目標(biāo)圖像存在嚴(yán)重的散焦現(xiàn)象。利用時(shí)頻變換(Time-Frequency Transform,TFT)替代傳統(tǒng)的傅里葉變換的方法成像,可以較好的解決由目標(biāo)復(fù)雜運(yùn)動(dòng)導(dǎo)致的圖像散焦問(wèn)題,從而得到較清晰的目標(biāo)圖像。在各類(lèi)時(shí)頻變換方法中,WVD(Wigner-Ville Distribution)擁有較好的的時(shí)頻分辨率,但同時(shí)多分量信號(hào)的WVD變換存在較嚴(yán)重的交叉項(xiàng)干擾問(wèn)題,使得直接利用它進(jìn)行ISAR時(shí)頻成像效果仍不太理想。為了提高成像效果,本文在基于WVD變換的ISAR時(shí)頻成像方法的基礎(chǔ)上,重點(diǎn)研究了利用經(jīng)驗(yàn)?zāi)B(tài)分解降低WVD變換交叉項(xiàng)干擾的方法,并結(jié)合仿真驗(yàn)證了該方法的有效性。在此基礎(chǔ)上進(jìn)一步研究了基于CEMD(Complex Empirical Mode Decomposition)-WVD的ISAR時(shí)頻成像方法,通過(guò)仿真分析可以看出基于CEMD-WVD的ISAR時(shí)頻成像方法在一定程度上抑制了WVD變換的交叉項(xiàng)干擾,使得成像效果有了很大程度的提高。但由于CEMD在對(duì)成像數(shù)據(jù)中的距離單元進(jìn)行分解時(shí)會(huì)產(chǎn)生一定的虛假頻率,會(huì)導(dǎo)致目標(biāo)圖像中任然存在一些虛假的散射點(diǎn)。為了進(jìn)一步提高成像效果,本文分析對(duì)比了BEMD(Bivariate Empirical Mode Decomposition)和CEMD對(duì)多分量信號(hào)的分解能力,發(fā)現(xiàn)BEMD在對(duì)多分量信號(hào)進(jìn)行分解時(shí)產(chǎn)生的虛假頻率更少,能夠更準(zhǔn)確的分解出原信號(hào)中頻率分量,因此本文提出了基于BEMD-WVD的ISAR時(shí)頻成像方法,與基于CEMD-WVD的ISAR時(shí)頻成像方法相比,基于BEMD-WVD的時(shí)頻成像方法產(chǎn)生的虛假散射點(diǎn)更少,成像效果也更理想。同時(shí)受到希爾伯特-黃變換(Hilbert-Huang Transform,HHT)的啟發(fā),本文提出了基于BEMD和瞬時(shí)頻率的ISAR時(shí)頻成像方法,該方法從根本上避免了WVD變換交叉項(xiàng)干擾對(duì)成像效果造成的影響,與基于WVD變換的ISAR時(shí)頻成像方法相比虛假散射點(diǎn)大大減少,成像效果得到顯著的提高,但由于瞬時(shí)頻率的計(jì)算誤差導(dǎo)致成像效果同基于BEMD-WVD的成像方法相比,并沒(méi)有明顯的提高,優(yōu)點(diǎn)是成像速度要明顯快于后者。
[Abstract]:Inverse synthetic Aperture Radar (Inverse Synthetic Aperture Radar,ISAR) imaging, as an important radar imaging method, has the ability to observe and locate the target at a long distance, all weather and all day. The traditional ISAR imaging method based on Fourier transform can get a clear image of the cooperative moving target, but for the non-cooperative moving target, there is a serious defocusing phenomenon in the target image based on the Fourier transform method. Using time-frequency transform (Time-Frequency Transform,TFT) instead of the traditional Fourier transform imaging can solve the defocus problem caused by the complex motion of the target and get a clear target image. WVD (Wigner-Ville Distribution) has good time-frequency resolution in all kinds of time-frequency transform methods, but the WVD transform of multi-component signal has serious crossover interference problem, which makes the direct use of ISAR time-frequency imaging not very ideal. In order to improve the imaging effect, based on the ISAR time-frequency imaging method based on WVD transform, this paper focuses on the method of reducing the cross-term interference of WVD transform by empirical mode decomposition. The effectiveness of the method is verified by simulation. On this basis, the ISAR time-frequency imaging method based on CEMD (Complex Empirical Mode Decomposition) -WVD is further studied. Through the simulation analysis, it can be seen that the ISAR time-frequency imaging method based on CEMD-WVD can restrain the cross-term interference of WVD transform to a certain extent. So that the imaging effect has been greatly improved. However, due to the false frequency generated by CEMD when decomposing the distance unit in the imaging data, there are still some false scattering points in the target image. In order to further improve the imaging effect, the ability of BEMD (Bivariate Empirical Mode Decomposition) and CEMD to decompose multi-component signals is analyzed and compared. It is found that BEMD produces less false frequency when decomposing multi-component signals. The frequency component of the original signal can be decomposed more accurately. Therefore, a ISAR time-frequency imaging method based on BEMD-WVD is proposed. Compared with the ISAR time-frequency imaging method based on CEMD-WVD, the time-frequency imaging method based on BEMD-WVD produces fewer false scattering points. The imaging effect is also better. Inspired by Hilbert-Huang transform (Hilbert-Huang Transform,HHT), a ISAR time-frequency imaging method based on BEMD and instantaneous frequency is proposed in this paper. The method avoids the influence of the cross-term interference of WVD transform on the imaging effect. Compared with the ISAR time-frequency imaging method based on WVD transform, the false scattering points are greatly reduced, and the imaging effect is greatly improved. However, because of the calculation error of instantaneous frequency, the imaging effect is not obviously improved compared with the method based on BEMD-WVD. The advantage is that the imaging speed is much faster than the latter.
【學(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TN957.52

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