Study On Inverse Synthetic Aperture Radar Imaging Methods

Inverse synthetic aperture radar (ISAR) is a high-resolution imaging radar that canobtain high-resolution images of non-cooperative targets all day and night under allweather from long range (such as planes, missiles, ships, etc.), which has good applicationprospects in military and civil applications. The key technologies of ISAR involve motioncompensation, imaging algorithms, cross-range scaling of ISAR images and so on. Thesetechnologies are still needs to be improved. Therefore, ISAR technology should be deeplystudied continuously. This paper mainly studies ISAR imaging methods and cross-rangescaling of ISAR images, imaging targets including aircrafts and ships.Chapter1is the introduction. Firstly, the research background, significance anddevelopment of ISAR are introduced. Then, the basic principles of ISAR imaging andISAR signal processing technology are reviewed. Lastly, the main contents of this thesisare presented.In chapter2, the problem of how to select the optimal ship imaging time is discusseddeeply. A method for optimal imaging instant is presented based on Doppler centroidestimation and the optimal imaging duration is searched out by maximizing the imagecontrast. In high sea states, approximate side-view ship images are obtained by exploitingthe ship’s own motion. In low sea states, approximate top-view ship images are obtained byexploiting the movement of the radar platform or radar carrier. Simulations are performedto verify the effectiveness of this method.In chapter3, multistatic ISAR imaging method for ship targets is studied, which iscapable of increasing the integration time of stationary imaging as compared to themonostatic radar by deploying the multiple platforms with appropriate altitudes and aspectangles and coherently integrating the echoes received by each platform. Combined with theoptimal imaging time selection scheme, this method can obtain high-resolution side-viewor top-view ship images. Simulations are performed to verify the effectiveness of ourmultistatic ISAR ship imaging method.In chapter4, an imaging method based on compressed sensing (CS) using sparse ISARdata is proposed. For the sparse aperture echo data, the traditional range-Doppler (RD)imaging algorithm has serious side-lobes. When the sparsity is large, ISAR images can’t beobtained. In this method, Gaussian test is first used to select the range bins that containscatterers and a sparse basis dictionary and linear measurement matrix are constructed.Then the convex optimization means as the orthogonal matching pursuit (OMP) is used toextract the scatter amplitude and location information. By all the steps above, the image ofISAR is formed in the RD domain. No interpolation is needed for the sparse aperture, andno sidelobes exit in ISAR images. Processing of the real sparse ISAR data verifies thefeasibility and superiority of the approach.In chapter5, the ISAR imaging for the maneuvering targets is studied. The Doppler frequency of these targets is time-varying, so the traditional RD imaging algorithm willlead to unfocused images. In this method, the statistical characteristic of background noiseand clutters is investigated, and then Gaussian test is performed to all range cells by usingthe presetting desired probability of the false rate. Finally, scatterers are extracted by theCLEAN method and a high resolution ISAR image is generated. Real data processingresults indicate that our method has better performance than the traditional RD method.In chapter6, the problem of cross-range scaling of ISAR is addressed. A techniquebased on the multiple dominant scatterers synthesis is used to estimate the chirp rate, thenestimating the rotation velocity by analyzing the relation between the chirp rate of thecross-range signal and the range cell by least square error (LSE) method. Compared withexisting methods, this method combines the information of multiple dominant scatterers,and does not require a threshold. Finally, simulation and experimental data processingresults show the effectiveness of the method.In chapter7, the work of the whole thesis is concluded and the issues to be furtherstudied are pointed out as well.