Study Of Imaging Algorithms For Tandem Bistatic SAR

Different from the traditional monostatic synthetic aperture radar (SAR), the transmitterand the receiver are amounted on different platforms for bistatic SAR (BiSAR). They can beset to have different space positions and velocities. Hence BiSAR has a plenty of potentialsand advantages over monostatic SAR in many application areas, such as the militaryapplications, resource investigation, surveillance of Earth crust, etc. Among the bistaticconfigurations, tandem bistatic SAR confguraton, in which the transmitter and the receivertravel along the same track with the same velocity, is a special one. Compared with otherbistatic configurations, the formation of tandem configuration is a relatively easy one, whichhas a bright future in ground moving target indication (GMTI). Moreover, it is also relativelyeasy to be accomplished in engineering. Due to the advantages of tandem bistatic SAR, theprecision of the two-dimensional point target spectrum and the imaging algorithms suitablefor different modes of tandem bistatic SAR are studied in this dissertation, the main works aresummarized as follows:1. Loffeld’s bistatic forumula is suitable for any bistatic configuration. However, theprecision of the LBF spectrum is different in different configurations under differentparameters. Focusing of the well-known tandem configuration of bistatic SAR, the twofactors that influence the precision of the LBF spectrum is deduced and analyzed bycomparing the LBF spectrum with an exactly analytical point target spectrum in thewavenumber domain. The first factor is how the value of the cosine of the half bistatic angleis close to1, and the second factor is whether the half length of the baseline to range ratioequals the tangent of the half bistatic angle. When the two factors are both satisfied, the LBFsectrum is an exact analytical one. And among the two factors that influence the precison ofthe spetrum, the LBF spectrum is more sensitive to the variance of the cosine of the halfbistatic angle. The length of the baseline or the squint angles of bistatic SAR does not give adirect influence to the precision of the spectrum. The factors that influence the precision ofthe LBF spectrum are verified by simulations.2. Focusing of the profile range dependent problem of tandem bistatic SAR, achirp-scaling (CS) imaging algorithm is proposed based on an exact analyticaltwo-dimensional point target spectrum. Different from the imaging algorithms in thewavenumber domin, no interpolation is needed during the whole imaging process. Fastimaging is implemented in the frequency domain. Due to the high precision of thetwo-dimensional point target spectrum that we are based on, the proposed algorithm is notsensitive to the length of the baseline. It is capable of handling the tandem bistatic SAR data with a large bistatc angles or with a large baseline. Simulations and comparable experimentsvalidate the effectiveness and advantages of the proposed algorithm.3. Focusing of the range dependent problem of the range migration and the second rangecompression (SRC) of tandem bistatic SAR with high squint angles, based on an exactanalytical two-dimension point target spectrum, a nonlinear chirp-scaling imaging algorithm(NCSA) is proposed. Different from the chirp-scaling algorithm suitable for small squintangles, not only the Doppler dependence of the Doppler chirp rate is considered, but also thevariance with range of the Doppler chirp rate is taken into account in the proposed algorithm.Precise compensation of the SRC is realized, and satisfying imaging result is obtained. Theeffectiveness of the proposed algorithm is verified by simulations.4. Focusing of the spotlight mode of tandem bistatic SAR, a frequency scaling (FS)imaging algorithm is proposed based on an exact analytical half bistatic angle and thespectrum analysis method. Firstly, on analog of the monostatic case, the deramping functionsuitable for bistatic SAR is deduced, and coarse focusing in azimuth is realized, then the FSalgorithm is carried out to correct the range migration of different range gates, and finalimaging resuls with satisfactory are obtained. Range migration correction is realized by phasemultiplication instead of interpolation, fast imaging process is realized in the proposedalgorithm. The proposed algorithm is capable of dealing with bistatic SAR data with largebaselines of tadem configuration. Simulations verify the effectiness of the proposed algorithm.Moreover, a modified frequency scaling imaging algorithm is proposed to handle the largesquint angle case, in which the range dependence of the second range compression must betaken into consideration. Compared with the FS algorithm, the modified frequency scalingalgorithm can realize satisfying focusing with large squint angles. The main lobe andsidelobes of the impulse response of the point target can be well-resolved.