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Study Of Motion Compensation, Narrow Band Interference Suppression And Single Channel GMTI Of Airborne SAR

Posted on:2008-03-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:F ZhouFull Text:PDF
GTID:1118360272978180Subject:Signal and Information Processing
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After fifty years' development, the fundamentals and the key algorithms of synthetic aperture radar (SAR) imaging have been improved greatly. However, as SAR has been applied to military and civil fields extensively, this technique will face many new problems and challenges. For example, the motion error of Radar platform may add difficulty to SAR imaging and thus causes image defocusing, especially when the inertia navigation system (INS) of airborne SAR is limited. Therefore, the research on raw data based motion compensation is of great significance in domestic SAR imaging. On the other hand, the existence of narrow band interference (NBI) will decrease the signal-interference ratio dramatically, so research on the algorithm of estimating and prohibiting narrow band interference can increase SAR imaging quality effectively. In addition, the moving target in the scene may exhibit defocusing or shifting, so how to locate and image them accurately has become a hotspot in SAR research field. This dissertation represents detailed research on airborne SAR motion compensation, suppression of NBI and SAR ground moving target detection, based on conceptual analysis, theory derivation and data validation. The main contents are summarized as follows:1. Two valid algorithm, Range-Doppler (R-D) and chirp scaling (CS) algorithm are discussed in detail. The R-D algorithm compensates for the range curvature in Doppler domain while adjusts range walk in slow time domain. It can be applied not only to broadside SAR imaging, but also to high squint SAR imaging. The CS algorithm can be applied to broadside SAR and low squint SAR imaging with high resolution.2. The motion compensation of airborne SAR is researched systematically. Based on the geometric model and empirical formulas, this paper analyses the control requirements of SAR system on motion error and introduces a motion compensation method based on the measuring system. Then an effective airborne SAR motion compensation program is proposed according to the analysis of SAR system's motion error. In this approach, the attitude errors are compensated through the two- dimensional antenna servo system and translational errors are estimated by the instantaneous Doppler chirp rate in the echo data. Then, the translational errors are compensated through envelope correction and phase correction.3. A motion compensation method applied to high squint SAR is proposed. Based on the established imaging geometry of high squint SAR, the relationship between motion compensation and Doppler parameters has been analyzed and deduced. Meanwhile, the components of motion errors are estimated with pseudo-inverse technique in virtue of instantaneous Doppler chirp rate and partial airborne INS parameters. Then effective motion compensation is implemented to raw data according to the acquired motion errors.4. Single channel ground moving target detection and imaging is investigated systematically. A new approach to ground moving target detection, based on two-look processing, is proposed for single channel SAR system. This approach can be applied to the detection of moving target with radial velocity under low signal-to-clutter ratio (SCR). In this approach, the Doppler spectra of echoes are separated into two parts and are focused separately to obtain two sub-images. Then by matching the two sub-images and implementing non-coherent cancellation, the ground clutters are suppressed and hence the moving target detection ability is increased, according to the Doppler spectra shifts of moving targets relative to that of a stationary scene. In addition, windows are added to SAR images to get complex signals of the moving target and to calculate the translational shifts of the Doppler spectra relative to that of the stationary scene. In this way, the ground moving target can be located precisely and the false warning probability can be decreased greatly.5. A method on ground moving target parameter estimation and precise imaging is proposed, which can be applied to high signal-to-clutter ratio. Based on the characteristics of envelopes and the Doppler frequency spectrum of the echoes, a new method is proposed. Firstly, a second-order generalized keystone formatting algorithm is used to compensate for the range curvature. Secondly, the estimated slope of the target echo's envelope is used for range walk compensation. Thirdly, Doppler parameters of moving targets obtained via spectral analysis are used for the imaging and positioning of ground moving targets. Finally, motion parameters of moving targets can be estimated based on the relationship between Doppler and motion parameters.6. Analyzes the characteristics of the common Narrow Band Interference (NBI) systematically. A method which uses eigen-subspace based filtering on the echo data is proposed. It determines the nature of NBI in the frequency domain and implements adaptive NBI suppression in the temporal domain, which constructs interference subspace from the raw data and then subtracts the projected components of the original data onto the interference subspace. It is a nonparametric approach and is more robust than the conventional modeling based approaches. 7. A parameterized NBI Suppression method based on improved LMS algorithm is proposed. Firstly, the frequencies of NBI are obtained by Pisarenko harmonic analysis. Secondly, the complex envelopes of NBI are estimated by implementing the LMS algorithm segmentally and by applying data interpolation. Finally, the suppression of NBI is accomplished by time domain cancellation and signal gain recovery of the data.
Keywords/Search Tags:Airborne synthetic aperture radar (SAR), motion compensation, high squint SAR, narrow band interference (NBI) suppression, motion parameter estimation, ground moving target indication (GMTI)
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