Browsing by Subject "Synthetic aperture radar."

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Open Access
Methods for target detection in SAR images
(2009) Duman, Kaan
Automatic recognition and classification of man-made objects in SAR (Synthetic Aperture Radar) images have been an active research area because SAR sensors can produce images of scenes in all weather conditions at any time of the day which is not possible with infrared and optical sensors [1, 2]. In this thesis, different feature parameter extraction methods from SAR images are proposed. The new approach is based on region covariance (RC) method which involves the computation of a covariance matrix of a ROI (region of interest). Entries of the covariance matrix are used in target detection. In addition, the use of computationally more efficient region codifference matrix for target detection in SAR images is also introduced. Simulation results of target detection in MSTAR (Moving and Stationary Target Recognition) database are presented. The RC and region codifference methods deliver high detection accuracies and low false alarm rates. The performance of these methods is investigated with various distance metrics and Support Vector Machine (SVM) classifiers. It is also observed that the region codifference method produces better results than the commonly used Principle Component Analysis (PCA) method which is used together with SVM. The second part of the thesis offers some techniques to decrease the computational cost of the proposed methods. In this approach, ROIs are filtered by directional filters (DFs) at first as a pre-processing stage. Images are categorized according to the filter outputs. The proposed RC and codifference methods are applied within the categories determined by these filters. Simulation results of target detection in MSTAR database are presented through decisions made with l1 norm distance metric and SVM. The number of comparisons made with the training images using l1 norm distance measure decreases as these images are distributed into categories. Therefore, the computational cost of the previous algorithm is significantly reduced. SAR image classification results based on l1 norm distance metric are better than the results obtained using SVM and they show that the two-stage approach does not reduce the performance rate of the previously proposed method much, especially when codifference features are used.
Open Access
Novel methods for SAR imaging problems
(2013) Uğur, Salih
Synthetic Aperture Radar (SAR) provides high resolution images of terrain reflectivity. SAR systems are indispensable in many remote sensing applications. High resolution imaging of terrain requires precise position information of the radar platform on its flight path. In target detection and identification applications, imaging of sparse reflectivity scenes is a requirement. In this thesis, novel SAR image reconstruction techniques for sparse target scenes are developed. These techniques differ from earlier approaches in their ability of simultaneous image reconstruction and motion compensation. It is shown that if the residual phase error after INS/GPS corrected platform motion is captured in the signal model, then the optimal autofocused image formation can be formulated as a sparse reconstruction problem. In the first proposed technique, Non-Linear Conjugate Gradient Descent algorithm is used to obtain the optimum reconstruction. To increase robustness in the reconstruction, Total Variation penalty is introduced into the cost function of the optimization. To reduce the rate of A/D conversion and memory requirements, a specific under sampling pattern is introduced. In the second proposed technique, Expectation Maximization Based Matching Pursuit (EMMP) algorithm is utilized to obtain the optimum sparse SAR reconstruction. EMMP algorithm is greedy and computationally less complex resulting in fast SAR image reconstructions. Based on a variety of metrics, performances of the proposed techniques are compared. It is observed that the EMMP algorithm has an additional advantage of reconstructing off-grid targets by perturbing on-grid basis vectors on a finer grid.