ISAR Multicanale per l'Imaging di Bersagli Terrestri Non-Cooperanti

La presente tesi si inserisce all'interno di un'attività di ricerca svolta presso il Dipartimento di Ingegneria dell'Informazione e relativa allo sviluppo di tecniche e algoritmi utili ai fini di contribuire all'evoluzione del campo del telerilevamento. L’argomento di tesi riguarda inizialmente lo sviluppo di tecniche di cancellazione del clutter di terra per sistemi SAR multicanale. Vengono implementate e simulate tecniche di cancellazione quali la tecnica STAP e la tecnica DPCA. Viene fatto utilizzo, in seguito, dell’analisi tempo/frequenza per determinare con precisione una stima della posizione e della velocità di target in movimento, in una scena osservata sempre da un sistema SAR multicanale, con il fine di effettuare la compensazione del moto dei target stessi all’interno dell’immagine. Successivamente l’attenzione è posta sullo sviluppo di sistemi ISAR multicanale. Viene prima di tutto utilizzata nuovamente l’analisi tempo/frequenza per implementare tecniche di imaging atte a focalizzare bersagli sottoposti a complessi moti di rotazione (manuevering target), e in seguito viene implementato un sistema ISAR multicanale per la soppressione di un forte segnale di disturbo sommato al segnale utile proveniente dal bersaglio in movimento. In conclusione vengono analizzati dati reali acquisiti da un SAR multicanale. Vengono implementate tecniche di coregistrazione e di equalizzazione di immagine per la riduzione del disadattamento tra i canali del sistema stesso e applicata la tecnica DPCA per la riduzione del forte segnale di clutter

Virtual multichannel SAR for ground moving target imaging

Slow moving ground targets are invisible within synthetic aperture radar (SAR) images since they appear defocused and their backscattered signal completely overlap the focused ground return. In order for this targets to be detected and refocused the availability of some spatial degrees of freedom is required. This allows for space/slow time processing to be applied to mitigate the ground clutter. However, multichannel SAR (M-SAR) systems are very expensive and the requirements in terms of baseline length can be very restrictive. In this study a processing scheme that exploits high PRF single channel SAR system to emulate a multichannel SAR is presented. The signal model for both target and clutter components are presented and the difference with respect to an actual M-SAR are highlighted. The effectiveness of the proposed processing is then demonstrated on simulated a measured dataset

Bistatic Space Time Adaptive Processing for Multichannel Inverse Synthetic Aperture Radar Imaging

This thesis mainly focuses on the applications of Inverse Synthetic Aperture Radar (ISAR) processing for high resolution imaging of non-cooperative moving targets observed by a Bistatic Multichannel SAR system. Synthetic Aperture Radar (SAR) is a coherent imaging technique, formulated at the beginning of the 1950s, able to obtain fine resolution images of natural and man-made objects from a long stand off ranges with reduced revisiting time either in all-weather/all-day conditions. Due to these proprieties, SAR systems have been widely used for the environmental monitoring and homeland security applications in the last few decades, making the non-cooperative moving target imaging capability of the system an essential feature. In order to obtain a coherent processing of the echoes received from the scene and to form the synthetic aperture, the illuminated area must be considered static during the observation time. This represents a fundamental drawback since conventional SAR processing is unable to obtain a well-focused image of non-cooperative moving targets which may be possibly present within the observed area. Target defocus is due to the residual motion of the moving target with respect to the static focusing point in the scene. ISAR processing does not base its functioning on the static scene assumption but conversely exploits target own motions for the synthetic aperture formation in order to obtain high cross-range resolution images. Bistatic ISAR system has recently gained attention for its capabilities to overcome some geometrical limitations of monostatic ISAR system and for the developments of some possible applications such as multistatic and passive ISAR imaging. A solution that jointly combine SAR and ISAR processing in order to obtain well focused images of non-cooperative targets in bistatic scenario is analyzed in this thesis. In order to apply ISAR processing to SAR image, targets must be detected first. This step does not represent a particular issue in maritime applications since sea clutter return is lower compared to the target return but, conversely, it can be a critical issue in the case of ground targets embedded in a strong ground clutter that can also be heterogeneous in some real scenarios

Joint physical and virtual STAP for strong ground clutter suppression and imaging

Clutter suppression is a mandatory step in order to detect slow moving targets embedded in strong ground clutter. Multichannel systems allow for sufficient spatial degrees of freedom to be available and as a consequence, allow for STAP processing to be applied. In recent times, a processing scheme that exploits a single channel SAR system with high PRF to emulate a multichannel SAR system is developed. The synthesis of a virtual multichannel SAR system is of considerable importance since it allows for avoiding multiple receiving chains and all the issues related to the cross-channel calibration. The price to be paid is a reduction of the non-ambiguity Doppler region. In this paper a solution that jointly exploits both the virtual and the physical channels of the SAR system is presented. The proposed solution represents a trade-off between the multichannel SAR system complexity and the constraint in radar design caused by the virtualization of a single channel SAR system