Synthetic aperture radar (SAR) has become an important technique for generating high-resolution images of the ground because of its all-weather capabilities. SAR imaging of stationary scenes is nowadays well mastered. Moving targets induce a delocalization and a defocusing effect in the azimuth direction in a SAR image. This latter effect can be used to detect moving targets, to image them, and to estimate their azimuthal velocity, but the main limitation is the impossibility to estimate the full target velocity vector, because of the Doppler shift dependence on azimuthal position and radial velocity. In this paper, we analyze the performances of a method that reconstructs the real target trajectory given the apparent positions of the moving target measured on SAR images acquired along a circular trajectory. We first outline the steps of this trajectory reconstruction methodology, then we perform a mathematical analysis of this methodology, and finally, we present some results on real data, around two French cities.

/pdf/ground-moving-target-trajectory-reconstruction-in-single-bqjvpbbspj.pdf

Ground Moving Target Trajectory Reconstruction in Single-Channel Circular SAR

: A new theory and algorithm for scatterer classification in SAR imagery is presented. The automated classification process is operationally efficient compared to existing image segmentation methods requiring human supervision. The algorithm reconstructs coarse resolution subimages from subdomains of the SAR phase history. It analyzes local peaks in the subimages to determine locations and geometric shapes of scatterers in the scene. Scatterer locations are indicated by the presence of a stable peak in all subimages for a given subaperture, while scatterer shapes are indicated by changes in pixel intensity. A new multi-peak model is developed from physical models of electromagnetic scattering to predict how pixel intensities behave for different scatterer shapes. The algorithm uses a least squares classifier to match observed pixel behavior to the model. Classification accuracy improves with increasing fractional bandwidth and is subject to the high-frequency and wide-aperture approximations of the multi-peak model. For superior computational efficiency, an integrated fast SAR imaging technique is developed to combine the coarse resolution subimages into a final SAR image having fine resolution. Finally, classification results are overlaid on the SAR image so that analysts can deduce the significance of the scatterer shape information within the image context.

/pdf/phase-history-decomposition-for-efficient-scatterer-2dete1en6j.pdf

Phase history decomposition for efficient scatterer classification in SAR imagery

The problems about the detection of moving objects and observation by the synthetic aperture radars(SAR) are described in this paper.It also explains the moving target indication(MTI) SAR approach using the reflectivity displacement method,the MTI SAR aproach using the multilook image displacement method,and the MTI SAR approach using more than one antenna along the flight direction and an adaptive space time filtering to maximize signal to disturbance ratio.The position and the velocity estimation of moving objects on the ground are also discussed.

Synthetic aperture radar and moving target indication

L’imagerie RSO circulaire aeroportee permet d’obtenir de nombreuses informations sur les zones imagees et sur les cibles mobiles. Les objets peuvent etre observes sous plusieurs angles, et l’illumination continue d’une meme scene permet de generer plusieurs images successives de la meme zone. L’objectif de cette these est de developper une methode de reconstruction de trajectoire de cibles mobiles en imagerie RSO circulaire monovoie, et d’etudier les performances de la methode proposee. Nous avons tout d’abord mesure les coordonnees apparentes des cibles mobiles sur les images RSO et leur parametre de defocalisation. Ceci permet d’obtenir des informations de mouvement des cibles, notamment de vitesse et d’acceleration. Nous avons ensuite utilise ces mesures pour definir un systeme d’equations non-lineaires permettant de faire le lien entre les trajectoires reelles des cibles mobiles et leurs trajectoires apparentes. Par une analyse mathematique et numerique de la stabilite de ce systeme, nous avons montre que seul un modele de cible mobile avec une vitesse constante permet de reconstruire precisement les trajectoires des cibles mobiles, sous reserve d’une excursion angulaire suffisante. Par la suite, nous avons etudie l’influence de la resolution des images sur les performances de reconstruction des trajectoires, en calculant theoriquement les precisions de mesure et les precisions de reconstruction qui en decoulent. Nous avons mis en evidence l’existence theorique d’une resolution azimutale optimale, dependant de la radiometrie des cibles et de la validite des modeles etudies. Finalement nous avons valide la methode developpee sur deux jeux de donnees reelles.

Reconstruction de trajectoires de cibles mobiles en imagerie RSO aéroportée

L'imagerie RSO circulaire aeroportee permet d'obtenir de nombreuses informations sur les zones imagees et sur les cibles mobiles. Les objets peuvent etre observes sous plusieurs angles, et l'illumination continue d'une meme scene permet de generer plusieurs images successives de la meme zone. L'objectif de cette these est de developper une methode de reconstruction de trajectoire de cibles mobiles en imagerie RSO circulaire monovoie, et d'etudier les performances de la methode proposee. Nous avons tout d'abord mesure les coordonnees apparentes des cibles mobiles sur les images RSO et leur parametre de defocalisation. Ceci permet d'obtenir des informations de mouvement des cibles, notamment de vitesse et d'acceleration. Nous avons ensuite utilise ces mesures pour definir un systeme d'equations non-lineaires permettant de faire le lien entre les trajectoires reelles des cibles mobiles et leurs trajectoires apparentes. Par une analyse mathematique et numerique de la stabilite de ce systeme, nous avons montre que seul un modele de cible mobile avec une vitesse constante permet de reconstruire precisement les trajectoires des cibles mobiles, sous reserve d'une excursion angulaire suffisante. Par la suite, nous avons etudie l'influence de la resolution des images sur les performances de reconstruction des trajectoires, en calculant theoriquement les precisions de mesure et les precisions de reconstruction qui en decoulent. Nous avons mis en evidence l'existence theorique d'une resolution azimutale optimale, dependant de la radiometrie des cibles et de la validite des modeles etudies. Finalement nous avons valide la methode developpee sur deux jeux de donnees reelles acquises par le capteur SETHI et RAMSES NG de l'ONERA en bande X, et confirme les analyses theoriques des performances de cette methode.

https://tel.archives-ouvertes.fr/tel-01002732/document

Reconstruction de trajectoires de cibles mobiles en imagerie RSO circulaire aéroportée

In this work, we examine ground target detection and characterization from radar data, which incorporates a modelbased optimization method called dynamic logic (DL). We apply our methodology to a prototype airborne radar platform called Gotcha, developed by the Air Force Research Laboratory/Sensors Directorate/Automatic Target Recognition Division in recent years. The aircraft traces out a circular path around an area of interest, and the onboard, side-looking radar transmits and receives energy at a constant pulse repetition frequency, while the main beam direction is maintained at a fixed aim point on the ground. Data collected during any appropriate length arc of the flight path can be used to create synthetic aperture radar (SAR) images of the ground. The data can also be used for ground moving target indication (GMTI) and provide Doppler/Range imagery of the same ground area. Our approach combines the computation of Range-Doppler surfaces and a variable target velocity backprojection SAR method. Potential targets are detected using multiple backprojection images and features are extracted using adaptive mixture models. We demonstrate the feasibility of our approach using target truth information provided with the Gotcha dataset. We outline the steps toward implementing a comprehensive automatic target tracking solution based on presented methodology.

/pdf/moving-target-detection-and-characterization-with-circular-20ioujujzy.pdf

Moving target detection and characterization with circular SAR

In this paper, we apply Dynamic Logic algorithm (DL) directly to analyze AFRL Gotcha raw data, which are sampled in
terms of chirp frequencies for each pulse. This approach has not been done in the existing literature because previously,
there is no visual or conceptual interpretation how to detect ground moving targets directly from synthetic aperture radar
(SAR) raw data. Using Gotcha raw data taken from the severe radar clutter environment, we have demonstrated that DL
not only maintains its robustness in terms of detecting small ground moving targets but also provides the effectiveness to
extract specific features such as shape, size, location (along the range swath), movement direction, and traveling speed
for the desired target.

Freeman C. Lin

Papers

Moving target detection and characterization with circular SAR

Application of dynamic logic algorithm to analyze AFRL gotcha data