This paper presents a customized three-dimensional template matching technique for autonomous pose determination of uncooperative targets. This topic is relevant to advanced space applications, like active debris removal and on-orbit servicing. The proposed technique is model-based and produces estimates of the target pose without any prior pose information, by processing three-dimensional point clouds provided by a LIDAR. These estimates are then used to initialize a pose tracking algorithm. Peculiar features of the proposed approach are the use of a reduced number of templates and the idea of building the database of templates on-line, thus significantly reducing the amount of on-board stored data with respect to traditional techniques. An algorithm variant is also introduced aimed at further accelerating the pose acquisition time and reducing the computational cost. Technique performance is investigated within a realistic numerical simulation environment comprising a target model, LIDAR operation and various target-chaser relative dynamics scenarios, relevant to close-proximity flight operations. Specifically, the capability of the proposed techniques to provide a pose solution suitable to initialize the tracking algorithm is demonstrated, as well as their robustness against highly variable pose conditions determined by the relative dynamics. Finally, a criterion for autonomous failure detection of the presented techniques is presented.

A new algorithm for ship wake detection is developed with the aim of ship heading and velocity estimation. It exploits the Radon transform and utilizes merit indexes in the intensity domain to validate the detected linear features as real components of the ship wake. Finally, ship velocity is estimated by state-of-the-art techniques of azimuth shift and Kelvin arm wavelength. The algorithm is applied to 13 X-band SAR images from the TerraSAR-X and COSMO/SkyMed missions with different polarization and incidence angles. Results show that the vast majority of wake features are correctly detected and validated also in critical situations, i.e., when multiple wake appearances or dark areas not related to wake features are imaged. The ship route estimations are validated with truth-at-sea in seven cases. Finally, it is also verified that the algorithm does not detect wakes in the surroundings of 10 ships without wake appearances.

This paper presents an application of the European Remote Sensing (ERS) satellites' radar data to digital elevation model (DEM) generation. The selected test site is the Sannio-Matese area in southern Italy, where several corner reflectors (CRs) were deployed to be used as ground control points (GCPs) for height measurement accuracy validation. First of all, an analysis of the CR response in radar images is presented. Then, the procedure for image pair geometric registration and interferogram formation is described in detail. A quantitative analysis is also performed by comparing these interferograms to the corresponding products obtained by using the ISAR software, officially distributed by the European Space Agency (ESA). Reported correlation values show that only tandem pairs allow an efficient interferometric processing to be performed, thanks to their short-time baseline (one day), whereas correlation adequate for differential interferometry could not be achieved. The method adopted for the computation of the interferometric baseline components on the basis of satellite orbital data is described, including the GCP-based corrections. The procedure was applied to obtain DEMs of a 10×10 km2 subarea characterized by very high correlation coefficients (0.6). The best attained values of the GCP height measurement accuracy were about 4 m. Finally, the DEMs were compared, giving root mean square (rms) differences less than 20 m in the best case

A system study of a spaceborne along-track synthetic aperture radar (SAR) interferometer is presented. This sensor has been successfully experienced for detecting moving targets by using only airborne installations. Several key issues must be addressed when spaceborne configurations are envisaged. To this end, a quantitative evaluation of system performance and measurement accuracy has been conducted. First, the identification of possible space configurations has been accomplished. In particular, the two antennas can operate on a single satellite or they can be carried along appropriate trajectories by two spacecrafts. Then, an error budget of radial velocity measurement accuracy has been performed. Finally, two possible mission scenarios are dealt in details, and numerical results are reported.