Search

We propose a novel despeckling algorithm for synthetic aperture radar (SAR) images based on the concepts of nonlocal filtering and wavelet-domain shrinkage. It follows the structure of the block-matching 3-D algorithm, recently proposed for additive white Gaussian noise denoising, but modifies its major processing steps in order to take into account the peculiarities of SAR images. A probabilistic similarity measure is used for the block-matching step, while the wavelet shrinkage is developed using an additive signal-dependent noise model and looking for the optimum local linear minimum-mean-square-error estimator in the wavelet domain. The proposed technique compares favorably w.r.t. several state-of-the-art reference techniques, with better results both in terms of signal-to-noise ratio (on simulated speckled images) and of perceived image quality. [ABSTRACT FROM AUTHOR]

This paper presents the trajectory control strategies for the de-orbiting and re-entry phases of a micro satellite equipped with a deployable and controlled aero-brake. They are framed in the design of the Italian space mission MISTRAL (MIcro-SaTellite with Air-Launchable Re-entry capabilities) developed under the supervision of the DAC-Campanian Aerospace District. The proposed control approach makes use of two different control strategies for the de-orbiting and re-entry phases, respectively. The former is based on a linear quadratic optimal control, whereas the latter is based on a model predictive control approach. Numerical simulation results demonstrate the effectiveness of the proposed approach which guarantees a good compromise between stability and performance during the mission phases of interest. • A control strategy for the de-orbiting and re-entry phase of a micro-satellite using a deployable aero-brake is proposed. • An LQR-based approach with state feedback is used for the de-orbiting phase. • An MPC approach with a terminal cost on the prediction time horizon is used for the re-entry phase. • Performance is assessed numerically by modelling both the entire GNC system and the satellite dynamics. • The achieved tracking error is compatible with the required landing accuracy of 250 km. [ABSTRACT FROM AUTHOR]