Fully-focusing of radar altimeters is a recent concept that has been introduced to allow further improvement of along-track resolution in high pulse repetition frequency (PRF) radar altimeters. The straight potentiality of this new perspective reflects into a more accurate estimation of geophysical parameters in some applications such as sea-ice observation. However, as documented in a recent paper, such capability leaves unsolved the problem of the high computational effort required. In this paper, we face the problem of adapting for altimeters the Omega-Kappa SAR focusing algorithm that is performed in the two-dimensional wavenumber domain, accounting for the difference existing between SAR and altimeter from geometry (looking and swath width) and instrument (echoes are deramped onboard on receiving) point of view. Simulations and an application using in-orbit data show the effectiveness of the proposed approach and the highly reduced computational effort.

A spaceborne SAR is proposed, aimed at global monitoring with a short revisit time (12 days). Such a system is not feasible in a conventional STRIPMAP mode, due to the known relation between range coverage and azimuth antenna length. However, it can be achieved in burst mode SARs, like ScanSAR and TOPSAR. We detail the design of ScanSAR and TOPSAR sensors, we provide a scheme to optimize the burst length in TOPSAR, and finally we discuss an innovative burst-mode scheme, defined as TOPS-SPOT. The performances of the three schemes are analyzed in terms of scalloping, Noise Equivalent Sigma Zero (NESZ), and ambiguities and are validated with simulated results achieved by assuming point targets on the ellipsoidal earth. Résumée. Nous proposons un système SAR envisagé pour l'observation globale du planète avec un temps de révisite très court (12 jours). La système ne serait pas faisable avec la technique STRIPMAP dès qu'il y a une relation bien précise entre la longueur de l'antenne et la couverture en range. Toutefois, on pourrait bien utiliser des techniqueá poussées d'activité (bursts), comme les techniques SCANSAR où TOPSAR. Nous détaillons le projet des senseurs SCANSAR et TOPSAR, nous optimisons la longueur des poussées d' activité et nous présentons une nouvelle méthode que nous appelons TOPSSPOT. Les performances de ces trois techniques sont analysées en termes de scalloping, Noiseéquivalent sigma zéro, et ambiguïtés et elle sont validées avec une simulation avec des balises disposées sur une terre ellipsoïdale.

R ADAR polarimetry allows the collection of a significant wealth of information, with respect to single-channel synthetic aperture radar (SAR) sensors, at the expense of greater system complexity. Polarimetric calibration is a necessary preprocessing step for the correction of distortion interference due to system inaccuracies and atmospheric effects.The problem can be approached from two different application angles: by a system monitoring viewpoint, when the estimation of system distortion parameters such as crosstalks (CTs) and channel imbalances (CIs) is targeted, and by an image calibration standpoint, where the efforts are not aimed at retrieving the parameters, rather at removing the joint distortion effect on the data. In either case, it is necessary to rely on some reference calibrator. Both the use of distributed targets (DTs) alone and in combination with one or more calibrators, such as trihedral corner reflectors (CRs) and polarimetric active radar calibrators (PARCs), have been considered in the literature [1]-[3]. The former solution would appear as the most convenient one since it avoids the deployment of artificial reflectors. However, the limited amount of information provided by a DT Manuscript

The paper analyses an along-track multistatic Synthetic Aperture Radar (SAR) formation. The formation aims at achieving a high azimuth resolution maintaining at the same time a large swath width. The case with one transmitting sensor and all receiving is analyzed (Single Input Multiple Output, SIMO). An effective and novel reconstruction, in the two-dimensional frequency domain is introduced that is able to keep low the azimuth ambiguity and achieve a recombination gain close to the theoretical one. Degradation of the system performance due to the loss of the control of formation position is analyzed using probabilistic considerations. Moreover, some innovative methods to mitigate the loss of optimality are introduced and evaluated using simulations. Finally, considerations on the impact of the across-track non zero baseline are discussed.

No abstract

Abstract:We propose the use of Sentinel-1 Synthetic Aperture Radar (SAR) to provide a continuous and global monitoring of Radio Frequency Interferences (RFI) in C-band. We take advantage of the first 8-10 echo measures at the beginning of each burst, a 50-70 MHz wide bandwidth and a ground beam coverage of~25 km (azimuth) by 70 km (range). Such observations can be repeated with a frequency better than three days, by considering two satellites and both ascending and descending passes. These measures can be used to qualify the same Sentinel-1 (S1) dataset as well as to monitor the availability and the use of radio frequency spectrum for present and future spaceborne imagers and for policy makers. In the paper we investigate the feasibility and the limits of this approach, and we provide a first Radio Frequency Interference (RFI) map with continental coverage over Europe.

The paper addresses the temporal stability of distributed targets, particularly referring to vegetation, to evaluate the degradation affecting synthetic aperture radar (SAR) imaging and repeat-pass interferometry, and provide efficient SAR simulation schemes for generating big dataset from wide areas. The models that are mostly adopted in literature are critically reviewed, and aim to study decorrelation in a range of time (from hours to days), of interest for long-term SAR, such as ground-based or geosynchronous, or repeat-pass SAR interferometry. It is shown that none of them explicitly account for a decorrelation occurring in the short-term. An explanation is provided, and a novel temporal decorrelation model is proposed to account for that fast decorrelation. A formal method is developed to evaluate the performance of SAR focusing, and interferometry on a homogenous, stationary scene, in terms of Signal-to-Clutter Ratio (SCR), and interferometric coherence. Finally, an efficient implementation of an SAR simulator capable of handling the realistic case of heterogeneous decorrelation over a wide area is discussed. Examples are given by assuming two geostationary SAR missions in C and X band.

No abstract