We propose a calibration method suitable for a set of repeated synthetic aperture radar (SAR) acquisitions that uses both absolute calibrated devices (such as corner reflectors) and stable targets identified in the scene [the permanent scatterers (PSs)]. Precisely, the role of the PS is to extend the initial calibration sequence by monitoring the radiometric stability of the system throughout the whole mission life span. At a first step, this paper approaches the problem of PS-based normalization by an iterative maximum-likelihood method that exploits the stack of complex interferometric SAR images. Two solutions are given based on different assumptions on the PS phases. As a second step, the merging of these estimates with the available calibration information is discussed. Results achieved by experimental acquisitions are shown in two different SAR systems: 1) a C-band spaceborne SAR and 2) a Ku-band ground-based SAR
In spaceborne synthetic aperture radars (SARs), the orbit curvature may prevent the use of the ωk processor, causing artifacts that depend on both the extent of the orbit arc and the slant range interval. A viable solution has been derived by extending the singular value decomposition-Stolt approach that was proposed for geophysical applications to microwave SAR. The resulting processor has the same simple scheme as the ωk approach but a different (numerical) computation of both the reference and the Stolt interpolation.
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.
The paper proposes a method to estimate 2D/3D vibrations and displacements of mostly linear structures, like pipes, chimneys, towers, bridges from afar, based on synchronized Radars. The method takes advantage of Radar sensitivity to displacements to sense tiny deformations (up to tens of micron) with a time scale from milliseconds to hours. The key elements are: (a) The use of calibrators to remove at once both the tropospheric turbulence and the effect of radial motion, and (b) the compensation of interferences from fixed targets. The latter is performed by estimating and removing the contribution of interfering targets, based either on a proper data processing or by exploiting an ad-hoc motorized calibrator. Performance in terms of accuracy of the deformation field is evaluated theoretically and checked by tests carried out in laboratories and by full-scale acquisition campaigns.
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