Fabio Rocca

Methods for measuring small displacements of television images

Various techniques are described to measure, small displacements of television images. If two successive video frames are considered, their differences are approximately a linear combination of the components of the displacement of the object. If all the points of the frame undergo the same movement, then the velocity estimation problem is solved using linear estimation. However, if some points belong to the moving object and the others to the background, the problem can be stated in the same way only if an algorithm is available to segment the image into fixed and moving areas. Afterwards, linear estimation can be applied to the moving area only. In this paper a segmentation algorithm is proposed which uses dynamic programming (Viterbi algorithm with three states). A more complex situation arises when the points belonging to the moving area are subjected to different movements. The problem can be solved once more using dynamic programming if the displacement components are quantized into (2M + 1) (2M + 1) values, and the number of states of the Viterbi algorithm is augmented to (2M + 1)^{2} . To reduce the technical difficulties of this approach, a simpler method that makes possible the estimation of the n most probable displacements is proposed. Then the image is segmented into n moving areas with different displacements and a background area using a Viterbi algorithm with n + 1 states. Experimental results show that the precision obtainable is about 0.1 pel when the displacements are up to 2-3 pels, the object had approximate dimensions of 90 \times 90 pels, and the signal-to-noise ratio was higher than 33 dB.

Analysis of Permanent Scatterers in SAR interferometry

In previous papers, it has been shown that stable and pointwise targets (Permanent Scatterers) can be identified from long temporal series of ERS SAR images. On the PS grid, all data can be exploited for displacement estimation, regardless of their temporal and geometrical baselines. In this paper, it will be shown how a first selection of PS (a key step in the PS technique) can be carried out by means of a statistical analysis of the amplitude time series, after radiometric correction. An example of this incoherent approach to PS candidates selection will be illustrated and discussed. The authors then present the results of a statistical analysis carried out on three different test sites (Milan, Paris and Los Angeles). More than 170 ERS acquisitions have been processed to get an estimation of the PS density as a function of phase noise. Results show that, in urban areas, about 100 PS/km/sup 2/ can be identified and exploited for terrain deformation monitoring with millimetric accuracy.

Burst-mode SARs for wide-swath surveys

A spaceborne synthetic aperture radar (SAR) aimed at global monitoring with a short revisit time (12 days) is proposed. Such a system is not feasible in a conventional Stripmap mode because of the known relation between range coverage and azimuth antenna length, but it can be achieved in burst-mode SARs, like ScanSAR and TOPSAR. We detail the design of ScanSAR and TOPSAR sensors, provide a scheme to optimize the burst length in TOPSAR, and discuss an innovative burst-mode scheme defined as TOPSPOT. 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.

Flexible Dynamic Block Adaptive Quantization for Sentinel-1 SAR Missions

The letter introduces a novel quantizer suited for medium to high-resolution synthetic aperture radar (SAR) systems, like the forthcoming SENTINEL-1 SAR. The Flexible Dynamic Block Adaptive Quantization (FDBAQ) extends the concept of the Block Adaptive Quantization (BAQ), used in spaceborne SAR since the Magellan mission, by adaptively tuning the quantizer rate according to the local signal-to-noise-ratio (SNR). A design is presented aiming to optimize the average bit-rate, while constraining the minimum SNR. FDBAQ optimized performance is then evaluated using backscatter maps derived from ENVIronment SATellite (ENVISAT) data.

An efficient method for the azimuth compression of geosynchronous SAR data through sub-apertures processing

We propose an efficient method for the azimuth compression and Atmospheric Phase Screen estimation of Geosynchronous SAR data. The method is based on the iterative processing of sub-apertures of increasing size, allowing to gradually refine the quality of the focused data and of the estimated APS. The whole processing can be easily parallelized. Results over simulated data are shown.