This paper concerns three dimensional imaging of volumetric natural environments, such as snow packs and sea ice, using a ground based SAR system and X and Ku bands. The ground-based acquisition ...system consists of a vector network analyzer and an multi-static antenna system, moved along two orthogonal directions, so as to obtain a two dimensional synthetic array. Tomographic processing techniques, based on the coherent combination of the acquired SAR signals and adapted to the three-dimensional focusing of very high resolution data, are proposed. Specific automatic correction approaches, aiming to compensate for acquisition errors and uncertainties, are developed in order to improve the quality and descriptiveness of the tomograms. It is then shown that three dimensional imaging permits to retrieve the vertical structure of shallow volumetric media at a resolution of few centimeters and to emphasize physical scattering phenomena that cannot be observed from classical two-dimensional SAR data sets.
The objective of this paper is to provide a better understanding of the impact of temporal decorrelation on the tomography phase of the P-band Synthetic Aperture Radar (SAR) BIOMASS mission, 7-th ...Earth Explorer of the European Space Agency. In this context, in the framework of the Phase A studies of the BIOMASS mission, the airborne TropiSAR 2009 and ground-based TropiScat 2011 experiments were conducted over the site of the tropical forest Paracou, French Guiana. The P-band SAR tomographic data acquired during TropiSAR campaign allowed us to reconstruct 3-D high resolution data, whereas TropiScat experiment provided vertical temporal coherence of the vegetation. These data therefore allow us to generate a BIOMASS P-band SAR data stack that accounts for both the 6 MHz bandwidth limit and temporal decorrelation. To do this, we developed a tomo-graphic simulator, which can combine 3-D high resolution data from TropiSAR and the temporal decorrelation from TropiScat data-sets, to provide the most realistic temporal BIOMASS tomographic data. The resulting tomograms and forest heights were observed to change acceptably as long as the revisit time is 4 days or less. Therefore, the revisit time for the BIOMASS tomographic phase at 3-4 days as proposed should be feasible.
The objective of this paper is to provide a better understanding of tomographic capabilities in characterization of dense forested areas at P-and L-band. The analysis is carried out on airborne data ...acquired by ONERA over the site of Paracou, French Guyana, during the ESA campaign TropiSAR. The results shown support the idea that ground- and -volume interactions play a negligible role at L-band, whereas they are significant at P-band. For a dense forest of 30 m and more, there is very weak ground contribution at L-band. The L-band tomographic profile is quite disturbed as compared to the P-band profile in dense tropical forest areas. In this condition, the use of tomographic imaging at L-band in tropical forests appears limited. However, when the forest top height is roughly below 20 m (e.g., in forest regrowth), the tomographic results are expected to be the same as in boreal forests. Whereas P-band tomography allow us to retrieve the whole forest vertical structure, better characterizing of the ground and/or volume scatterings and providing an unique solution in high biomasss ranging from 150-600 t/ha.
This paper investigates the ability of Polarimetric SAR Tomography (PolTomSAR), performed at P-band, to retrieve Above-Ground-Biomass (AGB) over dense tropical forests. PolTomSAR techniques allow an ...accurate estimation of the backscattered power distribution in the vertical direction. A first tomographic biomass estimator, relating AGB to the backscattered power in the higher part of the vegetation is analyzed through a Random-Volume-over-Ground (RVoG) analytical description of a forest profile. A PolTom-RVoG derivation of the power backscattered by the upper vegetation layer is performed as an integration of the reflectivity along the volume vertical structure. This integration is carried out over a domain fixed by TomSAR resolution and tree height, leading to a novel and accurate ABG estimator. The proposed techniques are applied to P-Band data acquired over the Paracou data site on French Guiana in 2009, in the frame of the European Space Agency (ESA) TropiSAR campaign.
This paper aims at characterizing the scattering mechanisms occurring at the ground level in a tropical forest illuminated by a P-Band SAR. The analyzed data set is the one collected by ONERA over ...Paracou, French Guyana, in the frame of the ESA campaign TropiSAR. The favorable baseline distribution of this data set results in the possibility to remove most contributions from the vegetation layer by tomographic techniques, thus allowing a direct investigation of ground scattering. Two major conclusions are drawn: i) double bounce scattering from trunk-ground interactions is observed to be the dominant scattering mechanism at the ground level on flat terrains, whereas it rapidly tend to vanish as the topographic slope increases; ii) the characteristic parameter that rules trunk-ground scattering is not the tree height, but rather the available free path facing the tree, as a result of the presence of nearby trees or understory preventing double bounce scattering from taking place whenever the ground bounce occurs too far away from the considered tree.
The next ESA Earth Explorer Core Mission BIOMASS is envisaged to collect multiple baselines on selected areas during the initial phase of its lifetime. Such data will allow to image the vertical ...structure of the vegetation layer to within a vertical resolution of about 20 m, sufficient to decompose the backscattered power from a tropical forest into two-three layers. The information provided by tomography has recently been shown to be strictly linked to above ground biomass (AGB) in tropical forest, therefore providing a valuable tool for ABG estimation. The aim of this paper is to present a bird-eye overview of BIOMASS Tomography, along with the main experimental results from airborne campaigns flown during Phase-A BIOMASS activities.
In this paper we discuss some relevant features observed concerning wave penetration at P-band in boreal and tropical forests. The discussion will be based on results obtained from the ...multi-polarimetric and multi-baseline data-sets relative to the forest sites within the Krycklan river catchment, Sweden, and the area of Paracou in French Guyana, collected in the frame of the ESA campaign BioSAR 2008 and TropiSAR 2009, respectively. The analysis is carried out by exploiting the SAR tomography technique, which allows to separate backscattering contributions from different heights within the vegetation layer. One first relevant result is relative to the difference between the vertical distribution of the backscattered power in the two investigated test sites. In the boreal forest site the most relevant scattering contributions are observed at the ground level, not only in copolarized channels but also in HV, whereas in the tropical forest the presence of scattering from the ground is poorer and the vegetation volume is well visible. Most relevant features of the investigated tropical forest site are those relative to the dependency of the vertical backscattering distribution with respect to topographic slope and forest biomass. In particular, the innermost forest layer is observed to be substantially invariant to topographic slopes, whereas the backscattered power at 30 m above the ground is observed to yield the best connection with forest biomass, resulting, in this case, in a correlation factor of 0.82 with respect to in-situ measurements at 125 m spatial resolution.
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.
The paper discusses methods for radiometric calibration of repeat-pass interferometric SAR stacks based on Persistent Scatterers. Coherent and non-coherent approaches for the estimation of the ...radiometric gain are compared. Furthermore, an estimator of the beam pointing in elevation in proposed. Evaluation of performances is carried out basing on both simulated and COSMO-SKYMED data.
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