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International audience; For foliage penetrating (FoPen) radar development, we previously developed a hybrid volume-surface model, named Domain dEcomposition Model (DEMOS), to evaluate the electromagnetic scattering from large scenes composed by targets (metallic objects) placed in a natural environment (dielectric object). In this letter, we compare the scattered field obtained by DEMOS with the quasi-monostatic measurements done in an anechoic chamber on scaled models composed of dielectric and metallic structures. For all measurements, we consider both polarizations, HH and VV. Our final objective is to determine the optimal configurations for the detection of a target placed in a forest environment in the very high-frequency (VHF)-UHF frequency bands.

International audience; This paper presents fully polarimetric bistatic radar scattering measurements on groups of dielectric vertical and/or tilted square cross-sectional cylinders above a conductive circular plate in the frequency range of 6-18 GHz. The experiments have been conducted in the BABI facility at the French Aerospace Lab (ONERA). The imaging experiments consider an azimuthal bistatic radar configuration with a single incident direction and many scattering directions, in the way that the receiver positions synthesize a 1-D circular aperture in a horizontal plane around the focal point of the anechoic chamber. The bistatic scattering by the different sets of cylinders is also achieved through numerical simulations by using a volume-electric-field-integral-equation model employing a method of moments. First, theoretical and experimental bistatic radar-cross-section values are confronted. The comparisons show a good agreement for all polarization cases ($vv$ , $hv$, $vh$, and $hh$). Then, a near-field reconstruction algorithm has been extended from a monostatic to our bistatic radar configuration in order to generate the reflectivity maps by focusing both theoretical and experimental scattered fields. The comparisons of the 2-D bistatic synthetic aperture radar images show that the two prediction techniques are accurate.

The Message Passing Interface implementation ensures a reduction of the computing time and a distribution of the necessary memory to each processor. The 3D full-wave model for electromagnetic scattering from forest environment, based on the volumetric integral Equation formulation of the electric field, combined with the Characteristic Basis Function Method (CBFM) and implemented in Message Passing Interface (MPI) parallelization is described in this paper. This combination of the CBFM and the Method of Moments (MoM) allows us to reduce significantly the size of the initial electromagnetic scattering problem.

International audience; In this paper, a coherent forest scattering model based on the electric-field integral representation is developed. This model gives the scattered field by the forest, resulting from the interaction of an electromagnetic plane wave with its main elements (trunks, branches, and plane ground) in a frequency range of 100 to 400 MHz. The Method of Moments is used to solve the electric-field integral equation. In our treatment, there are three possible scattering mechanisms that contribute to the scattered field defined as follows: 1) single-; 2) double-; and 3) triple-bounce scattering mechanisms. The internal fields inside the tree trunks and branches are calculated by considering all of the multiple-scattering interactions within the forest. Our model is then constructed by coherently summing the three scattering mechanisms previously given. We can also obtain an approximate result by ignoring some or all of the multiple-scattering interactions in the calculation of internal fields inside the trees. The aim of this paper is, first, to determine the relative contribution of each scattering mechanism to the total scattered field, followed by the relative contribution of tree-trunk and branch scattering responses to the total scattering field, and, finally, the multiple-scattering interaction effects on the total backscattered field.

International audience; In remote sensing for forest monitoring, Synthetic Aperture Radar (SAR) imaging is a powerful tool to investigate wide forested areas, particularly at low frequencies (less than 1GHz) where the electromagnetic waves penetrate deeply under the forest canopy. Radar measurements allow us to obtain information on the forest biomass, such as density, heights and dielectric properties of trees. In order to extract this information, it is necessary to analyze the wave-tree interactions involved when SAR measurements are performed. At low frequencies, the small branches and leaves of trees do not significantly contribute to the electromagnetic fields scattered by a forest area and can be safely neglected. The main contributions to the scattered field come from the trunks and primary branches. In this context, we have built up an approximate model where the latter are considered as finite circular cylinders. The total scattered field is then obtained by coherently adding the contributions of the different trunks and branches and the contribution of each of them is obtained through the coherent sum of various elementary scattering mechanisms such as single, double and triple bounces.

Herein, we suggest a fast approximate 3D numerical model for the interaction of an electromagnetic wave with a forest. Contrarily to other such approximate models found in the literature, this model accounts for the reciprocity of the double bounce scattering mechanism observed in particular configurations. This reciprocity is enforced at the scattering matrix level. The model is tested and compared to a rigorous model based upon an integral representation of the fields.

International audience; In this paper, we present numerical simulations and indoor bistatic scattering measurements on scaled targets. The targets are vertical and/or tilted dielectric parallelepipeds representing the main forest elements (tree-trunks and primary branches) at VHF and low-UHF frequencies. They are placed above an aluminum circular plate to simulate a flat ground. The measurements have been conducted in the anechoic chamber of the ''Centre Commun de Ressources Micro-ondes'' (CCRM) in Marseille, France. A 3D forest scattering model using a Method of Moments (MoM) is deployed to simulate the electric fields scattered by these targets. Two radar geometric, azimuthal and zenithal, bistatic configurations with special attention to the specular direction have been considered. Simulation results and experimental data are confronted for both {VV-} and {HH-}polarizations in order to evaluate the accuracy of our model. We have obtained a very good agreement between theoretical and experimental scattered fields for both the magnitude and phase.

A 3D coherent scattering model simulating the interaction of electromagnetic waves with forests has been developed. It is obtained by means of a full wave approach, based on an integral representation of the electric field. A method of moments is used to solve the integral equation and compute the scattered fields related to the various scattering mechanisms as well as the contribution of tree-trunks and branches. This model is used here to evaluate the impact of electromagnetic coupling effects between a group of scatterers (which can be the branches and the trunk of a single tree, multiple tree-trunks, or multiple trees) for monostatic and/or bistatic radar configurations. To validate our model, we compare our simulation results with anechoic chamber measurements.

In this paper, an electromagnetic scattering model based on the electric field integral representation is used to separate the scattering mechanisms involved in the interaction of an electromagnetic field with forested areas. This model is used to examine the different coupling effects between the main scatterers (trunks and branches) and those between the scatterers and the ground.

International audience; The interpretation of radar data would ideally require extensive and numerous observations. However, the number of observations is limited by the difficulty and the cost of acquiring ground truth and radar data. On the other hand, numerical models can provide a wide range of situations, both in inputs and in outputs. More precisely, they have to provide radiometric, polarimetric, and interferometric simulations and be applicable to various forested areas (high density, high/low moisture, inhomogeneous area, etc.) and radar configurations (low/high frequency, bistatic observation, etc.). This paper is dedicated to the presentation of the capabilities of a descriptive coherent scattering model (COSMO) applied to the electromagnetic study of the backscattering by forested areas. Improvements have been implemented in order to produce in output a radar image, which can be treated with the same polarimetric and interferometric tools as those applied to real synthetic aperture radar images. Thus, comparisons are possible. COSMO has been widely tested from P- to L- bands, over temperate and tropical forests and applied to radiometry, polarimetry, and interferometry. It appears finally as an efficient simulating tool to carry out parametric studies and to analyze how the total scattered field is built from canonical mechanisms and individual scatterer contributions.