Elise Colin-Koeniguer

Investigating Attenuation, Scattering Phase Center, and Total Height Using Simulated Interferometric SAR Images of Forested Areas

The objective of this paper is to examine the link between the attenuation coefficients and the interferometric phase center heights, for several frequencies from P- to L-band, and to study the extent to which it depends on the canopy architecture and description. This paper relies on the use of a coherent and full polarimetric scattering model, which simulates the fields backscattered by a forested area. In the first part, we study the behavior with a frequency of the interferometric phase center heights, and in the second part, we focus on the attenuation coefficients. Then, we compare the behaviors of these two quantities, and we propose to empirically derive a relation between these two quantities and the mean forest height. Finally, we investigate if a change in the initial forest or radar configuration has an impact on the determination of this relation.

Influence of Geometrical Configurations and Polarization Basis Definitions on the Analysis of Bistatic Polarimetric Measurements

Within the frame of bistatic polarimetry, this paper discusses the entangled effects of bistatic geometry and target features on polarimetric measurements. Three different geometrical effects are distinguished: antenna rotations, target orientation, and bistatic angle. Antenna rotations are addressed through the use of polarimetric bases taking the scattering plane as the reference plane. Target orientation effects are not considered since only spheres are studied. This paper focuses on the bistatic angle effect through a bistatic polarimetric analysis on classical parameters. Targets consisting of single or multiple spheres in the resonance region are investigated. Finally, the results of indoor polarimetric measurements on such targets are presented and discussed.

Bistatic scattering from forest components. Part II: first validation of a bistatic polarimetric forest model in the VHF-UHF band [225–475 MHz] using indoor measurements

This paper introduces the validation of the extension of a scattering model of forests to the bistatic configuration (COBISMO). The measurement in an anechoic chamber is first described. The various stages of the validation process are presented. One dielectric cylinder on a metallic plate is chosen as the canonical element to be tested. Indoor measurements are confronted with the results predicted by the model, first in the horizontal/azimuthal plane, then in the vertical/elevation plane. Then mutual coupling is also investigated using a group of three cylinders. The agreement between simulation and measurement is surprisingly good in light of the precision of such indoor measurements. Several other aspects are discussed: the influence of the frequency, of the shape of the section of the cylinder, and polarimetric effects.

Bistatic scattering from forest components. Part I: coherent polarimetric modelling and analysis of simulated results

This article deals with the study of bistatic scattering by forested areas using a coherent scattering model. The contribution of the scatterers is considered (trunks, branches), as well as their interaction with the ground. This code has been extended from monostatic to bistatic configurations and we present all the tests we have performed with this tool in order to validate it as far as possible. The transmitter is at a fixed location and the receiver moves either in the incidence plane (only θ s varies) or in all positions (θ s and φ s both vary). Our objective is to determine the main trends characterizing bistatic scattering by a forest. We study the variation of the scattering coefficient, when evolving from the backscattering to the specular configuration (only θ s varies). Both radiometric and polarimetric aspects are analysed, first when considering a simple forest of trunks and then a forest with trunks and branches. Finally, we analyse the impact of both θ s and φ s for two cases: a vertical dielectric cylinder in free space and a set of vertical dielectric cylinders, arranged in different ways. Here again, the radiometric and polarimetric aspects are investigated to check the electromagnetic behaviour.

Determination of mechanisms that can occur in NLOS urban canyon

In this paper, we are interested in identifying all areas inside a urban canyon that can be illuminated by a radar in NLOS (non line of sight) configuration. We developed a simple model to identify, according to each canyon configuration, the ground canyon areas illuminated by the radar and also the non illuminated areas. We test the results of our algorithm for a specific canyon. To validate our theoretical results we finally present some measurements that will be performed in the anechoic chamber of ONERA on a scaled urban canyon in the case of far field.

A New Light on SAR Backscattering Coefficient and Interferometric Coherence in Layover Areas

This letter focuses on the analysis of layover effects in interferometric synthetic aperture radar (SAR) data of urban areas. In particular, we derive two formulations to express the backscattering coefficient and the interferometric coherence in this case. These equations show that the backscattering coefficient and the interferometric coherence in layover areas can be seen as a combination of the backscattering coefficients and interferometric coherences of the individual scattering mechanisms. These formulations are then tested on interferometric SAR (InSAR) data and analyzed statistically.

Analysis of a NLOS canyon in an InSAR image of a urban area at Ka-band

In this paper, our concern was to help understanding the different scatterers responses in an interferometric image of a urban area by studying the different mechanisms that can occur inside the urban canyon. This study relies on a geometric code we specifically developed for this kind of scene. In this example, because of the reflections on the walls, we highlight the impact of the Brewster angle on the interferometric signature. For this reason, we recommend the use of different polarization and incidence angles for urban areas analysis of InSAR image.

Analysing urban areas in the frame of non line of sight target detection. Electromagnetic modelling, validation and application to real data in Ka-band

We present in this communication our results on the study of urban canyons. This simple scene has been retained to produce a first analysis on urban areas, as the canyon can be seen as one canonical structure inside cities. Our initial goal was to determine if a stationary target can be detected within a canyon in a non-line of sight configuration. Our strategy was to develop simple but fast algorithms to study such configurations and to complete these codes with a commercial software in order to further analyze the absolute amplitude of the backscattered fields. These codes have been applied on real SAR and INSAR data acquired by ONERA over industrial areas at Ka-band.

Optical Scale Polarimetric Device for Nanotube Forest Measurement: An Opportunity to Anticipate Bistatic Polarimetric SAR Images of Tree Trunk Forests at P-Band

This paper investigates a new polarimetric device that produces reduced scale measurements for bistatic radar. The optical scale device is proposed to overcome the lack of real bistatic and full polarimetric radar acquisitions for forest of trunks. It is based on the scale invariant rule that is deduced from the Maxwell equations. From this principle, the electromagnetic (EM) response is kept at the reduced scale if the illumination wavelength is scaled and if the permittivity remains the same. This last condition needs the use of a carefully chosen material at optical scale. Nanoscale scenes are composed of carbon nanotubes (CNTs). They present several advantages: their arrangement is similar to the structure of a forest of trunks, their shape, and density can be controlled, it is possible to create very large scenes composed of thousands of elements, and finally their permittivity at optical wavelength is about the same order of magnitude than the permittivity of the tree trunks at radar wavelength. They are measured under the view of a microscope objective with a 633-nm wavelength laser playing the role of the EM source. The device images at once the forest polarimetric response, for a given transmitter location, and for the entire set of angular positions of reception. Two samples of forests with different densities are measured. They are analyzed using the Cloude and Pottier decomposition and the Lu and Chipman decomposition. The produced results are unprecedented on forest-like environment and it would be very helpful for the radar community.

Understanding and validation of the polarimetric scattering of a forest for bistatic P-band SAR measurements

The objective of this paper is to propose an alternative measurement device at optical scale to help understanding of bistatic polarimetric SAR images of forests. The device is employed to measure nanoscale trunk forests with a 106 scale factor. Considering the scale invariant rule in electromagnetic scattering this device would enable to predict the Mueller matrix of a whole tree forest for P band radar measurements. The device presents the advantages to be low cost and to get a complete set of bistatic configurations at once. Moreover, the measurements are very fast and would potentially be done on infinitely diverse and well controlled forest structures. Multiplicative decompositions of the Mueller matrix are presented. We underline the trunk density influence for an entire scope of bistatic configuration.