Franck Daout

An Omega-K algorithm for SAR bistatic systems

Bistatic SAR uses separate flying transmitter and receiver platforms. There are two principal configurations : spatial invariant case, in which velocity vectors are equal; and spatial variant case, in which velocity vectors are not equal. ONERA and DLR performed experimental flights on the spatial invariant case in february 2003 [1]. The experiment was conducted using the X-band front ends that are compatible in terms of frequency (on a 100 MHz-Wide band). Estimation and compensation of the phase drift between the transmitter and the receiver master oscillator was presented in [1]. Until now, data have been processed with a back projection algorithm. This article investigates an Omega-K algorithm - or Range Migration Algorithm - for bistatic SAR systems in spatial invariant cases. First results of this algorithm on real data are included.

Multistatic and Multiple Frequency Imaging Resolution Analysis-Application to GPS-Based Multistatic Radar

This paper focuses on the computation of the generalized ambiguity function (GAF) of a multiple antennas multiple frequencies radar system (MAMF). This study provides some insights into the definition of resolution parameters of a MAMF radar system. It turns out that the range and azimuth resolutions are not the most suitable criteria to specify the MAMF radar resolution. Therefore a new set of resolution parameters is introduced like the resolution ellipse which expresses the resolution anywhere in the image plane or δ→max, (δ→min) which expresses the highest (lowest) bound of the spatial radar resolution. To point out the pertinence of our study, we illustrate it with a MAMF radar system built around GPS satellites. The effect of the radar system geometry on resolution is investigated. For several scenarios, the GAF and its numerical form, the point spread function (PSF), are computed and their results are compared.

Narrowband multistatic ISAR imagery system

This article deals with the imagery of mobile targets by using a multistatic radar (several transmitters and one receiver). First, we develop an original multistatic algorithm based on spatio-temporal SAR methods. As the transmitted signal is narrowband and the central frequency is weak, the final resolutions of the image depend on two parameters: the number of transmitters and the synthetic array length. The ambiguity function of the multistatic system is used to study the influence of these both parameters. We check this algorithm on realistic targets. Obtained images are interesting and allow first classification results. Thanks to numerical models of targets, we also show the importance of the transmitters locations as well as the need of a second receiver.

Fusion of multistatic synthetic aperture radar data to obtain a superresolution image

When using a single emitter and a single receiver, the Synthetic Aperture Radar (SAR) data gives information in the Fourier domain of the scene over a line segment whose width is related to the bandwidth of the emitted signal. The mathematical problem of image reconstruction in SAR then becomes a Fourier Synthesis (FS) inverse problem. When there are more than one emitter or receiver looking at the same scene, the problem becomes fusion and inversion. In this paper we report a Bayesian joint data fusion and inversion method to obtain a super resolution image. The proposed method shows a good performance on real data obtained at ONERA in France.

Fusion and inversion of SAR data to obtain a superresolution image

The Synthetic Aperture Radar (SAR) data obtained from a single emitter and a single receiver gives information in the Fourier domain of the scene over a line segment whose width is related to the bandwidth of the emitted signal. The mathematical problem of image reconstruction in SAR then becomes a Fourier Synthesis (FS) inverse problem. When there are more than one emitter and/or receiver looking the same scene, the problem becomes fusion and inversion. In this paper we report on a Bayesian inversion framework to obtain a Super Resolution (SR) image doing jointly data fusion and inversion. We applied the proposed method on some synthetic data to compare its performances to other classical methods and on experimental data obtained at ONERA.

Computation of bistatic RCS with NEC2 in a context of passive ISAR system

The modelling of electromagnetic scattering from two neighboring targets is investigated using an integral formulation solved by the well-know NEC2 code. To save the computational resource, we extract the impedance matrix which is a good describer of targets. From the scattered field, the bistatic Radar Cross Section (RCS) is computed. The convergence of the method versus the size of the wire-grid is investigated. Comparisons between two neighboring targets are studied. We show that the cross-polarization terms are more suitable to extract discriminators.

A multistatic synthetic aperture sonar to detect a cylinder lying on a rough interface: experimental results

Monostatic Synthetic Aperture Sonar (SAS) are high resolution systems for target imaging which are now of common use in the underwater acoustics domain. The objective of this work was to analyse what kind of information should be obtained from a multistatic SAS system. This idea has been applied in radar but very few works exist in the underwater acoustics domain. The applications could be detection and identification of buried mines or mines lying on the seabed and divers detection for harbour protection. These applications deal with the problem of target detection and identification near a rough surface. To show what can be obtained with a multistatic SAS processing, we have performed an experiment with a circular cylinder of 1 cm diameter lying on a rough interface made of sand grains of 1 mm diameter. Measurements were performed in a tank with both a multistatic and a monostatic SAS systems. The signal used to insonified the target area was a short impulse with a 2 MHz central frequency which correspo...

Wave scattering in underwater acoustics

In underwater acoustics it is necessary to take into account the wave scattering by the seafloor. For example, on sonar pictures the speckle noise proceeds from the constructive and destructive interferences between al‐lthe waves reflected by the elementary scatterers. The origins of this phenomenon are seafloor roughness and its acoustic properties, wave incidence, frequency, multiples reflections, the dimensions of the insonified surface, etc. The aim of this study is to characterize the scattering of waves exclusively from the roughness. Thus a hypothesis of perfectly reflecting surface is taken. Moreover, specific‐geometry periodic surfaces are considered to take into account the multiple reflections and the shadow area easily. Finally it is supposed that the roughness and the wavelength are of the same size. The models to describe the scattered field are based on Kirchhoff’s theory and on Fraunhoffer’s diffraction theory. Some experiences in the acoustic tank yield good agreement between theoretical ...

Bistatic scattering: A new way to improve sonar detection capabilities?

In the field of seabed sonar imagery, it is necessary to establish local scattering models to improve the performances of the detection or recognition algorithms. In this paper, we present the Probability Density Function (PDF) of the acoustic intensity scattered by a natural profile as a function of the bistatic angle. To do this we have developed a 1‐D bistatic scattering model called NEWS (Numerical Estimation for Waves Scattering) that incorporates physical phenomenons like multiple reflections, shadow and the reflection coefficient of the profile. Moreover, NEWS takes into account acquisition parameters like sensors characteristics and their positions in relation to the center of the illuminated area. Gaussian spectra for the profile height fluctuation are considered. Five hundred profiles are generated. For each profile NEWS’s algorithm gives the angular distribution of the scattered field in amplitude and in phase for all geometries and as a function of incident and scattered wave. The acoustic int...