This paper proposes an algorithm for estimating the fractal dimension of real sea bistatic synthetic aperture radar data. The algorithm is based on the use of the fractal dimension estimated by the box counting method to detect the sub-data which contain the targets. Based on this approach, the performance of the fractal detector proposed in this paper was demonstrated by the evaluation of the probability of detection by means of Monte Carlo simulation and was verified that we can use the fractal dimension to distinguish between targets and clutter, even for a small signal-to-noise ratio.

This paper examined the feasibility of performing bistatic Radar Cross Section (RCS) measurements in the Boris Vian anechoic chamber. To test this anechoic chamber, a small PEC circular cylinder is selected as a target. The capability to measure the bistatic RCS of a target versus frequency and versus target azimuth angle is established. Accurate bistatic RCS measurements are obtained using a Vector Network Analyzer and using background subtraction, bistatic calibration, and software range gating. A method to establish the chamber directivity is proposed. The accuracy of the measurement is estimated and a new value of the RCS sensibility is given as a function of the value of the chamber directivity.

The ultimate simplified point scatterer model contains no object's geometry informations, so a more complex prediction model containing geometrical informations is needed. The Physical Optics (PO) approximation has been widely used and considered as a good approximation of the far field electromagnetic scattering. Here, a forward model of bistatic scattering by PEC infinite elliptic cylinder based on the Physical Optics approximation is presented. The aim is to develope a simple scattering model for 2D targets illuminated by a monochromatic wave bistatic Radar. The reduced model is obtained by applying the stationary phase method to the PO integrals in both TE and TM wave cases. A parameter estimation procedure is also presented in order to examinate the efficiency of the presented model.

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.

A forward model of bistatic scattering by PEC infinite elliptic cylinder based on the Physical Optics (PO) approximation is presented. The model is obtained by applying the stationary phase method to the PO integrals in both TE and TM wave cases. The aim is to obtain the shape and size of 2D targets illuminated by a monochromatic wave bistatic Radar. A parameter estimation procedure based on the forward model is presented. Synthetic data are used to show the efficiency of the proposed method and the noise effect is also investigated.

This paper deals with the imaging of a moving target using a multifrequency and multistatic radar consisting in one receiver and several narrowband transmitters. Considering two hypotheses about the studied target, we derive two multistatic inverse synthetic aperture radar processors: the first one, which models the target as a set of isotropic points, performs a coherent sum of bistatic images; the second one, which models the target as a set of nonisotropic points, performs an incoherent sum of bistatic images. Numerical simulations are done, which demonstrate the efficiency of the second processor. We also apply both processors to a multistatic passive radar scenario for which the transmitters are FM stations located in a realistic configuration. We study the system performance in terms of resolution and sidelobe levels as a function of the number of transmitters and of the integration time. Both processors are applied to similar complex targets for which the scattered fields are simulated by a numerical electromagnetic code. The resulting multistatic radar images show interesting characteristics that might be used by classification algorithms in future work.

In this study, comparisons are made between two imaging techniques in the context of the Multistatic Synthetic Aperture Sonar (SAS): the Matched Filtering method and a reconstruction method based on the Kirchhoff Approximation (KA). The Matched Filtering Algorithm (MFA) is the classical method used for image formation purposes in synthetic aperture systems. In this method the field diffracted by the target is approached by the "point scatterers" model. One of the first objective of this work is to develop a more complex and more realistic model than the well known "point scatterers" model. In addition, the aim is to get not only the shape and the size of target but also some quantitative information about its physical properties. Thus, a forward model based on the KA is proposed to get a more realistic description of the scattered field and a reconstruction method has been obtained through the use of a 2-D Fourier transform of this forward model. The algorithm hence obtained is named: "Imaging Reconstruction Algorithm in the Kirchhoff Approximation" (IRAKA). In this paper the IRAKA is compared to the MFA in order to check its capability to reconstruct target shape.Images of 2-D targets of circular and elliptic cross-sections are reconstructed with the MFA and with the IRAKA from both numerical data and tank experimental data. These imaging methods are compared in terms of quality of the shape reconstruction and in terms of their robustness to noise in a given multistatic configuration. Both algorithms are also used to reconstruct images of a 2-D target of circular cross-section in a multistatic forward looking SAS context. With a good Signal to Noise Ratio (SNR) we get better results with the IRAKA than with the MFA in terms of the quality of target shape reconstruction. In presence of additive white Gaussian circular noise, the MFA off course, gives better results than the IRAKA. Nevertheless, using a technique of stabilization of the deconvolution, it has been possible to improve the performances of the IRAKA even in presence of additive noise.

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 corresponds to a ka about 40. Images of the cylinder in presence of clutter have been reconstructed with the matched filtering algorithm from monostatic and multistatic acquisitions and have been compared.

This paper presents research results in space-surface multistatic synthetic aperture radar (SS-MSAR) with non cooperative GPS satellites. The goal of this paper is to characterize such a system in an ISAR context, with a moving ground target.point spread function (PSF) are defined and used in this work to estimate the performance in term of resolution. These criteria are computed, and compared, for several scenarios with targets of different velocities.

This paper presents research results in space-surface multistatic synthetic aperture radar (SS-MSAR) with non-cooperative GPS satellites. The effect of the system's geometry is investigated. We will show that in SS-MSAR, the spatial resolution depends on the geometry of the system, i.e. satellite-receiver-target positions relative to each other. General ambiguity function (GAF) and the point spread function (PSF) are defined in our case in a 3D case corresponding to our study. These criteria are then computed, and compared, for several scenarios including one (bistatic case) to three emitters (multistatic case).

The modelling of electromagnetic scattering from two neighboring-targets is investioated 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.

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.

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 Synthetic Aperture Radar (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.

The bistatic scattering from a rough surface is simulated by a computer program for a wide angles range. The effect of shadowing and multiple scattering are taken into account. To describe the scattered field the Kirchhoff theory is used. The probability density functions (pdf) of normalized scattering pressure (modulus) are compared with the Weibull, lognormal and K-distribution pdf. The phase distribution are also studied. The values of the distribution parameters estimated using maximum likelihood (ML) estimators are obtained. The Kolmogorov-Smirnov goodness of fit test is used to determine which of the distribution fits the data better. It is observed that the effect of the size of the illuminated area is important on the phase distribution

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 intensity is then treated as a random variable, and histograms are established. The PDF of the scattered intensity is compared to the K, Weibull and lognormal distributions and we examine the statistical informations providing by bistatic sonar.

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 and experimental results. They show that the orientation and the area of the insonified and observed surfaces are parameters for the scattering angles and for the relative scattered amplitudes.

The bistatic scattering from a rough surface is simulated by a computer program for a wide angle range. The effect of shadowing and multiple scattering are taken into account. To describe the scattered field the Kirchhoff’s theory is used. The probability density function (pdf) of the scattered intensity is compared with the Weibull, Lognormal and K distributions. The phase pressure is also studied. The values of the distribution parameters estimated using maximum likelihood estimator are obtained as a function of the bistatic angle. The KolmogorovSmirnov distance is used to determine which of the distribution fits the data better. It is observed that the exponential distribution is a good approximation for small incident angle. Nevertheless, it is shown that for grazing incidence and near the forwad direction, the Weibull’s pdf with a shape factor equal to 4 is more appropriate. The study of the intensity scattered in the forwad direction shows that its pdf deviates of the exponential’s distribution when shadowing and multiple scattering occur. It seems that for this special case, it is necessary to find a new clutter distribution like Weibull’s pdf.