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Several popular metallic bistatic calibration objects are investigated, including a sphere, long and short cylinders, dihedral, trihedral, circular disk and wire mesh. Comparisons are made between the advantages and disadvantages of various objects for calibration. The analysis addresses sensitivity to object alignment error, availability of accurate radar cross section (RCS) calculations and bistatic RCS levels. Both theoretical concepts and practical considerations are discussed based on measurements accomplished at the European Microwave Signature Laboratory (EMSL) of the EC Joint Research Center (JRC) in Ispra, Italy. This facility has the capability to produce far-field fully polarimetric precision bistatic measurements in a 30 cm diameter quiet zone, suitable for comparing different calibration objects. Index Terms--Bistatic, calibration, radar cross section (RCS), scattering.

Several popular bistatic calibration techniques are investigated and comparisons made between the relative merits of the various techniques. The analysis addresses sensitivity to object alignment error, sensitivity to polarization impurity, and ease of implementation. Both theoretical concepts and practical considerations are discussed based on measurements accomplished at the European Microwave Signature Laboratory of the European Commission Joint Research Center, Ispra, Italy. This facility has the capability to produce far-field fully polarimetric precision bistatic measurements in a 30-cm-diameter quiet zone, suitable for comparing different calibration methods. Index Terms--Bistatic, calibration, measurement, radar.

In this paper, the circular polarization coherence, [rho]RRLL, is investigated as a potential estimator of terrain surface roughness and small-scale slopes. The studies utilize microwave backscatter collected from 1) dielectric surfaces in an anechoic chamber and 2) a desert test site using P-, L-, and C-band NASA/JPL AIRSAR data. These experimental studies and supporting theory, indicate a sensitive decrease of |[rho]RRLL| with increasing surface roughness ks over a range 0 [less than or equal to] ks [less than or equal to] 1. For the present studies this decrease is caused largely by the depolarizing effects of small-scale surface slopes in the azimuth direction rather than by volume, or multiple scatter. For cases when the scatter is reflection symmetric, the value of |[rho]RRLL| depends on the surface roughness and on the local incidence angle. The dependence of |[rho]RRLL| on the local incidence angle is supported by theory and experimental results. For these same scattering cases, however, |[rho]RRLL| is independent of the surface dielectric constant. Estimation of the functional dependency of |[rho]RRLL| versus ks, for a mid-range incidence angle, has been carried out using roughness estimates derived from an empirical model. Further studies, involving more incidence angles, are required to develop a complete model to invert the data. Additional results show that the Re[[rho]RRLL] is often preferable over |[rho]RRLL| as a roughness estimator when scatter occurs from vegetated areas. A comparison between Re[[rho]RRLL] and a related polarimetric parameter, the anisotropy A, indicates that for scatter having k8 [less than or equal to] 0.5, Re[[rho]RRLL] is a more sensitive estimator of surface roughness. Index Terms--Radar polarimetry, slopes, surface roughness, synthetic aperature radar (SAR).

The objective of this study is to develop a surface scattering model including multiple scattering based on extending an existing integral-equation-based surface scattering model (IEM). This is done by removing a simplifying assumption in the spectral representation of the Green's function used in the scattered field expression of the IEM surface scattering model. It is noted that while this simplifying assumption is valid and useful in single scattering calculation, it is a hindrance to separating and identifying terms responsible for surface multiple scattering. Furthermore, it is demonstrated that the removal of this assumption permits multiple surface scattering calculations to be carried out and shown to agree with controlled laboratory measurements acquired from known surfaces.

A comparison between indoor scatterometric and SAR measurements of distributed targets is presented. In particular, the backscattered signal statistics (in amplitude and phase) obtained in these two types of measurements are compared for different surface parameters (roughness and correlation length) and varying spatial resolutions in the SAR images. Experimental data have been taken in the European Microwave Signature Laboratory (EMSL) at JRC, an indoor facility which is able to measure extended targets both in scatterometric and linear SAR mode under the same conditions. The results confirm that, with spatial resolutions in the SAR image smaller than two autocorrelation lengths (ACL), the statistics of the backscattered signal depends significantly on the resolution cell size. For larger resolution cells, the experimental data are consistent with the Rayleigh model. This experimental finding substantially confirms the results based on numerical simulations, previously presented in the literature.

In this paper, we present the experimental test of a SAR system that uses a fixed ground-based receiver and, as an illuminator, a TV broadcasting satellite. The synthetic aperture is obtained by exploiting the small daily motion of the satellite. The spatial resolution and the link budget are also analyzed. Index Terms--Radar imaging, satellite broadcasting, synthetic aperture radar (SAR).

This work focuses on the bistatic scattering nature of complex metal objects and assesses the accuracy of several common bistatic scattering prediction techniques: a common physical optics/physical theory of diffraction (PO/PTD) based simulation package, Kell's scattering center-derived mono-static-to-bistatic equivalence theorem (MBET), and Crispin's PO-based MBET. Monostatic and bistatic measured and simulated data are gathered and compared for three test objects of increasing complexity. Delineation between specular and nonspecular effects is highlighted to help explain when prediction techniques fail. The PO code proves erroneous at low grazing angle receive antenna positions and does not predict nonspecular type scattering well. Interestingly, however, it does accurately compute specular reflections from electrically small surface features. Kell's and Crispin's MBET's are also studied. For simple objects (e.g., flat plate) both MBET's predict scattering fairly well for bistatic angles of 30--40 [degrees], with Kell's having a slight edge at larger angles. As the complexity of the object increases, MBET accuracy decreases. Neither MBET is particularly capable at bistatic angles greater than 15 [degrees] for objects whose scattered field is primarily comprised of specular interactions (minimally complex). Both tend to predict lower returns at larger bistatic angles. MBET accuracy holds for smaller bistatic angles with increasing geometrical complexity. The object whose geometry contains large shadowing features and a cavity supports multi-bounce, diffraction, and surface wave phenomena. The accuracy of both MBET's is limited to bistatic angles of only 5--10 [degrees] in this case. Each tends to predict higher than measured scattering at larger bistatic angles. Index Terms--Bistatic, equivalence theorems, radar cross section.

Multifrequency polarimetric scattering and emissivity measurements have been carried out on three experimental dielectric models, characterized by random surfaces with different statistics. The results of the measurements have been compared with simulations obtained through physical models based on the classical approximations of physical optics (PO), geometrical optics (GO), small perturbation (SP),and integral equation model (IEM). The comparison of experimental data with theory has shown that, even when the parameters of the observed surface are well determined and known, some discrepancy may exist between models and measurements. Except for a few cases, this discrepancy is quite small and may be insignificant for many practical applications, The IEM has been proven to have a wider range of applicability with respect to other tested approximations. Index Terms--Electrmagnetic modeling, microwaves, surface scattering.

Presents a comparison between indoor scatterometric and synthetic aperture radar measurements of distributed targets. Data focusing; Near-field condition; Targets characteristics and measurement parameters; Polarization of rough surfaces with incidence angles.