| A new real beam interferometric processing technique, called Adaptive Clutter Erasure (ACE), is investigated for applicability to ground clutter suppression in airborne radar systems. By analysis and simulation, the viability of the ACE concept as a next generation clutter suppression technique is demonstrated to achieve performance enhancements commensurate with currently implemented techniques. Research results indicate the ACE concept provides a reliably consistent 10 dB Signal-to-Clutter Ratio (SCR) advantage over the APG-63, an operational radar system used for baseline comparison. ACE system concept development and performance predictions are conducted in conformity with the physical and operational design parameters of the APG-63, namely the operating frequency band, typical tracking scenarios, aperture size and polarization, element spacing and weighting, and field pattern response. Performance degradations for the limited number of scenarios where ACE provides minimal or no advantage, i.e., scenarios including platform roll or large target depression angles, are "as expected" in the sense that simulation results are consistent with theoretically established principles.; In support of ACE concept validation, a novel multi-layer 3-D clutter model is developed by incorporating existing clutter reflectivity statistics and measured terrain elevation data. This new 3-D clutter model offers tremendous flexibility by accurately characterizing the relative altitude, slope, type, surface thickness, probabilistic reflectivity, and shadowing of terrain on a pixel-by-pixel basis. This is in sharp contrast to traditional 2-D clutter modeling techniques which typically include deterministic backscatter characteristics and assume constant terrain characteristics within gated range cell regions, i.e., there are no terrain height variations within range cells. External to ACE concept validation, the 3-D clutter modeling approach provides the opportunity to improve terrain classification methodology and enhance radar calibration techniques.; A unique interpolation scheme is introduced to handle poorly behaved, under-sampled 3-D data such as commonly observed in measured terrain elevation values. The interpolation algorithm uses a modified cubic spline formulation and, for nearly all terrain conditions, accurately creates closely spaced interpolated results from sparse input data. Interpolation of Digital Terrain Elevation Data (DTED) by a factor of nine, i.e. calculating 285 million values at 30 meter intervals from a data set with 90 meter intervals in 2-D, produces a zero mean Gaussian error distribution with a standard deviation of two meters in elevation over rugged mountainous regions.; A probabilistic backscatter coefficient generator is introduced which produces realistic backscatter values for various terrain types at all incidence angles. The statistical properties of the generator output, i.e., the mean and standard deviation, match measured values to the number of significant figures reported. The frequency of occurrence of the generator output closely matches measured terrain data frequency of occurrence; a Chi-Square test fails to reject the generator method at a 0.05 level of significance, indicating confidence in the results. The generator accurately reflects expected scattering characteristics from the nine programmed terrain types over the full range of variability associated with real terrain. |
