Microwave ISAR Signature Extraction

Abstract

Global and reliable reconnaissance using remote sensing techniques requires a weather and time independent detection, recognition, and identification capability for objects under interest. A spaceborne high resolution SAR system in a spotlight mode can be an appropriate instrument. The availability of representative radar data from ground measurements is important because of the analysis, the understanding and simulation of complex target signatures and for reference signatures for automatic target recognition (ATR) purposes. Inverse SAR (ISAR) imaging allows the collection of very precise high-resolution radar signatures from objects. For a spaceborne radar system the imaging geometry is similar and differs only by geometrical transformation and rotation. With ISAR a high spatial resolution in the decimetre range is accomplished by rotating an object on a turntable with respect to a spatially fixed broadband radar system within a specific azimuth angle area. Once the radar imaging of the target has been performed, an ATR approach is required to extract a maximum of interesting information. In order to investigate the ATR capabilities and the performance, we selected a template matching method. This recognition approach is designed to be tolerant with respect to moderate differences between test and training data. A principal advantage is given by the robustness against artificially removed or produced new scattering centres. Today, the effort for building up a data base is still tremendous, by measurements as well as by simulations. An approach for limiting the overall effort is enabled by the identification of robust scattering centre locations on a typical target of interest, thus determining those target parts being worthwhile for further efforts in the simulation. Therefore specific tower-turntable ISAR measurements are undertaken for generating three-dimensional datasets by spanning a synthetic aperture not only in azimuth, but also in elevation.