Data Level Fusion of Multilook Inverse Synthetic Aperture Radar (ISAR) Images

Although techniques for resolution enhancement in single-aspect radar imaging have made rapid progress in recent years, it does not necessarily imply that such enhanced images will improve target identification or recognition. However, when multiple looks of the same target from different aspects are obtained, the available knowledge base increases allowing more useful target information to be extracted. Physics based image fusion techniques can be developed by processing the raw data collected from multiple ISAR sensors, even if these individual images are at different resolutions. We derive an appropriate data fusion rule in order to generate a composite image containing increased target shape characteristics for improved target recognition. The rule maps multiple data sets collected by multiple radars with different system parameters on to the same spatial-frequency space. The composite image can be reconstructed using the inverse 2-D Fourier transform over the separated multiple integration areas. An algorithm called the matrix Fourier transform is created to realize such a complicated integral. This algorithm can be regarded as an exact interpolation, such that there is no information loss caused by data fusion. The rotation centers need to be carefully selected in order to properly register the multiple images before performing the fusion. A comparison of the IAR (Image Attribute Rating) curve between the fused image and the spatial-averaged images quantifies the improvement in the detected target features. The technique shows considerable improvement over a simple spatial averaging algorithm and thereby enhances target recognition.