Study of low frequency FOPEN imaging.

Abstract

FOliage PENetration (FOPEN) imaging is the Synthetic Aperture Radar (SAR) imaging for foliage penetration application to image the targets concealed by foliage areas, which is of special interests for both military and civilian applications [1]. Usually FOPEN SAR is in spotlight mode, wherein radar beam is continually steered to image an area. Spotlight SAR has an advantage over the strip-map SAR in terms of its resolution. To provide higher resolution, UWB waveform and large integration angle are required in FOPEN radar. However, they will induce very large range migration and bring new complexities and challenges to the traditional SAR research. So some hypotheses are not valid and some classical techniques cannot be applied at all. In this thesis, two relatively novel SAR imaging algorithms, namely the back-projection algorithm and range migration algorithm, are studied. As well, a new approach of range migration algorithm is developed. In their application to FOPEN SAR imaging, performance comparison is made by theoretical analysis, simulation and experimental results. It will be shown that both of these two algorithms are suitable for FOPEN radar imaging where theoretical imaging results can be achieved. The thesis also presents some aspects of image formation in both image (spatial time) domain and phase history (spatial frequency) domain. These two domains are Fourier pair and go through the basis of image reconstruction of FOPEN SAR. In addition, some enhancement techniques for improving the quality of the reconstructed SAR image are introduced and a system model for understanding the SAR imaging process is given in the thesis. Finally, the thesis discusses some possible future research work on FOPEN SAR imaging.