Doppler Shifting Technique for Generating Multi-Frames of Video SAR via Sub-Aperture Signal Processing

Abstract

The signal processing technologies of synthetic aperture radar (SAR) have been vastly studied as diverse measurement modes for various applications. One of the technologies is Video-SAR (ViSAR). It is a land-imaging mode where a sequence of images is continuously formed on the spotlight mode. We propose a new signal processing method to generate the multi-frames of ViSAR using Doppler shifting technique via sub-aperture processing. The method is based on our designed wide-angle antenna, which is a corrugated horn shape with low side lobe and Gaussian beam pattern. This wide-angle antenna receives a wide Doppler band along the azimuth direction. Based on the characteristics of the antenna, we separate the wide Doppler band into each chirp pulse signal. Each of these separated signals has a different center time. Through each chirp pulse signal in Doppler domain, the proposed method generates each frame of video at a high frame rate. The proposed ViSAR processing can show high efficiency with low computation and without a fixed coordinate system. Moreover, it can also visualize a wider area on stripmap mode than the conventional ViSAR mode, and can derive the video results based on Range Doppler Algorithm (RDA). These advantages can lead to reduce economic costs and simplify the operating ViSAR system. We have performed the practical experiments using X-band chirp pulse SAR system mounted on an airplane to verify the proposed method.