10.1 Introduction

Normally, SAR data is acquired by transmitting a periodic sequence of pulses, which are processed into a continuous image. This is referred to as the "stripmap" imaging mode. However, not all the transmitted pulses are needed to form a continuous image. In Chapter 9, it is shown that if an image with a low resolution in azimuth is acceptable, gaps can exist between sections of the acquired data, as illustrated in Figure 9.7. If the radar system is operated in this mode, a burst of pulses is transmitted, corresponding to the time of FFT 1 in Figure 9.7. The transmitter is then turned off until the time of FFT 2 is reached. These ON/OFF cycles are repeated during the data collection period. This type of SAR operation is referred to as "burst mode" operation.

Burst mode was first used in the Magellan mission to Venus in 1990, to conserve transmit power and downlink capacity [1]. However, if these restrictions do not apply, the radar system can use the gaps to collect additional information [2, 3]. As an example, the gaps can be used to illuminate other range swaths, where low resolution images can also be formed. By stitching these images together, a wide swath image is obtained, which covers a range extent that is impossible to image with conventional SAR operation. Another example is the acquisition of data from other polarizations during the gaps.

This mode is called "ScanSAR." It is included in most modern satellite SAR systems...