Demonstration of SAR Distortion Correction Using a Ground-Based Multichannel SAR Test Bed

In this paper, a ground-based phased-array radar is used to investigate the ability of a multichannel synthetic aperture radar (MSAR) to produce high-fidelity images of dynamic ocean scenes by correcting the distortions caused by the motion of the water surface itself. The ground-based system, the Naval Research Laboratory Focused Phased Array Imaging Radar (FOPAIR), mimics an MSAR with multiple apertures arrayed in the flight direction by rapidly and repeatedly scanning across a linear array of 64 antenna elements. This generates a virtually unlimited time stack of coherent images in the same way that an airborne MSAR generates multiple images as the antennas fly past the scene. By manipulating a single FOPAIR data set, both undistorted “benchmark” imagery and distorted images corresponding to an airborne MSAR can be generated. More significantly, the time stack of emulated MSAR images can be processed further using the velocity synthetic aperture radar (VSAR) technique to significantly reduce the well-known but seemingly unavoidable distortions caused by surface wave motion. In this paper, VSAR is demonstrated experimentally for the first time using FOPAIR imagery of a small boat. MSAR systems with a wide range of aperture numbers are emulated, including the special case of a two-aperture system, commonly known as an along-track interferometric SAR. The results emphasize that VSAR processing does not require a long surface coherence time to produce fine-resolution imagery, unlike a single-channel SAR. The results also illustrate some limitations of VSAR as a means to measure velocity and produce high-fidelity imagery of dynamic ocean scenes.