Flight path optimization for resolution and coverage in synthetic aperture radar

Abstract

Synthetic-aperture radar (SAR) images have two principal dimensions: down-range and cross-range. Resolution in the down-range direction is determined by the transmitted frequency bandwidth, while resolution in the cross-range direction is determined by the angular aperture over which the target is viewed by the radar. In order to improve the resolution in these dimensions, one may increase the bandwidth of the system (frequency diversity) or increase the range of aspect angles to view the target (geometric diversity).

With the objective functional specified, we define a method for parameterizing and generating a flight-path to interrogate the scene of interest. The functional is then used as a means for determining optimal flight-paths for desired coverage and resolution objectives.

To investigate geometric diversity and the trade-off between resolution and coverage, we develop a mathematical tool to quantify the attainable resolution of the target scene. This tool involves the data-collection manifold (DCM) whose volume corresponds directly to the image resolution at a point. Adding together these manifold contributions for each target gives us an objective functional that is determined by resolution and scene coverage.

In most applications, the radar must operate within a fixed and specified frequency band, so frequency diversity is not feasible. To exploit geometric diversity, one may fly around the target of interest or steer the radar antenna towards the desired target. Both of these methods extend the observation time of the target, but in order to focus on a single target, one neglects other potential regions of interest. This demonstrates a fundamental trade-off between the resolution of a scene and the observational coverage of that scene.