Precision SAR Targeting Using Stereoscopy and RGPS aboard a UAV

Abstract

An emerging need for timely and precise poor weather targeting in support of long range weapons is identified. A conceptual system capable of all-weather imaging, target identification, target location, and precision guidance is described. This system is largely an integration of currently available technologies that can dramatically increase the accuracy of guided munitions that utilize the Global Positioning System (GPS). The central element of the system is a high-performance SAR that can quickly localize a target and take two 4-in. resolution spotlight images, within a large performance envelope. The two images are taken from the same aspect, with the single exception of a measured squint angle variance. This variance produces a distinct layover difference that can be exploited with stereoscopic (stereo) SAR algorithms to solve the range/height ambiguity and generate three-dimensional coordinate maps of a composite, orthorectified image of the target scene. These coordinates are subsequently relayed to a standard GPS-guided munition, modified to incorporate a datalink. A specially designed Relative GPS (RGPS) algorithm accounts for the separate navigation solution spaces of the sensor and the weapon and solves for GPS positions that maximize the commonality of the bias errors between the two platforms. Flight testing of the stereo SAR targeting and mock relative guidance show promising results.