Boeing Aerospace Company (BAC) of Seattle, Washington and Sperry Microwave Electronics of Clearwater, Florida have developed a multiple -beam radiometric navigation update system. This paper describes the system design, flight test program, and preliminary results. The system was designed and its performance evaluated using analytically derived formulas for performance measures and detailed Monte Carlo simulations. As a result BAC recommended a five or seven fixed beam radiometer.Sperry built a seven -beam, 35 GHz radiometer which BAC flight tested in 1979 to demonstrate its effectiveness over a variety of test scenes under various environmental conditions. Four scenes were selected for the flight test varying from land -water to highly forested regions.Preliminary analysis of the flight test results confirm the expected performance improvement over the single-fixed -beam system tested in 1975. This approach to a terrain sensing millimeter wave radiometer would be applicable to low altitude penetrating aircraft.The system is low cost, with no moving parts; low volume, requiring only a single receiver with small wide -beam antennas; and stealthy, being completely passive.Radiometry can also be complementary to todays terrain correlation approach since flat areas usually contain a maximum of cultural features; where one system works poorly the other works well.This test program provides a data base for studying a wide variety of pattern matching and correlation algorithms, with and without attitude compensation, and using various subsets of the full seven -beam combination.
The Department of Defense has applications for radiometric navigation update systems and thus an ongoing need for improved radiometric reference map preparation procedures: more automatic procedures that produce more widely applicable data bases. An existing radiometric reference map preparation procedure is described that involves screening suitable navigation update sites, preparing temperature maps, and validating the temperature maps. The screening is partly manual (a photo interpreter looks for radiometrically unstable boundaries or insufficient spatial detail) and partly automatic (a computer evaluates the proportions of various materials).Temperature maps are automatically prepared from material region maps which are prepared by a photo interpreter tracing boundaries and identifying materials. Mission tape (temperature map) validation is by detailed simulation. We recommend replacing the manual screening techniques with automatic boundary evaluation. Instead of manual boundary tracing and material identification, we recommend region growing and boundary extraction techniques.Reference maps are needed since a radiometric navigation update system compares (using pattern matching or correlation) a sensed scene with a prestored reference map to estimate position.The terrain sensor detects energy reflected and emitted by the ground in portions of the millimeter wave band (usally at 35 or 94 GHz).
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