Aircraft navigation system - uses simple correlation of surface images with several comparison images with different grey stale thresholds

摘要

The aircraft navigation system has two memories for two-dimensionial reference and measured images of the earth's surface in digital form. The position of the aircraft w.r.t. the surface is determined by correlation of the reference and measurement images. A simple correlation procedure is used. For each individual reference image point only the information black or white is stored. Several comparison images are derived from the sensor output. The points of these images are also stored as black or white. The different comparison images have different grey scale threshold levels to distinguish between black and white points. At least one comparison image is correlated with the reference. The correlation function used is that for which the main to side lobe ratio is a maximum.