System for sensing velocity through the use of altimetry signals

Abstract

A system for determining the relative velocity of two objects in a direction substantially transverse to a line between them wherein a first of the objects, for example an aircraft, transmits a continuous sequence of radar pulses from a broad beam antenna directed toward the ground and a receiver, also mounted on the aircraft, receives the echo returns of the pulses through an antenna which has a pair of phase center locations spaced apart in the direction of the relative velocity. The two receiving phase centers follow substantially the same ground track. Reflected pulses received at the separated phase center locations are non-coherently detected and a computing system performs a time-amplitude comparison of the pulse amplitude values detected at the aft phase center location against the pulse amplitude values detected at the forward phase center location N pulse repetition intervals earlier in time. Each set of pulse comparisons is performed according to the general relationship (F.sub.i - A.sub.N+i) (F.sub.i-2 - F.sub.i+2) and the sequence of resulting values constitutes a correlation output signal representing the error in alignment between the spatial position of the aft phase center location and the spatial position of the forward phase center location N pulse repetition intervals earlier in time. The sign of the correlation output signal represents the direction of the error. A feedback control system is provided for adjusting the repetition frequency of the transmitted pulses until the correlation output indicates minimum error. In the condition of minimum error the system operates such that each pulse received at the aft phase center location is reflected from substantially the identical area of ground terrain from which the pulse received at the forward phase center location was reflected N pulse repetition intervals earlier in time. The relative velocity between the aircraft and the ground is calculated as a function of the pulse repetition frequency. A system is also disclosed wherein the forward and aft phase center locations are alternately displaced laterally of the direction of relative velocity to enable additional detection of drift velocity.

Dependencies are inferred from the claim text.