The Secretary of State for Defence in Her Britannic Majesty's Government

General Electric Company

National Research Development Corporation

Christopher J Oliver

Ian P Finley

Richard G White

James W Wood

Robin Jones

Anthony L Freeman

David Blacknell

John M Vaughan

Shaun Quegan

Michael Alldritt

Stephen P Luttrell

Ian A Ward

Synthetic aperture radar

In a synthetic aperture radar system, information concerning the radar reflectivity of a point on the ground is placed in an image at an azimuthal (cross-range) position which corresponds to the position of zero Doppler frequency shift of the received signal, under the assumption that the antenna has followed a straight line trajectory. In practice, the antenna trajectory will undergo small deviations about this straight line path which are not taken into account in the azimuth processing and which, consequently, cause incorrect azimuthal positioning in the image of the information concerning a point target on the ground. The invention uses the value of the slope of the frequency modulation of the received signal, calculated by means of an autofocus procedure, to determine the intercept of this frequency modulation at successive azimuth positions. This true intercept value is then incorporated in the azimuth processing, instead of the assumed intercept of the frequency modulation, allowing imagery which is free from azimuthal positioning errors to be produced.

Synthetic aperture radar systems

A super resolution imaging system employing coherent radiation comprises transmitting, receiving and processing means to provide complex amplitude image data. The image data is processed by a weight function generator to provide a weight function. The weight function has values at individual image pixels consisting of a background or clutter intensity term added to a pixel intensity dependent term. The latter term is non-zero for pixel intensities exceeding a threshold level well above background. A computer generates singular functions from the weight function and system impulse response, and employs the singular functions to decompose the image data and subsequent object reconstruction. This provides enhanced resolution compared to that available from the image data alone. An iteration controller employs the reconstructed object data to iterate resolution enhancement until no significant improvement is obtained.

Super resolution imaging system

A method of, and apparatus for, processing a digital electric signal composed of a train of discrete uniformly or non-uniformly shaped pulses to recover spectral information contained in the spacings between the pulses, in which the digital signal is applied to a SAW spectrum analyzer arranged to produce output signals the envelopes of which represent the power spectrum over a selected frequency range of constituent sample lengths of the digital signal, and the required spectral information then derived from these output signals, for example by integration thereof over a period of time. The technique may be used in conjunction with a laser Doppler velocity measurement system in which each pulse of the digital signal represents the detection of a photon scattered from a moving object or particle in a scattering volume illuminated by laser light, the spacing between the pulses containing information regarding the velocity of movement of the object or particles under observation.

Processing of digital signals

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Malvern, United Kingdom

Christopher J Oliver