Raytheon Company

John T Broad

Lee M Savage

William Hale Wellman

A method for improving geolocation accuracy in a passive radar warning receiver, using synchronized data curve-fit and interpolation to asynchronous and noisy receiver and navigation measurements over observation periods that are extended to reduce inaccuracies caused by noise. The present disclosure yields synchronized data samples at intervals short enough that constant-rate equations are valid, even though the actual motions over the observation interval may be more complex and have higher-order dynamics. It reduces noise, synchronizes data samples, and is readily adapted to motions with variable acceleration. The method generates rate samples short enough to satisfy constant rate assumptions, yet fit data over intervals long enough to enhances measurement accuracy by reducing measurement noise.

Geolocating a remote emitter

A method for determining a FDOA of a pulsed waveform received by two sensors includes obtaining a respective plurality of in-phase and quadrature-phase (IQ) samples indicative of a pulse envelope of the received pulsed waveform. The method includes determining a TDOA responsive to a leading edge of a pulse of the pulsed waveform and obtaining a first cross correlation of IQ samples at a delay (d) closest to the TDOA, and respective second and third cross correlations at least one additional delay (d+1 and d&#x2212;1) on either side of the closest delay. The method includes refining the approximation of the TDOA according to an interpolation of amplitudes of the cross-correlation and determining a respective rate of change of cross-correlation phase (&#x394;&#x3c6;). The method includes approximating a straight line fit to the rates of change of cross-correlation phase (d&#x394;&#x3c6;/dt), the slope of the straight line representative of the FDOA.

Frequency difference of arrival (FDOA) for geolocation

A direct geolocation approach for estimating a location of a stationary emitter located on the Earth surface is provided. The approach uses data collected during a plurality of time periods including Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA) measurements of a radar pulse sent from the emitter, and altitude measurements of an aircraft above the Earth surface. The approach includes estimating a location of the emitter for each of the time periods based on the TDOA, FDOA, and altitude measurements associated with a respective time period. The estimated location of the stationary emitter includes possible longitude and latitude of the emitter. The approach further includes averaging the estimated locations associated with the plurality of time periods to form an averaged estimated location of the emitter. A convenient example of the approach computes the location of the emitter based on the averaged estimated location.

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Santa Barbara, CA, United States of America

John T Broad