Abstract: Techniques are disclosed for determining a true bearing angle from an airborne platform to a source of a radar signal. In an embodiment, a grid is generated based on a coarse range to, and angle-of-arrival of, an electromagnetic signal. The grid represents a geographic area thought to contain the emission source. A measured spatial angle is computed for each pulse of the signal received during a data collection interval. Hypothesized spatial angles are computed for a point in each grid box in the grid. A score is generated for each grid point based on the computed hypothesized spatial angles for the grid point and the measured spatial angles. The grid point having the lowest score is identified as a seed location and is used to launch a Nelder-Mead algorithm that converges on a point in the grid. A true bearing angle to the source of a radar angle is computed to the point provided by the Nelder-Mead algorithm.

Abstract: Techniques are provided for emitter geolocation. A methodology implementing the techniques according to an embodiment includes measuring phase differences between radar signals received at one or more pairs of antennas. The method also includes calculating hypothesized phase differences based on ray tracings from hypothesized emitter locations at a first set of grid points, to the antennas. The method further includes generating scores based on correlations between the measured phase differences and the hypothesized phase differences. The method further includes generating an error ellipse based on candidate grid points associated with scores that are above a threshold. The process may be repeated on a second set of grid points, bounded by the error ellipse, to generate a second set of scores. The grid point, from the second set of grid points, that is associated with the highest of the second set of scores is selected as the estimated emitter geolocation.

Abstract: Techniques are provided for emitter geolocation. A methodology implementing the techniques according to an embodiment includes measuring phase differences between radar signals received at one or more pairs of antennas. The method also includes calculating hypothesized phase differences based on ray tracings from hypothesized emitter locations at a first set of grid points, to the antennas. The method further includes generating scores based on correlations between the measured phase differences and the hypothesized phase differences. The method further includes generating an error ellipse based on candidate grid points associated with scores that are above a threshold. The process may be repeated on a second set of grid points, bounded by the error ellipse, to generate a second set of scores. The grid point, from the second set of grid points, that is associated with the highest of the second set of scores is selected as the estimated emitter geolocation.

Abstract: Techniques are disclosed for determining AOA of one or more radar pulses received at a vehicle and originating from a source. The techniques are particularly well-suited to provide pilots with a more accurate determination of the azimuth angle to the radar source, although ground-based and water-based vehicles may benefit as well. Some embodiments discussed herein determine a true estimation of both azimuth and elevation angles, with reference to an aircraft's body-centered coordinate system, to the radar source. These parameters can also be used to determine a more accurate position on the ground for the radar source.

Abstract: Techniques are provided for geolocation of a radar emitting source. A methodology implementing the techniques according to an embodiment includes calculating time difference of arrival (TDOAs) of ground emitter radar pulses, within a dwell period, between two long baseline interferometer (LBI) antennas. The TDOA calculations are based on a precision estimate of the time of arrival of the radar pulses. The method further includes calculating an LBI phase wrap disambiguation factor based on (1) the TDOAs, (2) an average of frequencies of the radar pulses within the dwell period, and (3) an average of phase shifts of the radar pulses between the LBI antennas within the dwell period. The method further includes mapping a curve of points onto the surface of the earth based on an LBI cone angle calculation employing the LBI phase wrap disambiguation factor. The curve of points is associated with a geolocation of the ground emitter.

Abstract: Techniques are provided for geolocation of an airborne radar emitting source. A methodology implementing the techniques according to an embodiment includes initializing a search grid with hypothesized emitter geolocations boxes of the grid. The method further includes refining geolocations based on calculated pulse repetition intervals of de-Dopplerized times of arrival (TOAs) of emitter pulses received at multiple collection platforms within a dwell period. A residue metric is employed to qualify candidate target geolocations based on differences between the measured TOAs and hypothesized TOAs associated with the refined geolocations. A candidate history tracks the geolocations of the candidates with the smallest residue over subsequent dwells, identifying such candidates that match locations in the history and updating counts of times the candidate has been matched. Candidates with lagging match counts are dropped from the history.

Abstract: Techniques are provided for geolocation of an airborne radar emitting source. A methodology implementing the techniques according to an embodiment includes initializing a search grid with hypothesized emitter geolocations boxes of the grid. The method further includes refining geolocations based on calculated pulse repetition intervals of de-Dopplerized times of arrival (TOAs) of emitter pulses received at multiple collection platforms within a dwell period. A residue metric is employed to qualify candidate target geolocations based on differences between the measured TOAs and hypothesized TOAs associated with the refined geolocations. A candidate history tracks the geolocations of the candidates with the smallest residue over subsequent dwells, identifying such candidates that match locations in the history and updating counts of times the candidate has been matched. Candidates with lagging match counts are dropped from the history.

Abstract: A method of processing times-of-arrival (TOAs), some representing emitted pulses by an emitter and generated from a pulse pattern having a fixed greatest common divisor pulse repetition interval (GPRI), the method including: creating pulse trains each including an initial TOA and a vector of added TOAs, and a corresponding pulse index vector mapping the TOA vector into the pulse pattern consistent with a known TOA tolerance and viable with a known GPRI range of the emitter type; and walking, for each pulse train, each next TOA after the added TOAs, and each next index mapping the next TOA into the pulse pattern, including checking if the pulse train extended by the next TOA and next index is consistent with the TOA tolerance, checking if the extended pulse train is viable with the GPRI range, and if both checks pass, adding the next TOA and next index to the pulse train.

Abstract: A method of processing times-of-arrival (TOAs), some representing emitted pulses by an emitter and generated from a pulse pattern having a fixed greatest common divisor pulse repetition interval (GPRI), the method including: creating pulse trains each including an initial TOA and a vector of added TOAs, and a corresponding pulse index vector mapping the TOA vector into the pulse pattern consistent with a known TOA tolerance and viable with a known GPRI range of the emitter type; and walking, for each pulse train, each next TOA after the added TOAs, and each next index mapping the next TOA into the pulse pattern, including checking if the pulse train extended by the next TOA and next index is consistent with the TOA tolerance, checking if the extended pulse train is viable with the GPRI range, and if both checks pass, adding the next TOA and next index to the pulse train.

Abstract: Techniques are provided for geolocation of a radar emitting source. A methodology implementing the techniques according to an embodiment includes calculating time difference of arrival (TDOAs) of ground emitter radar pulses, within a dwell period, between two long baseline interferometer (LBI) antennas. The TDOA calculations are based on a precision estimate of the time of arrival of the radar pulses. The method further includes calculating an LBI phase wrap disambiguation factor based on (1) the TDOAs, (2) an average of frequencies of the radar pulses within the dwell period, and (3) an average of phase shifts of the radar pulses between the LBI antennas within the dwell period. The method further includes mapping a curve of points onto the surface of the earth based on an LBI cone angle calculation employing the LBI phase wrap disambiguation factor. The curve of points is associated with a geolocation of the ground emitter.

Abstract: Techniques are disclosed for determining AOA of one or more radar pulses received at a vehicle and originating from a source. The techniques are particularly well-suited to provide pilots with a more accurate determination of the azimuth angle to the radar source, although ground-based and water-based vehicles may benefit as well. Some embodiments discussed herein determine a true estimation of both azimuth and elevation angles, with reference to an aircraft's body-centered coordinate system, to the radar source. These parameters can also be used to determine a more accurate position on the ground for the radar source.

Abstract: Techniques are disclosed for selecting a closest to optimal radar/emitter location for single-ship applications. In accordance with some embodiments, given single-ship geolocation estimates are organized so that clusters of those estimates can be identified, wherein optimal solutions may be found in consecutive, adjacent segments of distance (bins) along each axis of given a coordinate system. Once the clusters are identified in each axis, an optimal cluster can be selected for each. To determine the closest answer to optimal, the coordinate data points in each of the optimal clusters can be averaged (or other sound mathematical process) for each axis in the coordinate system, so as to provide an optimal 3-D coordinate in the given coordinate system. In other embodiments, the optimal 3-D coordinate can be further used to establish an origin in a second coordinate system (e.g., for conversion from 3-D to 2-D coordinate system).

Abstract: A coherent TOA system is provided for rapidly ascertaining the position of a pulse train emitter such as a radar. Techniques are provided to estimate the underlying repetition interval of the emitter and to do the TOA processing knowing which of the particular pulses is being detected at a collector, thus surmounting the effect of gaps in the received pulse stream. The subject system is preferable to conventional time-difference-of-arrival geolocation systems which require that each of the collecting platforms measure the same pulse from the emitter, and also to non-coherent TOA systems whose accuracy is less than that achievable with the subject coherent system for the same amount of data.

Abstract: A coherent TOA system is provided for rapidly ascertaining the position of a pulse train emitter such as a radar. Techniques are provided to estimate the underlying repetition interval of the emitter and to do the TOA processing knowing which of the particular pulses is being detected at a collector, thus surmounting the effect of gaps in the received pulse stream. The subject system is preferable to conventional time-difference-of-arrival geolocation systems which require that each of the collecting platforms measure the same pulse from the emitter, and also to non-coherent TOA systems whose accuracy is less than that achievable with the subject coherent system for the same amount of data.

Abstract: A system is provided for rapidly ascertaining the position of a pulse train emitter such as a radar using multiple collectors without requiring more than one platform to measure the same pulse. Thus time-of-arrival measurements at a number of collecting platforms are performed, with the positions of the platforms being accurately ascertainable using GPS data, and with time synchronization between the spaced-apart collectors performed by utilizing atomic clocks. In the multi-ship case, geolocation can be performed on ten milliseconds of data as opposed to 30 seconds of data for measurements involving a single platform. The subject system is preferable to conventional time-difference-of-arrival geolocation systems because those systems require that each of the collecting platforms measure the same pulse from the emitter, which severely constrains the flight paths of the collectors, limits the amount of usable data, and increases the system's sensitivity requirements.