Precise bearings only geolocation in systems with large measurements bias errors

• US 5,526,001 A
• Filed: 02/01/1995
• Issued: 06/11/1996
• Est. Priority Date: 12/11/1992
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Litton Systems Incorporated
• Inventors: Dangle, Kurt M., Rose, Conrad M.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US08/383,669
• Time in Patent Office: 496 Days
• Field of Search: 342/417, 342/420, 342/449, 342/428, 342/424, 342/450
• US Class Current: 342/442
• CPC Class Codes: G01S 1/026 of associated receivers
• CPC Class Codes: G01S 3/023 Monitoring or calibrating
• CPC Class Codes: G01S 3/32 derived from different combinations of signals from separate antennas, e.g. comparing sum with difference
• CPC Class Codes: G01S 5/0249 Determining position using measurements made by a non-stationary device other than the device whose position is being determined
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: G01S 7/021 Auxiliary means for detecting or identifying radar signals or the like, e.g. radar jamming signals

Abstract

Bearing rate of change, or equivalently bearing differences, are used to estimate emitter geolocation, in contrast to using such rates or differences to estimate only range. In using the bearing differences, it is not necessary to maintain the same relative bearing to compensate for DOA dependent errors. Nor does the invention require a precise fully resolved and calibrated interferometer to generate DF measurements. Furthermore, it can be used with currently implemented amplitude DF systems that employ no phase interferometry at all. By making minimal changes, these systems will produce accurate geolocation. The invention will also work with any system that can be modified to produce an accurate bearing rate-of-change. Therefore, it can be used with time-difference-of-arrival (TDOA) systems also. If bearing measurements are also produced by such systems, the magnitude of the bias on that bearing measurement is not important. The effect of angle bias errors in performing bearings-only geolocation are greatly reduced or eliminated. Bias and random components of the measurement error are separated, an estimation of bias error in azimuth or AOA measurements can also be generated. Bearings differences are uniquely associated with curves, e.g. circles, on which the emitter must lie. A plurality of circles are generated to unamibiguously determine emitter geolocation. Multiple platforms may be used to generate the bearing differences. It is also possible to utilize existing bearings-only emitter location software by generating psuedo bearings. The new pseudo bearing measurements use bearing differences, rather than AOA. Geolocation is thus derived strictly from bearing differences, thus eliminating the effects of bias error.

Claims

1. An apparatus for separating slowly varying systematic error in emitter bearing measurements from rapidly varying random error comprising:

means for varying the bearing measurement sample times to convert the slowly varying systematic error to an approximately fixed bias between individual updates;

means for removing the approximately fixed bias by differencing or differentiating the bearing measurements;

means for generating a new bearing measurement without bias; and

means for processing the new bearing measurement to obtain geolocation.

2. A geolocation apparatus using ambiguous phase measurements to locate an emitter without requiring DOA measurements having the same relative bearings, comprising:

an unresolved, uncalibrated interferometer having at least first and second antennas for generating first and second emitter detection signals containing ambiguous phase information;

phase comparison circuitry for comparing said phase information from said first and second detection signals and thereby producing phase difference signals;

means for converting said phase differing signals to signals representing unambiguous emitter angular bearing differences, comprising;

a. means for postulating at least one estimated emitter position to create a pseudo-bearing,

b. means for processing aircraft position information with unit vectors to generate signals representing a predicted vector,

c. a phase resolver receiving said signals representing predicted vectors and phase information to produce an azimuth signal,

d. a finite impulse response differentiator receiving said azimuth signal and outputting a differentiated signal,

e. an integrator receiving said differentiated signal and having an integration output and

f. means receiving said integration output for hypothesis testing, said means producing a signal representing a change in azimuth; and

means for generating emitter geolocation signals from said emitter angular bearing differences.

3. The apparatus defined in claim 2 wherein said phase comparison circuity comprises circuits for determining said phase difference from said first and second detection signals on inphase and quadrature channels.

4. A geolocation apparatus using ambiguous phase measurements to locate an emitter without requiring DOA measurements having the same relative bearing, comprising:

an unresolved, uncalibrated interferometer having at least first and second antennas for generating first and second emitter detection signals containing ambiguous phase information;

phase comparison circuitry for comparing said phase information from said first and second detection signals and thereby producing phase difference signals;

means for converting said phase difference signals to signals representing unambiguous emitter angular bearing differences comprising;

a. means for postulating at least one estimated emitter position to create a pseudo-bearing,

b. means for processing aircraft position information with unit vectors to generate a signal representing a predicted vector,

c. a phase resolver receiving said signals representing predicted vectors and phase information to produce an azimuth signal,

d. an AOA/LBI range processor having range filters and processing means to rapidly converge to a stable range estimate output signal,

e. means receiving said range estimate output signal for hypothesis and

f. means receiving said integration output for hypothesis testing said means producing a signal representing a change in azimuth and

means for generating emitter geolocation signals from said emitter angular bearing differences.

5. The apparatus recited in claim 4 wherein said phase comparison circuitry comprises circuits for determining said phase difference from said first and second detection signals on inphase and quadrature channels.