Multiplatform ambiguous phase circle and TDOA protection emitter location
First Claim
1. A method for determining the geolocation of a stationary emitter using at least a first and a second moving observer, the method comprising the steps of:
- receiving first and second emitter signals, respectively, at the first and second moving observers;
measuring the ambiguous phase difference between the first and second signals at corresponding update intervals;
estimating the greatest and least possible integer value of the ambiguous phase difference, the integer values comprising a set of possible ambiguity integers;
performing pulse time-of-arrival (TOA) measurements of the emitter signal received by the observers over a predetermined clock interval;
using the TOA measurements performed by the observers to calculate the time-difference-of-arrival (TDOA) of corresponding, same-pulse, emitter signals;
generating a family of circular lines of position (LOPs) for each observer based on the ambiguous phase differences measured and the integer values estimated, wherein with no measurement error the emitter would lie on exactly one of the circular LOPs associated with each observer;
computing hyperbolic LOPs based on the TDOA calculations; and
determining emitter location utilizing the intersection of the hyperbolic LOPs generated from the TDOA measurement, and circular LOP data.
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Abstract
A method and system for determining the geolocation--i.e., the latitude, longitude, and altitude--of a stationary RF signal emitter from two or more moving observer aircraft. The observers receive signals from the emitter and the system measures the phase difference between the signals. The observers then perform pulse time of arrival (TOA) measurements over a predetermined clock interval, and calculate the time difference of arrival (TDOA) of corresponding, same-pulse, emitter signals. Based on geometric relationships, the system creates a series of circular lines of position (LOPs) for each observer, and computes hyperbolic LOPs based on the TDOA calculations. The system determines emitter location from the intersection of the hyperbolic LOPs and the circular LOPs.
65 Citations
12 Claims
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1. A method for determining the geolocation of a stationary emitter using at least a first and a second moving observer, the method comprising the steps of:
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receiving first and second emitter signals, respectively, at the first and second moving observers; measuring the ambiguous phase difference between the first and second signals at corresponding update intervals; estimating the greatest and least possible integer value of the ambiguous phase difference, the integer values comprising a set of possible ambiguity integers; performing pulse time-of-arrival (TOA) measurements of the emitter signal received by the observers over a predetermined clock interval; using the TOA measurements performed by the observers to calculate the time-difference-of-arrival (TDOA) of corresponding, same-pulse, emitter signals; generating a family of circular lines of position (LOPs) for each observer based on the ambiguous phase differences measured and the integer values estimated, wherein with no measurement error the emitter would lie on exactly one of the circular LOPs associated with each observer; computing hyperbolic LOPs based on the TDOA calculations; and determining emitter location utilizing the intersection of the hyperbolic LOPs generated from the TDOA measurement, and circular LOP data. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A system to geolocate a stationary emitter and comprising, as a minimum, two moving observers, both of whom measure the ambiguous phase change of the emitter between two positions on each of their flight paths, and two observers, possibly stationary or possibly the same observers performing the phase measurements, to measure emitter same-pulse time-of-arrival, comprising on each moving observer
first and second antennas for generating first and second emitter detection signals containing ambiguous phase information, phase difference detection circuitry and memory to store the ambiguous phase thus detected between emitter updates, these updates typically being from one half to several seconds apart, means to difference these stored and ambiguous phase differences and means to estimate the largest and smallest possible integer value of the phase change ambiguity, a navigation system and association means providing the moving observer position at the start and end of the emitter update measurement, and the spatial location of the first and second antenna, and comprising on the possibly stationary observers, a clock on each observer having a one day stability of at least 10-11 second per day, means to adjust these clocks on two observers so that they are in temporal phase with one another, a data link to command the second observer to perform a pulse time-of-arrival (TOA) measurement during a predetermined clock interval, TOA measurement means on each observer, means to form the time-difference-of-arrival (TDOA) from these same-pulse TOA measurements, and including at a site possibly distinct from any observer, but data linked to the observers, computing means to derive initial emitter geolocation from the TDOA and phase-circle LOP estimates, including means to measure received signal amplitude on two or more antennas to determine the correct coarse location from a set of statistically equally likely estimates, means to measure the signal direction of arrival from the observer position at each phase measurement update and the initial emitter position estimate, means to predict the LBI phase from the estimated DOA and known LBI baseline position, means to employ this predicted phase to differentially resolve all the LBI ambiguous phase measurements between the first and final moving observer positions simultaneously for both observers, means to cone correct the measured resolved phase using the elevation found from the estimated DOA, a polarimeter to measure emitter polarization during the LBI phase measurement, calibration means to remove polarization induced phase errors from the resolved and cone corrected measured phase using a calibration table where the phase calibration data in the table is a function of DOA and emitter polarization, and is accessed using the computed DOA and measured polarization, computing means to rederive emitter geolocation from the TDOA and cone phase-circle LOP estimates generated from the corrected phase data, predictive means employing this refined location to verify the pulse TOA measured at each relevant observer is the same pulse from the same emitter, and corrective means to remeasure TDOA if it is not.
Specification