Litton Systems, Inc.

Northrop Grumman Systems Corporation

USA As Represented by Secretary of the Navy

Litton Industries, Inc.

Conrad M Rose

Jeffrey J Drude

Kurt M Dangle

William R Chadwick

A method of locating a terrestrial emitter of electromagnetic radiation in the midst of a plurality of emitters in a satellite in orbit about the earth which utilizes a location estimation and location probability determination process with respect to each possible emitter site and its corresponding error region and then using both feedback and feed forward interaction between location and phase ambiguity resolution processes to generate resolved phase from emitter location, update emitter location or some or all of the emitters, and subsequently utilizing the probabilities thus determined to produce a single estimate of the desired emitter's location.

Method for single satellite geolocation of emitters using an ambiguous interferometer array

In one embodiment, the disclosure relates to a method for estimating and predicting a target emitter's kinematics, the method including the steps of: (a) passively sampling, at a first sampling rate, an emitter signal to obtain at least one passively measured signal attribute for estimating the target kinematics; (b) inputting the passively measured signal attribute to an estimator at a first sampling rate; (c) determining a radar duty cycle for active radar measurements as a multiple of the first sampling rate, the multiple defining a duration between radar transmissions; (d) directing a radar system to make active target measurements at the determined duty cycle; (e) inputting to the estimator the active target measurements at the determined duty cycle, while continuously inputting the passively measured signal attributes.

Augmented passive tracking of moving emitter

Emitter target range and heading are estimated from bearing measurements enhancing bearings-only estimator convergence to a target track, and permitting optimization of an observer position relative to the target at the end of the total bearing measurement period. One or more estimates of the target range, speed and heading made from bearing measurements before an observer maneuver are used to determine the most appropriate observer maneuver giving complete bearings-only target-motion-analysis observability. A set of parameters characterizing a set of potential emitter signal sources is generated based on measured emitter characteristics. A most probable set of emitter platforms is identified and the emitter operating mode and corresponding platform set are associated with a kinematic regime set. A specific speed or discrete set of speeds best adapted to a set of all possible platform missions, emitter speed as a continuous function of emitter range, and emitter range are all determined.

Method for determining the optimum observer heading change in bearings-only passive emitter tracking

A method of and apparatus for passively determining agile-frequency-emitter location and computer-readable medium bearing instructions therefor. Unless a specified accuracy threshold is met or exceeded, phase, frequency, and baseline position are measured during a single receiver dwell and processed. An array of gains and phase difference ambiguity integers for all phase difference measurements are computed. An emitter DOA unit vector or COS(AOA) is estimated and an LBI phase difference is predicted. If the rank of the set of baseline-frequency product differences is greater than 1, each DOA unit vector is projected and scaled by the measured frequency corresponding to the baseline measurement. Otherwise, if the rank is 1, the product of the COS(AOA) and baseline length is formed and scaled by the measured frequency. The corresponding ambiguous measured phase difference, resolved and differenced, is used to estimate the resulting integer value and the resolved phase change and emitter range is estimated from the angle change.

Method for using signal frequency change to differentially resolve long baseline interferometer measurements

A method of estimating emitter range and heading from bearing measurements without requiring observer heading change or observer acceleration during the bearing measurement collection period. Emitter signal characteristics are measured and a set of parameters characterizing a specific emitter as a signal source are generated based on the measured characteristics. Based on the emitter characterization and an emitter-platform association data base, a most probable platform including the emitter is identified and the emitter operating mode and corresponding specific platform are associated with a particular kinematic regime. A platform performance data base is used to (1) derive a speed value based on the kinematic regime, (2) generate emitter bearings based on the measured emitter characteristics, (3) estimate the emitter speed based on the emitter bearings, and (4) determine the emitter range based on a comparison of the continuous speed value with a discrete speed value derived based on the platform performance data base.

Method of passively estimating an emitter's position and velocity using bearings-only without requiring observer acceleration

This present invention advantageously eliminates the critical deficiencies of current multipath interferometer processing demonstrated in field testing. In particular the present invention substantially improves AOA estimation accuracy and reliability when utilizing super resolution algorithms. The present invention also overcomes the data-gap drawback of data editing methods, especially for emitters at low elevations. The present invention does this by detecting phase processing errors and substituting correct AOA estimates for the corrupt ones. In the preferred implementation, the detection and substitution time extends only slightly the super resolution or data editing processing time. By thus requiring little additional processing time, the present invention allows the interferometer to output accurate angle estimates at the receiver's emitter-revisit rate for all emitter-array geometries and signal polarizations. The present invention eliminates both the gross errors caused by abnormally large phase noise variance, typically created by diffuse multipath, and the interfering signal errors induced by specular multipath.

Method and apparatus for detecting and eliminating signal angle-of-arrival errors caused by multipath

Disclosed is a method of associating a single pulse from an agile emitter with previously detected pulses from that emitter in a time interval less than the pulse repetition interval (PRI) of the radar. Ambiguous phases from the previously detected pulses from the same agile emitter are stored. A single cos(aoa) from a subset of the stored ambiguous phases is estimated. A new ambiguous phase &phgr; at frequency f , is detected. This frequency is different from at least one of the frequencies associated with the phases in the stored set. The phase measurement is made between two antennas spatially separated by distance d. A set of differenced phases is formed and corresponding differenced frequencies from the stored set, with at least one member of this set being the difference of the new ambiguous phase and frequency with one of the stored phases and its associated frequency. The phase cycle measurement ambiguity integer is measured resolving the phase difference formed from the new ambiguous phase utilizing this set of phase and frequency differences. The phase cycle measurement ambiguity integer is computed resolving the new ambiguous phase difference if the new pulse is from the same emitter as the stored set by utilizing the previously estimated cos(aoa) and newly measured frequency f . The measured and computed ambiguity integers are compared. The newly detected pulse is associated with the previously stored pulses as being from the frequency agile emitter if the integers are equal.

Apparatus and method for the monopulse linking of frequency agile emitter pulses intercepted in on single interferometer baseline

The present invention uses feedback,from RF carrier frequency measurements,to disassociate the emitter angle-of-arrival component,in the ambiguous phase measurement,from the initially unknown phase measurement integer ambiguities,; to then process,resolve the ambiguities; and finally to process,to obtain the correct emitter AOA. The present invention does this by converting the actual interferometer baselines,on which the unassociated pulse,phase measurements,were made at different emitter frequencies to a baseline set,for a single-frequency equivalent interferometer array. This conceptual array has the following property: the phase measurement,that would be made on it at the fixed frequency for a signal at the same direction-of-arrival,are identical to the actual phase measurements made on the physical array. Because of this equivalency the conceptual array is called the E(equivalent)-array. But, whereas the physical array has antenna spacings,that are invariant, the E-array &ldquo;antenna&rdquo; spacings,change as a function of the RF carrier frequency measurement feedback,which depends on the particular residual pulses being tested. Thus there is a different E-array, even for the same frequency agile emitter, depending on the particular residual pulse set,used.

Method of detection and determining an angular location of frequency agile emitters

The present invention determines the geolocation of an emitter, using at least one observer measuring signal change while moving on at least two observation tracks. The measurement of emitter signal change is begun between a first observer position and a second observer position. The second observer position is predicted at the time the last measurement from which signal change will be derived is made. The method utilizes knowledge of the measurement start and end points to determine a second pair of observer signal-change measurement start and end positions such that the emitter line-of-position (LOP) determined by the second signal change measurement will intersect the LOP associated with the first signal change measurement at possibly multiple points, but at each of these point intercept orthogonally to within the signal change measurement errors. The method determines the intersection points of the LOPs and assigns a likelihood to each intersection point for measuring the probability for each of the multiple intersection points that it is the emitter location, determines a correct emitter position from these likelihood weights, and generates an error associated with the emitter position estimate.

Method for reducing geometrical dilution of precision in geolocation of emitters using phase circles

The application measures a projectile velocity and an acceleration from radar track data. The air temperature and an air pressure are measured. The measured air temperature and the measured air pressure are extrapolated to the projectile's location for each instant in time a radar measurement made by the radar. The projectile's drag parameter is estimated at each time in the projectile's flight that the projectile's velocity and acceleration are estimated. The projectile's Mach number is estimated at each time in the projectile's flight. The drag coefficient is estimated. A functionally normalized drag parameter (FNDP) is formed. The FNDP is defined as the ratio of drag parameter of a reference projectile at each Mach number the drag is measured to the in-flight projectile's drag parameter at the corresponding Mach numbers. A weighted average of the resulting FNDP values is performed with respect to Mach number. The most likely of three regions the FNDP parameter lies is statistically determined. The relative weight of the in-flight projectile is inferred as one of light, medium or heavy based on the most likely of the three regions.

Method of and apparatus for determining the relative weight and weapon class of battlefield projectiles insensitive to errors in meteorological data and radar measurements

A method and apparatus for determining from a moving observer the location, in terms of latitude, longitude, altitude, and velocity, of a stationary or moving radar emitting a pulsed or continuous-wave signal. The moving observer extracts from the radar signal significant electronic support measures (ESM) parameters, including frequency, pulse repetition interval, and pulse width, and determines from those parameters whether a radio frequency (RF) or pulse repetition frequency (PRF) measurement technique is appropriate, and whether the radar signal angle-of-arrival (AOA) must be computed. The emitter location is computed using a ratio of sequential frequency measurements, and the moving observer continues to collect frequency measurements until the location of the emitter can be established to within a predetermined degree of certainty.

Apparatus and method for locating an emitter using RF carrier or PRF

Emitter location using RF carrier or PRF measurement ratios

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.

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Dahlgren, VA, United States of America

Conrad M Rose