Airborne surveillance method and system
First Claim
1. In an environment having at least one rotating interrogation signal source, a method of locating the position of at least one target object carrying an interrogation signal responsive transponder from an observer object located remotely from said interrogation signal source, the positions of the observer object, target object and interrogation signal source forming a geometrical arrangement, comprising:
- (a) determining the direction of said interrogation signal source by direction finding on said interrogation signal to develop source direction data;
(b) determining the direction to a said target object by direction finding on a transponder signal produced by said transponder to develop target direction data;
(c) assembling additional available data relevant to relative positions of said objects and/or said interrogation signal source, said additional data being selected to form a data set best suited to develop a present position estimate of said target object in the present geometrical arrangement;
(d) developing a present position estimate of said target object based on said direction data and said data set of additional data; and
(e) developing a present position value of said target object by using a past position value to modify the present position estimate including varying the degree of modification based on a value associated with said present position value;
said steps (d) and (e) performing the continuous tracking of target object position through geometrical arrangements where the target object position is not readily observable from a single interrogation signal source to allow full time tracking of said target object even when transmitting responses to interrogation signals from only a single interrogation signal source independent of said geometrical arrangement.
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Accused Products
Abstract
An airborne surveillance method and system allows an observer aircraft to determine the position and change of position of a multiplicity of target aircraft and thus allows analysis of collision threats from these aircraft. The system uses a phase comparison direction finding antenna to determine direction of nearby ground based SSRs and all target aircraft of interest. The system further makes use of all other available data including Mode C transponder generated altitude information of the target aircraft, the altitude of the observer aircraft, the received signal strength of both the SSR beam and the received transponder signal, the time difference of arrival between the SSR interrogation signal and the response from the target aircraft, and a variety of other factors to determine the position of the target aircraft. The system compensates for the attitude of the observer aircraft and performs optimal Kalman filtering on the input data set to produce an estimate on target position based upon prior estimates and upon information contained in the data set while making estimates of the error magnitude of each measurement and compensating for these errors. The covariance matrix Q of the Kalman filter is adaptively vaired so as to optimize the estimate of the degree of correlation between various input values.
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Citations
26 Claims
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1. In an environment having at least one rotating interrogation signal source, a method of locating the position of at least one target object carrying an interrogation signal responsive transponder from an observer object located remotely from said interrogation signal source, the positions of the observer object, target object and interrogation signal source forming a geometrical arrangement, comprising:
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(a) determining the direction of said interrogation signal source by direction finding on said interrogation signal to develop source direction data; (b) determining the direction to a said target object by direction finding on a transponder signal produced by said transponder to develop target direction data; (c) assembling additional available data relevant to relative positions of said objects and/or said interrogation signal source, said additional data being selected to form a data set best suited to develop a present position estimate of said target object in the present geometrical arrangement; (d) developing a present position estimate of said target object based on said direction data and said data set of additional data; and (e) developing a present position value of said target object by using a past position value to modify the present position estimate including varying the degree of modification based on a value associated with said present position value; said steps (d) and (e) performing the continuous tracking of target object position through geometrical arrangements where the target object position is not readily observable from a single interrogation signal source to allow full time tracking of said target object even when transmitting responses to interrogation signals from only a single interrogation signal source independent of said geometrical arrangement. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. In an environment having at least one rotating interrogation signal source, a method of locating the position of at least one target object carrying an interrogation signal responsive transponder from an observer object comprising:
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(a) determining the position of the observer object with respect to said interrogation signal source; (b) determining the direction of said target object by direction finding on said transponder to develop a target direction vector; (c) determining the speed of rotation of said interrogation signal source; (d) calculating the angle theta swept by said interrogation signal between said observer object and target object from the speed of rotation of said interrogation signal source; (e) determining the vertical altitude of said target object from a transmission developed from the target aircraft transponder; said altitude of said target aircraft, angle theta and direction to the target aircraft from the observer aircraft forming elements of data; (f) determining the degree of accuracy of each element of said data and developing an error estimate associated with each said data element; (g) developing an estimate of the present position of said target aircraft relative to said observer aircraft from the altitude of said target aircraft, the angle theta and the direction to said target aircraft from said observer aircraft; said step (g) of developing utilizing said error estimates in determining the weight to be attributed to each said data element in developing said present position estimate; (h) developing a present position value of said target object by using a past position value to modify the present position estimate including varying the degree of modification based on a value associated with said present position value. - View Dependent Claims (15, 16, 17, 18)
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19. In an environment having at least one rotating interrogation signal source, a method of locating the position of at least one target object carrying an interrogation signal responsive transponder from an observer object comprising:
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(a) determining the time difference of arrival between receipt of the interrogation signal by said observer object and receipt of an interrogation response generated by the transponder of the target object; (b) calculating Kappa, the sum of the distance from the interrogation signal source to the target object and the distance between said observer object and said target object minus the distance between the interrogation signal source and the observer object from said time difference of arrival; (c) establishing an observer aircraft plane of the observer object; (d) determining the direction of said target object by direction finding on said transponder to develop a target direction vector; (e) determining the intersections of an ellipsoid described by Kappa and a plane containing said target direction vector normal to said observer aircraft plane to form first and second target object current solutions; (f) developing a present position value by using a past position value of each said solution to modify its associated target object current solution to determine first and second present position values of said target aircraft; (g) monitoring said first and second solutions to detect improper divergence and discarding the one of said first and second solutions determined to be clearly erroneous thereby allowing tracking of said target object even when transmitting responses without attitude information in response to interrogation signals from a single interrogation signal source.
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20. A method of tracking from an observer aircraft the position of at least one target aircraft transmitting a response to an interrogation radar signal from an interrogation radar positioned remotely from said observer aircraft comprising:
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(a) selecting various data criteria relevant to the position of said target aircraft including criteria obtained from the target aircraft'"'"'s response to the interrogation radar signal; (b) accumulating measured data values from each said data criteria; (c) estimating the error of each of said data values to develop data value error estimates; (d) developing a present position estimate of said target object and an associated position error estimate from said data values and data value error estimates; and (e) developing a present position value of said target aircraft by using a past position value of the position of said target aircraft to modify the present position estimate including varying the degree of modification based on the position error estimate to optimize the developed position value. - View Dependent Claims (21, 22, 23, 24, 25, 26)
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Specification