Airborne surveillance method and system

In an environment having at least one rotating interrogation signal source, a system of locating the position of at least one target object carrying an interrogation signal responsive transponder from an observer aircraft comprising:

• phase detecting direction finding antenna means for developing a first direction signal representative of the direction of said rotating interrogation signal source and for developing a second direction signal representative of the direction of each target object by detecting the target object's interrogation signal responsive transponder;
• means for assembling additional data relevant to relative positions of said objects and said interrogation signal source;
• means, responsive to said first and second direction signals and said additional available data, for developing a present position estimate for the relative position of each said target object;
• means for storing a past position value of each said target object;
• and
• Kalman filtering means for updating the past position value with said estimate of present position to determine a present position value of each said target object.

In an environment having at least one rotating interrogation signal source, a system of locating the position of at least one target object carrying an interrogation signal responsive transponder from an observer object positioned remotely from the rotating interrogation signal source comprising:

• phase detecting direction finding antenna means for developing a first direction signal representative of the direction of said rotating interrogation signal source and for developing a second direction signal representative of the direction of each target object by detecting the target object's interrogation signal responsive transponder;
• means for assembling additional data elements relevant to relative positions of said objects and said interrogation signal source;
• means for developing an estimate of the error of each of said first and second direction signals as well as each of said additional data elements to produce data value error estimates;
• means, responsive to said first and second direction signals, said additional available data, and said data value error estimates, for developing a present position estimate for the relative position of each said target object as well as a related position error estimate;
• means for storing a past position value of each said target object;
• and
• optimal filtering means for developing a present position value of said target by using the past position value to modify the estimate of present position to determine a present position value of each said target object, the degree of modification being based on the position error estimate to optimize the developed position value.

A method of determining the orientation of an observer object comprising:

• a) providing previous orientation information;
• b) sensing rate information related to the present state of the observer object;
• c) multiplying said previous orientation information with said rate information to obtain the present orientation rate of said observer object;
• d) integrating the present orientation rate to develop updated orientation information.