Time delay passive ranging technique

A method of passive ranging and geolocation of a emitter that interrogates an object, which object is actively responsive to the interrogation of the emitter, and wherein the internal response times of the emitter and the object are known, said method comprising the steps of:

• detecting an active first interrogation signal from the emitter;
• starting a reference timer;
• measuring a first bearing (.theta..sub.1) to the emitter;
• detecting an active first reply signal from an answering object that is responsive to the first interrogation signal and recording the time of detection;
• computing a first time delay (.tau..sub.1) between the first interrogation signal and the first reply signal;
• measuring a second bearing (.theta..sub.2) to the answering object;
• detecting an active second interrogation signal from the emitter that is responsive to the first reply signal and stopping the reference timer;
• computing a second time delay (.tau..sub.2) between the active first reply signal and the second interrogation signal;
• computing a platform angle (.alpha.) between the emitter and the answering object;
• computing a relative range (R.sub.T) between the emitter and the answering object;
• computing a first range (R) to the emitter;
• and
• computing a second range (D) to the answering object.

A method of passive ranging and geolocation based on signal emanations from multiple objects, said method comprising the steps of:

• detecting an interrogation signal from a first object;
• starting a reference timer;
• measuring a first bearing (.theta..sub.1) to the first object;
• searching for a first echo signal that is the interrogation signal reflected from a second object;
• detecting the first echo signal and stopping the reference timer;
• measuring a first time delay (.tau..sub.1) between the interrogation signal and the first echo signal;
• measuring a second bearing (.theta..sub.2) to the second object;
• detecting an active reply signal from the second object;
• re-starting the reference timer;
• searching for a second echo signal that is the active reply signal of the second object reflected from the first object;
• detecting the second echo signal and stopping the reference timer;
• measuring a second time delay (.tau..sub.2) between the active reply signal and the second echo signal;
• computing a platform angle (.alpha.) between the first object and the second object in accordance with a first predefined relationship;
• computing a relative range (R.sub.T) between the first object and the second object in accordance with a second predefined relationship;
• computing a second range (D) to the second object in accordance with a third predefined relationship;
• and
• computing a first range (R) to the first object in accordance with a fourth predefined relationship.