Position surveillance using one active ranging satellite and time of arrival of a signal from an independent satellite
First Claim
1. A method of position surveillance using a plurality of satellites having known locations and including a first satellite that transmits timing signals, comprising the steps ofreceiving at an object to be located and at a fixed earth station the timing signal transmitted by said first satellite,performing a two-way active range measurement after reception of said first satellite timing signal at the earth station by transmitting an active ranging signal from the earth station through a second satellite to the object and back, to thereby derive the ranging time between said second satellite and object,measuring the time of arrival of said first satellite timing signal at the object relative to reception of said active ranging signal at the object and deriving the elapsed time interval therebetween, and transmitting said elapsed time interval to the earth station,computing at the earth station the position fix of said object from the known locations of said first and second satellites and earth station, the elapsed time interval measured at the object, and the ranging time between said second satellite and object, and displaying the position fix so obtained.
2 Assignments
0 Petitions
Accused Products
Abstract
The position of a ship or other object being located is determined at an earth station using an active ranging satellite and a satellite which transmits time signals. One line of position is determined by two-way active ranging through the first satellite. The other line of position is determined by one-way ranging from the second satellite. The time interval between the time of arrival of the timing signal at the ship and reception of the active ranging signal at the ship is measured and sent back to the earth station with the ship'"'"'s active ranging response. The position fix is then computed at the earth station.
55 Citations
12 Claims
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1. A method of position surveillance using a plurality of satellites having known locations and including a first satellite that transmits timing signals, comprising the steps of
receiving at an object to be located and at a fixed earth station the timing signal transmitted by said first satellite, performing a two-way active range measurement after reception of said first satellite timing signal at the earth station by transmitting an active ranging signal from the earth station through a second satellite to the object and back, to thereby derive the ranging time between said second satellite and object, measuring the time of arrival of said first satellite timing signal at the object relative to reception of said active ranging signal at the object and deriving the elapsed time interval therebetween, and transmitting said elapsed time interval to the earth station, computing at the earth station the position fix of said object from the known locations of said first and second satellites and earth station, the elapsed time interval measured at the object, and the ranging time between said second satellite and object, and displaying the position fix so obtained.
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6. A method of position surveillance using first and second satellites having known locations comprising the steps of
receiving at an object to be located and at a fixed earth station a timing signal transmitted by said first satellite, performing a two-way active range measurement after reception of said timing signal at the earth station by transmitting an active ranging signal from the earth station through said second satellite to the object and back through said second satellite to the earth station, and measuring at least the two-way ranging time between transmission and reception of said active ranging signal at the earth station, measuring the time of arrival of said timing signal at the object relative to reception of said active ranging signal at the object and deriving the elapsed time interval therebetween, and transmitting said elapsed time interval through said second satellite to the earth station, and supplying at least the two-way ranging time, the elapsed time interval measured at the object, and data on the locations of said first and second satellites and earth station to a computer for computation of the position fix of the object to be located.
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9. A method of position surveillance using a plurality of satellites having known locations and including a timing signal satellite that transmits timing signals at precisely known intervals, comprising the steps of
receiving at an object to be located and at a fixed earth station the timing signal transmitted by said timing signal satellite, performing a two-way active range measurement in response to reception of said timing signal at the earth station by transmitting an active ranging signal through an active ranging satellite to the object and back through said active ranging satellite to the earth station, and measuring at least the two-way ranging time between transmission and reception of said active ranging signal at the earth station to thereby derive the range from said second satellite to the object, measuring the time of arrival of said timing signal at the object relative to reception of said active ranging signal at the object and deriving the elapsed time interval therebetween, and transmitting the elapsed time interval through said active ranging satellite to the earth station, computing a line of position of the object with respect to said active ranging satellite from the known locations of said earth station and active ranging satellite and the one-way ranging time from said active ranging satellite to the object, computing a line of position of the object with respect to said timing signal satellite from the known locations of said active ranging and timing signal satellites and earth station, the elapsed time interval measured at the object, and the range from said active ranging satellite to the object, determining the position fix of said object at the intersection of said lines of position, and displaying the position fix so obtained.
Specification