# US 8,354,951 B2 · Short baseline helicopter positioning radar for low visibility > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,354,951 B2 - Document ID: US8354951B2 - Status: Granted - Kind: B2 - Application number: 12/768,793 - Filed: 2010-04-28 - Published: 2010-12-30 - Granted: 2013-01-15 - Earliest claimed: 2009-05-07 - Assignees: Intelligent Sciences, Ltd. - Applicants: Jacques Y. Guigné; James A. Stacey; Nicholas G. Pace - Inventors: Jacques Y. Guigné; James A. Stacey; Nicholas G. Pace - Web page: https://patentgrep.com/patent/US8354951B2 ## CPC - G01S 13/878: {Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector (G01S13/874 takes precedence)} - G01S 13/913: {for landing purposes} - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES ## Abstract A method for determining position and orientation of a rotating wing aircraft (e.g. helicopter) with respect to a ground station includes transmitting an electromagnetic signal from the aircraft. The signal includes a plurality of electromagnetic signals, each signal having a different selected frequency. The signal is detected at an array of sensors disposed on the ground surface in a selected pattern. The array includes at least one reference sensor and at least three spaced apart time difference determination sensors. A difference in arrival time of the signals between the reference sensor and each of the time difference determination sensors is determined and a spatial position of the aircraft is determined from the time differences. ## Claims ### Claim 1 A method for determining position of an aircraft with respect to a ground station, comprising: transmitting a signal from the aircraft, the signal comprising a plurality of electromagnetic signals, each signal having a different selected frequency, wherein transmission of each frequency is followed by a time interval of no transmission such that multiple path signals have decreased in amplitude by a predetermined amount; detecting the signals at an array of sensors disposed on the ground surface in a selected pattern, the array including at least one reference sensor and at least three spaced apart phase difference determination sensors; determining a difference in phase of the signals between the reference sensor and each of the phase difference determination sensors by determining a relationship between frequency and phase difference between signals detected by the reference sensor and each time difference determination sensor at each of a plurality of frequencies without using a time reference between sensors; and determining a spatial position of the aircraft from the time differences. ### Claim 2 (depends on 1) The method of claim 1 wherein the phase difference determination sensors are disposed on a circle having a selected radius from a position of the reference sensor. ### Claim 3 (depends on 1) The method of claim 1 wherein more than four difference determination sensors are used, and such sensors are arranged in a regular, irregular or random array geometry. ### Claim 4 (depends on 1) The method of claim 1 wherein the selected pattern of the spaced apart time difference determination sensors comprises a circle having a radius such that the phase difference does not exceed the value 2π when the aircraft is within a predetermined distance from the array. ### Claim 5 (depends on 1) The method of claim 1 further comprising deploying the array of sensors from the aircraft prior to landing thereof. ### Claim 6 (depends on 1) The method of claim 1 further comprising measuring an altitude of the aircraft at a plurality of spaced apart positions and a geodetic orientation of the aircraft thereof, and calibrating an altitude determined from the spatial position using the measured altitudes. ### Claim 7 A method for determining position of an aircraft with respect to a ground station, comprising: transmitting a signal from the ground station, the signal comprising a plurality of electromagnetic signals, each signal having a different selected frequency, wherein transmission of each frequency is followed by a time interval of no transmission such that multiple path signals have decreased in amplitude by a predetermined amount; detecting the signals at an array of sensors disposed on the aircraft in a selected pattern, the array including at least one reference sensor and at least three spaced apart phase difference determination sensors; determining a difference in arrival time of the signals between the reference sensor and each of the phase difference determination sensors by determining a relationship between frequency and phase difference between signals detected by the reference sensor and each time difference determination sensor at each of a plurality of frequencies without using a time reference between sensors; and determining a spatial position of the aircraft from the time differences. ### Claim 8 (depends on 7) The method of claim 7 wherein the phase difference determination sensors are disposed on a circle having a selected radius from a position of the reference sensor. ### Claim 9 (depends on 8) The method of claim 8 wherein the selected radius is such that the phase difference does not exceed the value 2π when the aircraft is within a predetermined distance from the array. ### Claim 10 (depends on 7) The method of claim 7 further comprising measuring an altitude of the aircraft at a plurality of spaced apart positions and a geodetic direction thereof, and calibrating an altitude determined from the spatial position using the measured altitudes. ### Claim 11 A method for determining position of an aircraft with respect to a ground station, comprising: transmitting a signal from the aircraft, the signal comprising a plurality of electromagnetic signals, each signal having a different selected frequency; detecting the signals at an array of sensors disposed on the ground surface in a selected pattern, the array including at least one reference sensor and at least three spaced apart time difference determination sensors, the array deployed from the aircraft prior to landing; determining a difference in arrival time of the signals between the reference sensor and each of the time difference determination sensors; and determining a spatial position of the aircraft from the time differences. ### Claim 12 (depends on 11) The method of claim 11 wherein the time differences are determined by determining a relationship between a frequency of the signal and a phase difference between signals detected by each of the sensors. ### Claim 13 (depends on 11) The method of claim 11 wherein the time difference determination sensors are disposed on a circle having a selected radius from a position of the reference sensor. ### Claim 14 (depends on 11) The method of claim 11 wherein more than four difference determination sensors are used, and such sensors are arranged in a regular, irregular or random array geometry. ### Claim 15 (depends on 11) The method of claim 11 wherein the selected radius is such that the phase difference does not exceed the value 2π when the aircraft is within a predetermined distance from the array.