# US 11,029,159 B2 · Navigation system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,029,159 B2 - Document ID: US11029159B2 - Status: Granted - Kind: B2 - Application number: 16/564,784 - Filed: 2019-09-09 - Published: 2020-04-16 - Granted: 2021-06-08 - Earliest claimed: 2018-10-15 - Assignees: Atlantic Inertial Systems Limited - Applicants: Atlantic Inertial Systems Limited - Inventors: Geoffrey Thomas Henderson - Web page: https://patentgrep.com/patent/US11029159B2 ## CPC - G01C 21/005: {with correlation of navigation data from several sources, e.g. map or contour matching (G01C21/30 takes precedence)} - G01C 21/20: Instruments for performing navigational calculations (G01C21/24, G01C21/26 take precedence) - G01C 3/08: Use of electric radiation detectors - G01C 21/1652: {with ranging devices, e.g. LIDAR or RADAR} - G01S 17/06: Systems determining position data of a target - G01S 17/87: Combinations of systems using electromagnetic waves other than radio waves - G01S 17/933: of aircraft or spacecraft - G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S) - 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 terrain-based navigation system include at least three laser range finders, each fixedly mounted to a vehicle body, each pointing in a different direction and arranged such that they can be used to calculate terrain gradient in two dimensions. Existing terrain-based navigation systems for aircraft that use a radar altimeter to determine the distance of the vehicle from the ground make use of the large field of view of the radar altimeter. The first return signal from the radar altimeter may not be from directly below the aircraft, but will be interpreted as being directly below the aircraft, thereby impairing the chances of obtaining a terrain match, or impairing the accuracy of a terrain match. The use of a plurality of laser range finders each fixedly mounted to the vehicle body allows more terrain information to be obtained as the terrain can be detected from the plurality of different directions. ## Claims ### Claim 1 A terrain-based navigation system comprising: at least three laser range finders, each fixedly mounted to a vehicle body, each pointing in a different direction and arranged such that they can be used to calculate terrain gradient in two dimensions; and a processor arranged to: receive range data from each of the laser range finders; receive attitude data on the attitude of the vehicle body, process the range data and the attitude data to generate terrain profile information; and correlate the terrain profile information with stored terrain map data to estimate a position of the vehicle body. ### Claim 2 (depends on 1) A terrain-based navigation system as claimed in claim 1, wherein the angle between the directions of at least two of the laser range finders is no more than 30 degrees. ### Claim 3 (depends on 1) A terrain-based navigation system as claimed in claim 1, wherein the angle between the directions of at least two of the laser range finders is at least 5 degrees. ### Claim 4 (depends on 3) A terrain-based navigation system as claimed in claim 3, wherein the direction of each laser range finder is at an angle of at least 5 degrees from each other laser range finder. ### Claim 5 (depends on 1) A terrain-based navigation system as claimed in claim 1, wherein beam directions of the least three laser range finders are not co-planar. ### Claim 6 (depends on 1) A terrain-based navigation system as claim 1, wherein three laser range finders are arranged at a vertex of a notional tetrahedron and each of the three laser range finders is directed along a different edge of the notional tetrahedron. ### Claim 7 (depends on 1) A terrain-based navigation system as claimed in claim 1, further comprising a processor arranged to receive range data from each of the laser range finders and to use the range data together with known angles between the directions of the laser range finders to calculate terrain gradient data. ### Claim 8 (depends on 1) A terrain-based navigation system as claimed in claim 1, further comprising an inertial navigation system arranged to provide the attitude data. ### Claim 9 (depends on 1) A terrain-based navigation system as claim 1, wherein the navigation system has no radar altimeter. ### Claim 10 (depends on 1) A vehicle comprising: a vehicle body; and a terrain-based navigation system as claimed in claim 1, wherein the laser range finders are fixedly attached to the vehicle body. ### Claim 11 A method of estimating a location of a vehicle, comprising: obtaining range data from each of at least three laser range finders, each pointing in a different fixed direction; obtaining attitude data for the vehicle; processing the range data and the attitude data to generate terrain gradient information; and correlating the terrain gradient information with stored terrain map data to estimate a location of the vehicle. ### Claim 12 (depends on 11) A method as claimed in claim 11, wherein the attitude data is obtained from an inertial navigation system. ### Claim 13 (depends on 11) A method as claimed in claim 11, wherein generating terrain gradient information comprises using the range data together with known angles between the directions of the laser range finders; and wherein the correlating step comprises correlating the terrain gradient information with the stored terrain map data to estimate a location of the vehicle. ### Claim 14 (depends on 11) A method as claimed in claim 11, wherein the directions of the at least three laser range finders are not co-planar.