METHOD AND SYSTEM FOR HIGH PRECISION ALTITUDE MEASUREMENT OVER HOSTILE TERRAIN

• US 20020126041A1
• Filed: 07/27/2001
• Published: 09/12/2002
• Est. Priority Date: 07/27/2000
• Status: Active Grant

• Current Assignee: Innovative Solutions and Support Incorporated
• Original Assignee: Innovative Solutions and Support Incorporated
• Inventors: Hedrick, Geoffrey S.M.
• Granted Patent: US 6,462,703 B2
• Time in Patent Office: Days
• US Class Current: 342/120
• CPC Class Codes: G01C 5/005 altimeters for aircraft G01C5/02, G01C5/06 take precedence
• CPC Class Codes: G01S 13/882 for altimeters measuring height using barometric means G01C5/06

Abstract

A system and method for providing highly accurate measurements of the altitude above ground level (AGL) of an aircraft flying over local terrain. A current AGL altitude of the aircraft over local terrain is obtained by activating a radar altimeter on the aircraft for a single short duration or pulse. A mean sea level (MSL) elevation of the local terrain is determined by identifying the terrain from the then-current aircraft geographical position coordinates and utilizing known terrain topography data. The actual MSL altitude of the aircraft can then be determined. An uncorrected MSL altitude of the aircraft is then determined from conventional static air pressure measurements and the difference between the actual MSL altitude and the uncorrected MSL altitude of the aircraft yields a local barometric correction factor for use in determining MSL altitude measurements of the aircraft as the aircraft flies over and continues its flight away from the local terrain.

Claims

1. A method for determining a barometric pressure corrected above mean sea level (MSL) altitude of an in-flight aircraft over terrain, comprising the steps of:

calculating a current above ground level (AGL) altitude of the aircraft by generating a single brief transmission from the aircraft directed onto local terrain over which the aircraft is currently flying and receiving at the aircraft a return reflection of the transmission;

identifying the current local terrain using then-current position coordinates of the aircraft, and determining a known MSL elevation of the identified local terrain using a source of stored terrain elevation data;

calculating an actual MSL altitude of the aircraft from the calculated AGL altitude of the aircraft and the identified MSL elevation of the local terrain;

determining an uncorrected MSL altitude estimate of the aircraft from static air pressure measurement;

calculating a local barometric correction factor for the identified local terrain from the difference of said calculated actual MSL altitude of the aircraft and said determined MSL altitude estimate of the aircraft; and

using the calculated correction factor in conjunction with continued measurement of static air pressure to determine the barometric pressure corrected MSL altitude of the in-flight aircraft proximate the identified local terrain and continuously as the aircraft proceeds in flight away from the local terrain.

2. The method of claim 1, further comprising the step of calculating, on a continuing basis after said calculating of the local barometric correction factor, the AGL altitude of the aircraft above terrain over which the aircraft is positioned as the aircraft continues in flight away from the identified local terrain by using the determined MSL altitude of the in-flight aircraft in conjunction with continued identification of newly-current position coordinates of the aircraft and the source of terrain elevation data.

3. The method of claim 1, wherein said RF transmission is a radar transmission.

4. The method of claim 3, wherein said RF transmission is a radar transmission.

7. The method of claim 1, wherein said MSL altitude of the local terrain is determined by reference to an on-board database containing values of terrain elevations.

8. The method of claim 1, wherein said step of determining an uncorrected MSL altitude estimate of the aircraft uses a temperature-corrected static air pressure measurement.

9. The method of claim 1, wherein said step of calculating an actual MSL elevation comprises adding the calculated AGL altitude of the aircraft and the identified MSL altitude of the local terrain.

10. The method of claim 1, wherein said brief transmission is no greater than about one second in duration.

5. The method of claim 5, wherein the aircraft position coordinates comprise latitude and longitude coordinates of the aircraft as determined by a Global Positioning System.

6. The method of claim 5, wherein the latitude and longitude coordinates of the aircraft are determined by inertial navigation.

11. A system for determining an above mean sea level (MSL) altitude of an in-flight aircraft over terrain, comprising:

means for calculating a current above ground level (AGL) altitude of the aircraft by generating a single brief transmission from the aircraft directed onto local terrain over which the aircraft is currently flying and receiving at the aircraft a return reflection of the transmission;

means for identifying the current local terrain using then-current position coordinates of the aircraft, and for determining a known MSL elevation of the identified local terrain using a source of stored terrain elevation data;

means for calculating an actual MSL altitude of the aircraft from the calculated AGL altitude of the aircraft and the identified MSL elevation of the local terrain;

means for determining an uncorrected MSL altitude estimate of the aircraft from static air pressure measurement; and

means for calculating a local barometric correction factor for the identified local terrain from the difference of the calculated actual MSL altitude of the aircraft and the determined MSL altitude estimate of the aircraft, wherein the calculated correction factor is used in conjunction with continued measurement of static air pressure to determine the MSL altitude of the in-flight aircraft proximate the identified local terrain and as the aircraft continues in flight away from the identified local terrain.

12. The system of claim 11, wherein said brief transmission is an RF transmission.

13. The system of claim 12, wherein said RF transmission is a radar transmission.

14. The system of claim 11, wherein the aircraft position coordinates comprise latitude and longitude coordinates of the aircraft as determined by a Global Positioning System.

15. The system of claim 14, wherein the latitude and longitude coordinates of the aircraft are determined by inertial navigation.

17. The method of claim 16, wherein said step of identifying an actual current MSL altitude of the aircraft comprises identifying the actual current MSL altitude using augmented GPS to provide the actual current MSL altitude of the aircraft over the current local terrain location.

18. The method of claim 16, wherein said step of identifying an actual current MSL altitude of the aircraft comprises the steps of:

calculating a current above ground level (AGL) altitude of the aircraft by generating a single brief signal transmission from the aircraft directed onto the current local terrain location and receiving at the aircraft a return reflection of the transmitted signal;

determining a known MSL elevation of the current local terrain location using a source of stored local terrain elevation data; and

calculating the actual current MSL altitude of the aircraft over the current local terrain location by adding the calculated current AGL attitude of the aircraft and the determined MSL elevation of the current local terrain location.

19. The method of claim 16, wherein said step of identifying an actual current MSL altitude of the aircraft comprises the steps of:

calculating a current above ground level (AGL) altitude of the aircraft by using a radar altimeter of the aircraft for generating a single brief signal transmission from the aircraft directed onto the current local terrain location and receiving at the aircraft a return reflection of the transmitted signal;

determining a known MSL elevation of the current local terrain location using a source of stored local terrain elevation data; and

calculating the actual current MSL altitude of the aircraft over the current local terrain location by adding the calculated current AGL altitude of the aircraft and the determined MSL elevation of the current local terrain location.

16. A method for determining a barometric pressure corrected above mean sea level (MSL) altitude of an in-flight aircraft over terrain, comprising the steps of:

identifying a current local terrain location over which the aircraft is currently in flight using a GPS receiver on the aircraft;

identifying an actual current MSL altitude of the aircraft over the current local terrain location using an altitude determining means not based on static air pressure measurement proximate the aircraft;

determining an uncorrected current MSL altitude of the aircraft over the current local terrain location using a static air pressure measurement proximate the in-flight aircraft;

calculating a difference between the identified actual current MSL altitude and the determined uncorrected current MSL altitude and calculating a local barometric correction factor for the current local terrain location using the calculated difference;

using the calculated correction factor in conjunction with continued measurement of static air pressure to determine the barometric pressure corrected MSL altitude of the in-flight aircraft proximate the local terrain and continuously as the aircraft proceeds in flight away from the local terrain.