METHOD AND APPARATUS FOR MAKING AIRBORNE RADAR HORIZON MEASUREMENTS TO MEASURE ATMOSPHERIC REFRACTIVITY PROFILES

• US 20100052978A1
• Filed: 09/04/2008
• Published: 03/04/2010
• Est. Priority Date: 09/04/2008
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Tillotson, Brian J.
• Granted Patent: US 7,872,603 B2
• Time in Patent Office: Days
• US Class Current: 342/26.B
• CPC Class Codes: G01S 13/88 Radar or analogous systems specially adapted for specific applications electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00
• CPC Class Codes: G01S 13/953 mounted on aircraft
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

A method for determining a refractivity profile of an atmosphere of the Earth. The method may involve: generating radar signals from a radar device located above the Earth'"'"'s surface toward the Earth'"'"'s surface; measuring a time of flight and a reflected intensity of reflected radar signals received back at the radar device; using the measured time of flight and the reflected intensity of the reflected radar signals received by the radar device to determine a distance to a radar horizon where the radar signals are tangent to the Earth'"'"'s surface; and using the distance to the radar horizon to determine a refractivity profile of the atmosphere through which the radar signals and the reflected radar signals have travelled.

Claims

1. A method for determining a refractivity profile of an atmosphere of the Earth, the method comprising:

generating radar signals from a radar device located above the Earth'"'"'s surface toward the Earth'"'"'s surface;

measuring a time of flight and a reflected intensity of reflected radar signals received back at said radar device;

using the measured time of flight and said reflected intensity of said reflected radar signals received by said radar device to determine a distance to a radar horizon where the radar signals are tangent to the Earth'"'"'s surface; and

using the distance to the radar horizon to determine a refractivity profile of the atmosphere through which said radar signals and said reflected radar signals have travelled.

2. The method of claim 1, wherein said generating radar signals from a radar device comprises generating radar signals from a radar device located on an airborne mobile platform.

3. The method of claim 2, wherein said generating radar signals from an airborne mobile platform comprises generating radar signals from an aircraft.

4. The method of claim 1, wherein said generating radar signals from a radar device comprises generating radar signals from a radar device located at a fixed, elevated position on the Earth with the radar device having a view toward a horizon of the Earth.

5. The method of claim 1, further comprising measuring at least one of air temperature and barometric pressure in a vicinity of the radar, and using said at least one of said temperature and said barometric pressure in determining said refractivity profile.

6. The method of claim 1, further comprising assimilating said time of flight and said reflected intensity with at least one of:

measurements taken without the use of said radar signals; and

a model of atmospheric behavior,

to determine said refractivity profile.

7. The method of claim 1, wherein said generating a plurality of radar signals comprises generating a plurality of radar signals at different altitudes.

8. The method of claim 1, further comprising averaging the intensities of a subplurality of said plurality of reflected radar signals over a given range gate.

9. The method of claim 1, further comprising averaging the reflected signal intensities over a plurality of selected azimuth angles.

10. The method of claim 1, further comprising controlling an elevation angle of an antenna associated with said radar device to maximize a strength of said reflected radar signals near said horizon.

11. The method of claim 1, further comprising using a terrain database in connection with at least one of:

a location of said radar; and

geometric optics formulas;

to adjust an elevation angle of an antenna emitting said radar signals from said radar device, to account for known terrain characteristics.

12. The method of claim 1, further comprising using at least one of:

a topographic database;

an air traffic database;

an altitude-encoding transponder; and

a ship traffic database;

to determine the altitude of a first radar reflector that reflects a signal toward said radar device from beyond a radar horizon, and using the maximum distance at which said first radar reflector is detected to estimate a refractivity profile.

13. The method of claim 12, further comprising using a second radar reflector that reflects a signal toward said radar device from beyond a radar horizon, said second reflector being located at a different altitude than said first reflector, and using the maximum distances at which said first and second reflectors are detected to estimate a refractivity profile.

14. A method for determining a refractivity profile of an atmosphere of the Earth, the method comprising:

generating radar signals from a radar device located on an airborne mobile platform toward the Earth'"'"'s surface;

receiving ones of said radar signals that are reflected back to said radar device;

measuring a time of flight and a reflected intensity of said radar signals reflected back at said radar device over a plurality of range gates;

using the measured time of flight and said reflected intensity of said radar signals received by said radar device, to determine an approximate distance to a radar horizon where the radar signals are tangent to the Earth'"'"'s surface; and

assimilating the distance from the mobile platform to the radar horizon, and at least one additional measurement obtained without the use of said radar signals, to determine a refractivity profile of the atmosphere through which said radar signals have travelled.

15. The method of claim 14, wherein said generating radar signals from a radar device comprises generating a plurality of radar signals at different altitudes of said mobile platform.

16. The method of claim 14, further comprising averaging the intensities of a subplurality of said radar signals reflected back to said radar device, over a given one of said range gates.

17. The method of claim 14, further comprising controlling an elevation angle of an antenna associated with said radar device to maximize a strength of said radar signals that are reflected back to said radar device from near said horizon.

18. The method of claim 14, further comprising using a topographic database in connection with at least one of:

a location of said radar device; and

geometric optics formulas;

to adjust an estimated grazing angle of a radar signal reflected from a particular patch of terrain toward said radar device, and using said estimated grazing angle together with the measured intensity of the reflected radar signal to compute an estimated intensity of a radar signal reflected from a hypothetical patch of level terrain at the same location.

19. A system for determining a refractivity profile of an atmosphere of the Earth, the system comprising:

a radar device located at an elevated location providing a view of the Earth'"'"'s horizon, being adapted to emit radar signals toward the Earth'"'"'s surface;

a processor adapted to analyze time of flight information for ones of said radar signals reflected back to, and received by, said radar device, and adapted to determine a time of flight of flight of said radar signals to a radar horizon, the processor further being adapted to use said time of flight and information relating to an intensity of said reflected ones of said radar signals to determine a refractivity profile for a portion of an atmosphere of said Earth that said radar signals have travelled through.

20. The system of claim 19, further comprising a subsystem for measuring the position and altitude of the radar device and providing information relating thereto to said processor.

21. The system of claim 19, further comprising a subsystem that provides air temperature and barometric pressure information to said processor.

22. The system of claim 19, further comprising a network for transmitting said refractivity profile generated by said processor to a remotely located substation.