Methods and apparatus for optimizing interferometric radar altimeter cross track accuracy

• US 6,731,236 B1
• Filed: 06/11/2003
• Issued: 05/04/2004
• Est. Priority Date: 06/11/2003
• Status: Expired due to Term

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Hager, James R., Almsted, Larry D., Jordan, Lavell
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US10/459,137
• Time in Patent Office: 328 Days
• Field of Search: 342/165, 342/173, 342/174, 342/120, 342/121, 342/122, 342/123
• US Class Current: 342/174
• CPC Class Codes: G01S 13/4454 phase comparisons monopulse, i.e. comparing the echo signals received by an interferometric antenna arrangement
• CPC Class Codes: G01S 13/882 for altimeters measuring height using barometric means G01C5/06
• CPC Class Codes: G01S 7/4021 of receivers
• CPC Class Codes: G01S 7/4065 involving a delay line

Abstract

An apparatus for calibrating a radar altimeter is described. The altimeter provides an angle to a target based on radar energy received at right, left, and ambiguous antennas. The apparatus comprises a turntable on which the radar is mounted, a turntable controller which controls positioning of the radar altimeter, a radar energy source receiving transmit signals from the radar altimeter, a reflector, and a calibration unit. The reflector reflects and collimates radar energy from the radar source towards the radar altimeter. The calibration unit receives an angle from the controller indicative of a position of the radar altimeter with respect to the collimated radar energy and a measured angle from the radar altimeter. The calibration unit calculates a correction based on differences between the angle received from the turntable and the measured angle received from the altimeter and provides the calibration correction to the altimeter.

Claims

1. An apparatus for calibrating an interferometric radar altimeter, the radar altimeter providing an interferometric angle to a target based on radar energy received at a right antenna, a left antenna, and an ambiguous antenna located between the right and left antennas, said apparatus comprising:

a turntable on which the radar altimeter is mounted;

a turntable controller which controls positioning of the radar altimeter on said turntable;

a radar source receiving transmit signals from the radar altimeter;

a reflector which reflects radar energy from said radar source towards the radar altimeter on said turntable, said reflector positioned to collimate the radar energy reflected to said turntable; and

a calibration unit receiving an angle from said turntable controller indicative of an orientation of the radar altimeter with respect to the collimated radar energy and a measured angle from the radar altimeter indicative of a perceived orientation of the radar altimeter with respect to the collimated radar energy, said calibration unit calculating a radar calibration correction based on a difference between the angle received from the turntable and the measured angle received from the radar altimeter, said unit providing the calibration correction to the radar altimeter.

2. An apparatus according to claim 1 wherein said radar source comprises a transmit horn coupled to one antenna of the radar altimeter.

3. An apparatus according to claim 2 wherein said radar source further comprises a delay element.

4. An apparatus according to claim 1 wherein said calibration unit calculates the radar calibration correction based upon multiple orientations of said turntable, and multiple measured angles from the radar altimeter.

5. A method for determining discrepancies between an orientation of a radar altimeter and a measurement of the orientation by the radar altimeter, the radar altimeter having a plurality of receiving antennas, the discrepancies caused by varying delays in processing the radar returns received at each antenna, said method comprising:

mounting the radar altimeter in a known orientation;

directing a collimated radar signal towards the radar altimeter;

providing a radar measurement of an angle of the radar altimeter with respect to the collimated radar signal; and

determining a difference between an angle representative of the known orientation and the radar measurement angle.

6. A method according to claim 5 wherein said mounting comprises:

mounting the radar altimeter on a turntable whose position is controlled by a turntable controller; and

receiving the known orientation from the turntable controller.

7. A method according to claim 6 wherein said mounting the radar altimeter on a turntable comprises utilizing precision guide pins to mount a chassis of the radar altimeter to the turntable.

8. A method according to claim 5 wherein said directing comprises:

orienting a reflector to reflect collimated radar signals to the radar altimeter; and

transmitting a radar signal towards the reflector.

9. A method according to claim 5 wherein said directing comprises:

providing a transmit pulse from the radar altimeter; and

delaying the transmit pulse to simulate a radar return from a distant target.

10. A method according to claim 5 wherein providing a radar measurement comprises:

processing radar returns received at three separate antennas; and

determining an angle of the radar altimeter with respect to the collimated radar signal based on phase differences between the radar returns received at the three antennas.

11. A method for compensating a measured angle to a radar target provided by a radar altimeter, the radar altimeter including a plurality of receive antennas hard mounted to a chassis of the radar altimeter, said method comprising:

receiving a known orientation of the radar altimeter with respect to an expected radar return;

directing a collimated radar signal towards the radar altimeter;

receiving a radar measured angle resulting from the collimated radar signal;

determining a difference between an angle representative of the known orientation and the radar measured angle; and

providing radar calibration corrections to the radar altimeter, the corrections causing differences between the radar measured angle and the angle representative of the known orientation of the radar altimeter to be reduced as compared to the determined difference.

12. A method according to claim 11 wherein receiving a known orientation of the radar altimeter comprises receiving a position of a turntable on which the radar altimeter is mounted, the position indicative of an orientation of the radar altimeter with respect to the expected radar return.

13. A method according to claim 12 wherein receiving a position comprises providing a turntable angle to a calibration unit.

14. A method according to claim 11 wherein receiving a radar measured angle resulting from the collimated radar signal comprises:

outputting a radar pulse from the radar altimeter; and

delaying transmission of the radar pulse such that the received radar signal simulates a radar return from a distant target.

15. A method according to claim 14 further comprising providing a reflector which collimates the radar pulse and reflects the radar pulse towards the radar altimeter.

16. A method according to claim 11 wherein providing radar calibration corrections comprising determining calibration corrections based on a plurality of known orientations and radar measured angles which correspond to the known orientations.

17. A method according to claim 11 further comprising storing the radar calibration corrections in the radar altimeter.

18. A calibration unit receiving a radar measured angle and a turntable angle, the turntable angle indicative of an orientation of a radar altimeter with respect to a collimated radar signal, said calibration unit comprising a software code segment for calculating radar calibration corrections based on a difference between the two received angles.

19. A calibration unit according to claim 18 wherein said code segment calculates radar calibration corrections based upon a plurality of turntable angles and corresponding radar measured angles.