Velocity and attitude estimation using an interferometric radar altimeter

1. A method for estimating velocity of an aircraft, the method comprising:

transmitting a beam toward a surface from the aircraft using a Doppler beam sharpened radar altimeter;

receiving a plurality of reflected signals that correspond to portions of the transmitted beam that are reflected by the surface;

forming a plurality of Doppler beams by filtering the received signals;

computing a complex-valued array of range bin with respect to frequency of the Doppler beams from at least one antenna aperture of the radar altimeter;

estimating a range for each of the Doppler beams; and

estimating a velocity vector magnitude for the aircraft by a curve fit of the range with respect to the frequency of the Doppler beams.

2. The method of claim 1 , wherein the estimated velocity vector magnitude comprises a real-time estimate of velocity of the aircraft over water.

3. The method of claim 1 , further comprising determining an estimated uncertainty based on a range variation across the Doppler beams.

4. The method of claim 1 , wherein an angle above horizon is used to calculate a vertical velocity.

5. The method of claim 1 , further comprising:

estimating interferometric phase angles for each of the Doppler beams using at least two antenna apertures of the radar altimeter; and

estimating a velocity vector horizontal direction of the aircraft based on the interferometric phase angles of the Doppler beams.

6. The method of claim 1 , further comprising:

estimating interferometric phase angles for each of the Doppler beams using at least two antenna apertures of the radar altimeter; and

computing an attitude of the aircraft based on the interferometric phase angles of the Doppler beams.

7. The method of claim 1 , further comprising correcting the velocity vector magnitude based on a terrain slope of the surface.

8. The method of claim 5 , further comprising correcting the velocity vector horizontal direction based on a terrain slope of the surface.

9. The method of claim 6 , further comprising correcting the attitude of the aircraft based on a terrain slope of the surface.

10. The method of claim 1 , further comprising estimating an angle above horizon for the aircraft by a curve fit of the range with respect to the frequency of the Doppler beams.

11. A computer program product, comprising:

a non-transitory computer readable medium having instructions stored thereon executable by a processor to perform a method for estimating velocity of an aircraft according to claim 1 .

12. A system for estimating velocity of an aircraft, the system comprising:

at least one processor in the aircraft; and

a processor readable medium having instructions stored thereon executable by the processor to:

transmit a beam toward a surface from the aircraft using a Doppler beam sharpened radar altimeter;

receive a plurality of reflected signals that correspond to portions of the transmitted beam that are reflected by the surface;

form a plurality of Doppler beams by filtering the received signals;

compute a complex-valued array of range bin with respect to frequency of the Doppler beams from at least one antenna aperture of the radar altimeter;

estimate a range for each of the Doppler beams; and

estimate a velocity vector magnitude for the aircraft by a curve fit of the range with respect to the frequency of the Doppler beams.

13. The system of claim 12 , wherein the processor readable medium has further instructions stored thereon executable by the processor to:

estimate interferometric phase angles for each of the Doppler beams using at least two antenna apertures of the radar altimeter; and

estimate a velocity vector horizontal direction of the aircraft based on the interferometric phase angles of the Doppler beams.

14. The system of claim 12 , wherein the processor readable medium has further instructions stored thereon executable by the processor to:

estimate interferometric phase angles for each of the Doppler beams using at least two antenna apertures of the radar altimeter; and

compute an attitude of the aircraft based on the interferometric phase angles of the Doppler beams.

15. The system of claim 12 , wherein the processor readable medium has further instructions stored thereon executable by the processor to correct the velocity vector magnitude based on a terrain slope of the surface.

16. A method for estimating attitude of an aircraft, the method comprising:

transmitting a beam toward a surface from the aircraft using a radar altimeter;

receiving a plurality of reflected signals that correspond to portions of the transmitted beam that are reflected by the surface;

estimating a range to a closest point on the surface;

computing at least one interferometric phase angle between at least two antenna apertures of the radar altimeter at the range to the closest point on the surface; and

estimating at least one component of aircraft attitude using the at least one interferometric phase angle.

17. The method of claim 16 , wherein the at least one component of aircraft attitude includes a pitch angle or a roll angle.

18. The method in claim 16 , further comprising correcting the estimated at least one component of aircraft attitude based on a terrain slope of the surface.

19. A computer program product, comprising:

a non-transitory computer readable medium having instructions stored thereon executable by a processor to perform a method for estimating attitude of an aircraft according to claim 16 .