System and method for navigational determination using range-doppler radar altimetry
View Patent ↗The technologies described herein relate to computing position of an aircraft, such as latitude/longitude coordinates, based upon range and Doppler measurements generated by a range-Doppler radar sensor system. The range-Doppler radar system irradiates an area below an airborne aircraft with radar signals and detects return signals that have reflected from a surface of the earth. The range-Doppler radar system generates range and Doppler measurements based upon the detected return signals. Range measurements are assigned to Doppler bins based upon the Doppler measurements that correspond to the range measurements, and range measurements are selected from the Doppler bins based upon the values of the range measurements. The selected range measurements are employed to identify positions on a digital terrain map that represents the surface of an environment. The position of the aircraft is computed based upon the identified positions on the digital terrain map.
1 . A system for determining the position and velocity of an object in flight over an environment having a surface having a plurality of known ranges relative to some datum representing the contour of the surface, the system including:
a range-doppler radar system (RDRS) couplable to an object in flight, wherein the RDRS comprises:
an antenna; and
processing circuitry that is in communication with the antenna, wherein the processing circuitry is configured to perform acts comprising:
causing the antenna to emit a plurality of radar signals towards the surface of the environment as the object is flying over the surface of the environment;
receiving a plurality of electrical signals, each that is representative of a radar return detected by the antenna, wherein each radar return is based upon a radar signal reflecting from the surface of the environment;
computing a plurality of range measurements and doppler measurements for a plurality of doppler bins from the plurality of electrical signals;
determining a plurality of minimum range measurements for each of the plurality of doppler bins, the plurality of minimum range measurements forming a minimum range contour (MRC); and
transmitting the plurality of plurality of minimum range measurements forming the MRC and corresponding doppler measurements to a computing system; and
a computing system that computes the position and velocity of the object based on a received plurality of minimum range measurements forming the MRC and corresponding doppler measurements and the known ranges representing the contour of the surface of the environment controlling a mechanical system of the object in flight based upon the computed position and velocity.
2 . The system of claim 1 , wherein the computing system that computes the three dimensional (3-D) position and 3-D velocity of the object based on a received plurality of minimum range measurements forming the MRC and corresponding doppler measurements and the known ranges representing the contour of the surface of the environment.
3 . The system of claim 1 , wherein the computing system that computes the position, the velocity, and attitude of the object based on a received plurality of minimum range measurements forming the MRC and corresponding doppler measurements and the known ranges representing the contour of the surface of the environment.
4 . The system of claim 1 , wherein the computing system that computes the 3-D position, the 3-D velocity, and the 3-D attitude of the object based on a received plurality of minimum range measurements forming the MRC and corresponding doppler measurements and the known ranges representing the contour of the surface of the environment.
5 . The system of claim 2 , wherein the RDRS is nadir-pointed.
6 . The system of claim 3 , the RDRS further including a second antenna, and the processing circuitry in communication with the second antenna and further configured to perform acts of:
receiving a plurality of second electrical signals, each that is representative of a radar return detected by the second antenna, wherein each radar return is based upon a radar signal reflecting from the surface of the environment;
computing a plurality of second range measurements and second doppler measurements for a second plurality of doppler bins from the plurality of electrical signals; and
assigning cross-track angle measurements based on the first and second plurality of range measurements.
7 . The system of claim 1 , wherein the computing system further:
computes an estimate of the plurality of minimum range measurements forming the MRC and the corresponding doppler measurements; and
determines a differential between the estimates and the received plurality of minimum range measurements forming the MRC and the corresponding doppler measurements.
8 . The system of claim 7 , wherein the computing system:
computes an estimate of a plurality of minimum range measurements forming the MRC and the corresponding doppler measurements based on one of previously received pluralities of minimum range measurements forming the MRC and the corresponding doppler measurements, outputs of a GPS receiver, and outputs of an inertial sensor system.
9 . The system of claim 7 , wherein the computing system;
computes an estimate of a plurality of minimum range measurements forming the MRC and the corresponding doppler measurements based on previously received pluralities of minimum range measurements forming the MRC and the corresponding doppler measurements and outputs of an inertial sensor system.
10 . The system of claim 9 , wherein the computing system:
computes an estimate of the position and velocity of the object; and
computes the position and velocity of the object based on the determined differential and the estimates of the position and velocity.
11 . The system of claim 10 , wherein the computing system:
employes a Kalman filter to process the determined differential; and
computes the position and velocity of the object based on the Kalman processed determined differential and the estimates of the position and velocity.
12 . The system of claim 10 , wherein the computing system:
employes an extended Kalman filter to process the determined differential; and
computes the position and velocity of the object based on the extended Kalman processed determined differential and the estimates of the position and velocity.
13 . The system of claim 10 , wherein the computing system computes an estimate of the position and velocity of the object based on the outputs of an inertial sensor system.
14 . The system of claim 12 , wherein the computing system:
computes an estimate of the 3-D position and 3-D velocity of the object; and
computes the 3-D position and the 3-D velocity of the object based on the determined differential and the estimates of the 3-D position and 3-D velocity.
15 . The system of claim 14 , wherein the computing system:
employes a Kalman filter to process the determined differential; and
computes the 3-D position and 3-D velocity of the object based on the Kalman processed determined differential and the estimates of the 3-D position and 3-D velocity.
16 . The system of claim 14 , wherein the computing system:
employes an extended Kalman filter to process the determined differential; and
computes the 3-D position and 3-D velocity of the object based on the extended Kalman processed determined differential and the estimates of the 3-D position and 3-D velocity.
17 . The system of claim 12 , wherein the computing system:
computes an estimate of the position, the velocity, and the attitude of the object; and
computes the position, the velocity, and the attitude of the object based on the determined differential and the estimates of the position, the velocity, and the attitude.
18 . The system of claim 17 , wherein the computing system:
employes an extended Kalman filter to process the determined differential; and
computes the position, the velocity, and the attitude of the object based on the Kalman processed determined differential and the estimates of the position, the velocity, and the attitude.
19 . The system of claim 14 , wherein the computing system:
computes an estimate of the 3-D position, the 3-D velocity, and the 3-D attitude of the object; and
computes the 3-D position, the 3-D velocity, and the 3-D attitude of the object based on the determined differential and the estimates of the 3-D position, the 3-D velocity, and the 3-D attitude.
20 . The system of claim 19 , wherein the computing system;
employes an extended Kalman filter to process the determined differential; and
computes the 3-D position, the 3-D velocity, and the 3-D attitude of the object based on the Kalman processed determined differential and the estimates of the 3-D position, the 3-D velocity, and the 3-D attitude.