Determining position and orientation for aerial vehicle in GNSS-denied situations

1. An on-board state estimation system for an aerial vehicle, the system comprising:

a computer database that stores a pre-loaded digital elevation model (DEM) for a ground surface over which the aerial vehicle is to fly;

a sensor suite comprising one or more sensors, wherein the one or more sensors comprise:

an altitude sensor for sensing an above-ground altitude of the aerial vehicle;

one or more downward-pointed cameras such that the one or more cameras are pointed at the ground when the aerial vehicle is in the air; and

at least one downward-pointing laser scanner such that the at least one downward-pointing laser scanner is pointed at the ground surface when the aerial vehicle is in the air;

means, responsive to the sensor suite, for determining local, relative, continuous state estimates of the aerial vehicle as it moves, wherein the means for determining the local, relative, continuous state estimates comprise:

a visual odometry (VO) system that is in communication with the one or more downward-pointed cameras and the altitude sensor, wherein the VO system continuously computes updated local state estimates of the aerial vehicle by comparing time-stamped ground surface images taken at different points in time, using the sensed altitude of the aerial vehicle from the altitude sensor for scaling the time-stamped ground surface images; and

an inertial measurement unit (IMU) that is in communication with the one or more motion sensors and continuously measures acceleration of the aerial vehicle in three dimensions and angular velocities for roll, pitch and yaw for the aerial vehicle based on input from motion sensors that detect motion of the vehicle;

means, responsive to the sensor suite, for determining global, absolute, noncontinuous state estimates of the aerial vehicle as it moves, wherein the means for determining the global, absolute, noncontinuous state estimates comprise terrain referenced navigation means; and

state estimation means for determining continuously updated state estimates for the aerial vehicle as it moves without a need for GNSS coordinates by combining the local, relative, continuous state estimates with the global, absolute, noncontinuous state estimates.

2. The on-board state estimation system of claim 1 , wherein the state estimation means comprises a Kalman filter.

3. The on-board state estimation system of claim 1 , wherein the terrain referenced navigation means determines the global, absolute, noncontinuous state estimates of the aerial vehicle by comparing a DEM generated from data points from laser scans from the at least one downward-pointing laser scanner to the pre-loaded DEM stored in the computer database to find a sufficient match.

4. The on-board state estimation system of claim 3 , wherein the state estimation means comprises a Kalman filter.

5. The on-board state estimation system of claim 4 , wherein the terrain referenced navigation means uses a current state estimate of the aerial vehicle to constrain searching of the pre-loaded DEM to find a sufficient match between the pre-loaded DEM and the DEM generated from the data points from the laser scans.

6. The on-board state estimation system of claim 4 , wherein the at least one downward-pointing laser scanner comprises at least one 2D laser scanner.

7. The on-board state estimation system of claim 4 , wherein the at least one downward-pointing laser scanner comprises a moveable laser scanner that points downward at the ground surface for a sufficient period of time for the terrain referenced navigation means while the aerial vehicle moves.

8. The on-board state estimation system of claim 4 , further comprising a GNSS receiver, wherein the state estimation means further uses GNSS coordinates from the GNSS receiver, when available, to determine the continuously updated state estimates for the aerial vehicle as it moves.

9. An aerial vehicle comprising:

a sensor suite that comprises one or more sensors, wherein the one or more sensors comprise:

an altitude sensor for sensing an above-ground altitude of the aerial vehicle;

one or more downward-pointed cameras such that the one or more cameras are pointed at the ground when the aerial vehicle is in the air; and

at least one downward-pointing laser scanner such that the at least one downward-pointing laser scanner is pointed at the ground surface when the aerial vehicle is in the air; and

an inertial measurement unit (IMU) that is in communication with the one or more motion sensors and continuously measures acceleration of the aerial vehicle in three dimensions and angular velocities for roll, pitch and yaw for the aerial vehicle based on input from motion sensors that detect motion of the vehicle; and

a computer system in communication with the sensor suite, wherein the computer system comprises:

a computer database that stores a pre-loaded digital elevation model (DEM) for a ground surface over which the aerial vehicle is to fly;

at least one processor; and

at least one memory unit that stores software that is executed by at least one processor, wherein the software comprises:

a visual odometry (VO) module that that continuously computes updated local state estimates of the aerial vehicle by comparing time-stamped ground surface images taken at different points in time by the one or more downward-pointed cameras, using a sensed altitude of the aerial vehicle from the altitude sensor for scaling the time-stamped ground surface images;

a terrain referenced navigation module that determines global, absolute, noncontinuous state estimates of the aerial vehicle by comparing a DEM generated from data points from laser scans of the ground surface by the at least one downward-pointing laser scanner to the pre-loaded DEM stored in the computer database to find a sufficient match; and

a state estimation module for determining continuously updated state estimates for the aerial vehicle as it moves without a need for GNSS coordinates by combining the local, continuous state estimates from the VO module with outputs from the IMU and with the global, absolute, noncontinuous state estimates from the terrain referenced navigation module.

10. The aerial vehicle of claim 9 , further comprising a guidance system, wherein the continuously updated state estimates for the aerial vehicle from the state estimation module are input to the guidance system.

11. The aerial vehicle of claim 9 , further comprising a computerized navigational system, wherein the continuously updated state estimates for the aerial vehicle from the state estimation module are input to the computerized navigational system.

12. The aerial vehicle of claim 11 , wherein the state estimation module comprises a Kalman filter.

13. The aerial vehicle of claim 12 , wherein the aerial vehicle comprises a rotorcraft.