Terrain referenced navigation-adaptive filter distribution

A terrain referenced navigation aircraft position determination method comprising the steps of:

• (a) predicting the line of flight of an aircraft and estimating a circle error of probability around the line of flight;
• (b) estimating a position in the center of the circle as the position of the aircraft;
• (c) distributing a plurality of kalman filter positions evenly throughout the circle error of probability and deleting those kalman filter positions from the circle error of probability which correspond with a water position;
• (d) assigning to each position of the circle error of probability five coordinates comprising altitude, an East or West velocity, an East or West acceleration, a South or North velocity, and a South or North acceleration;
• (e) assigning a latitude and longitude to each kalman filter position in the circle error of probability;
• (f) predicting the altitude, East or West velocity, East or West acceleration, South or North velocity, and South or North acceleration of the aircraft for each point in the circle error of probability;
• (g) measuring the actual altitude, East or West velocity, East or West acceleration, South or North velocity, and South or North acceleration at each point in the circle error of probability;
• (h) computing the difference between the actual and predicted altitude, East or West velocity, East or West acceleration, South or North velocity, and South or North acceleration at each point in the circle error of probability;
• (i) implementing a kalman filter algorithm on the five coordinates to estimate the latitude, longitude and altitude from the five coordinates;
• (j) using the estimate of latitude, longitude and altitude to determine a most divergent filter;
• (k) removing the most divergent filter from the circle error of probability;
• and
• (l) waiting for the line of flight to advance a predetermined distance and if advanced by the predetermined distance, repeating steps (a) through (l) until a last filter is obtained.

A terrain referenced navigation system based on a kalman filter algorithm, wherein the terrain referenced navigation system comprises:

• (a) means for processing data according to a kalman filter algorithm including a plurality of kalman filters;
• (b) means for distributing the plurality of kalman filters in an even grid describing a circle error of probability having grid points wherein each grid point includes a kalman filter and one of the kalman filters is a most divergent filter;
• and
• (c) means for removing those kalman filters from the circle error of probability which correspond to a water position and for then removing a most divergent kalman filter from the circle error of probability wherein the most divergent kalman filter is removed from the circle error of probability during every pass of the algorithm.

A terrain referenced navigation aircraft position determination apparatus comprising:

• (a) means for predicting the line of flight of an aircraft and estimating a circle error of probability around the line of flight;
• (b) means for estimating a position in the center of the circle error of probability as the position of the aircraft;
• (c) means for distributing kalman filter positions evenly throughout the circle error of probability and for removing those kalman filters from the circle error of probability which correspond to a water position;
• (d) means for assigning to each position of the circle error of probability five coordinates comprising altitude, an East or West velocity, an East or West acceleration, a South or North velocity, and a South or North acceleration;
• (e) means for assigning a latitude and longitude to each kalman filter position in the circle error of probability;
• (f) means for predicting the altitude, East or West velocity, East or West acceleration, South or North velocity, and South or North acceleration of the aircraft for each point in the circle error of probability;
• (g) means for measuring the actual altitude, East or West velocity, East or West acceleration, South or North velocity, and South or North acceleration at each point;
• (h) means for computing the difference between the actual and predicted altitude, East or West velocity, East or West acceleration, South or North velocity, and South or North acceleration;
• (i) means for implementing a kalman filter algorithm on the five coordinates to estimate the latitude, longitude and altitude from the five coordinates;
• (j) means for determining a most divergent kalman filter based upon the estimate of latitude, longitude and altitude;
• (k) means for removing the most divergent kalman filter from the circle error of probability;
• and
• (l) means for waiting for the line of flight to advance a predetermined distance and if advanced by a predetermined distance, repeating steps (a) through (l) until a last kalman filter is obtained.