Position determination and message transfer system employing satellites and stored terrain map

Claims

What is claimed is:

1. A method for generating terrain map information representing local terrain elevations at a plurality of points on the earth's surface, comprising:

placing a transceiver at a position of known latitude and longitude on the earth's surface, said transceiver being operable to transmit a reply signal in response to a received interrogation signal;

transmitting an interrogation signal to said transceiver;

receiving a reply signal from said transceiver through a relay satellite at a known orbital location above the earth;

calculating the terrain elevation at the transceiver location based on the transmission time of the interrogation signal and the arrival time of the reply signal from the satellite;

entering said terrain elevation into a terrain map memory as a function of said latitude and longitude; and

moving the transceiver to a different position and repeating the foregoing method steps.

2. A method for generating terrain map information representing local terrain elevations at a plurality of points on the earth's surface, comprising:

placing a transceiver at a position of known latitude or longitude on the earth's surface, said transceiver being operable to transmit a reply signal in response to a received interrogation signal;

transmitting an interrogation signal to said transceiver;

receiving a reply signal from said transceiver through two relay satellites at spaced orbital locations above the earth;

calculating the terrain elevation and the unknown latitude or longitude of the transceiver based on the transmission time of the interrogation signal and the arrival times of the reply signal from the two satellites;

entering said terrain elevation into a terrain map memory as a function of said latitude and longitude; and

moving the transceiver to a different position and repeating the foregoing method steps.

3. A method for generating terrain map information representing local terrain elevations at a plurality of points on the earth's surface, comprising:

placing a transceiver at a random position on the earth's surface, said transceiver being operable to transmit a reply signal in response to a received interrogation signal;

transmitting an interrogation signal to said transceiver;

receiving a reply signal from said transceiver through three relay satellites at spaced orbital locations above the earth;

calculating the latitude, longitude and terrain elevation of the transceiver location based on the transmission time of the interrogation signal and the arrival times of the reply signal from the three satellites;

entering said terrain elevation into a terrain map memory as a function of said latitude and longitude; and

moving the transceiver to a different position and repeating the foregoing method steps.

4. A method for generating terrain map information representing local terrain elevations at a plurality of points on the earth's surface, comprising:

placing a transceiver at a random position on the earth's surface, said transceiver being operable to transmit a reply signal in response to a received interrogation signal, said reply signal including altitude information obtained from an altitude-sensing device associated with said transceiver;

transmitting an interrogation signal to said transceiver;

receiving a reply signal from said transceiver through two relay satellites at spaced orbital locations above the earth;

calculating the latitude, longitude and terrain elevation of the transceiver based on the transmission time of the interrogation signal, the arrival times of the reply signal from the two satellites, and the altitude information included in the reply signal;

entering said terrain elevation into a terrain map memory as a function of said latitude and longitude; and

moving the transceiver to a different position and repeating the foregoing method steps.

5. A method for providing approach guidance to a landing aircraft using two relay satellites at spaced orbital locations above the earth, said aircraft carrying a transceiver for transmitting a reply signal in response to a received interrogation signal, said method comprising the steps of:

transmitting an interrogation signal to the aircraft transceiver at a known or measured time;

receiving a reply signal from the aircraft transceiver through each of the two satellites;

calculating a line of position for the aircraft based on the arrival times of the reply signal through the two satellites and the transmission time of the interrogation signal;

determining the approximate location of the aircraft on the line of position from altitude information provided by the aircraft altimeter;

calculating a ground track between the aircraft location and an airport runway;

determining the terrain height along the ground track by reference to a stored terrain map providing local terrain elevations at a plurality of points on the earth's surface;

calculating an approach path for the aircraft based on the ground track and the terrain height information obtained from the stored terrain map; and

providing the aircraft with direction steers to assist the aircraft in following said approach path.

6. A system for determining the position of a user located on the earth's surface, comprising:

a user-carried transceiver for receiving an interrogation signal and transmitting a reply signal in response to said interrogation signal;

two satellites at spaced orbital locations above the earth, each of said satellites carrying repeater means for receiving and retransmitting the reply signal transmitted by the user-carried transceiver; and

a ground station for periodically transmitting the interrogation signal and for receiving and processing the retransmitted reply signals from the two satellites, said ground station including means for calculating the user position based on the arrival times of the retransmitted reply signals at the ground station, the transmission time of the interrogation signal from the ground station, and the elevation of the user on the earth's surface, said elevation being derived from a stored terrain map providing local terrain elevations at a plurality of points on the earth's surface;

wherein said terrain map provides terrain heights at second points spaced from input reference points on a reference ellipsoid approximating the earth's surface, said second points having horizontal positions corresponding to the intersection points between the surface of the earth and the possible lines of position established by the two satellites.

7. A method for determining the positions of a user located on the earth's surface using two relay satellites at spaced orbital locations above the earth, said user carrying a transceiver for transmitting a reply signal in response to a received interrogation signal, said method comprising the steps of:

transmitting an interrogation signal to the user at a known or measured time;

receiving a reply signal from the user through each of the two satellites;

measuring the arrival times of the reply signals received through the two satellites;

calculating a line of position for the user based on the arrival times of the reply signal through the two satellites and the transmission time of the interrogation signal; and

determining the intersection of the line of position with the earth's surface by reference to a stored terrain map providing local terrain elevations at a plurality of points on the earth's surface;

wherein the two satellites are in geostationary orbit about the earth, each of said satellites being located in a different position in said orbit, and wherein the step of determining the intersection of the line of position with the earth's surface comprises the following steps:

determining the intersection of the line of position with a reference ellipsoid approximating the earth's surface to define a reference point on said ellipsoid;

obtaining from the stored terrain map the terrain height at the reference point;

calculating the approximate intersection of the line of position with the earth's surface from the terrain height at the reference point and the known angle of the line of position with respect to the reference ellipsoid.

8. A method for determining the position of a user located on the earth's surface using two relay satellites at spaced orbital locations above the earth, said user carrying a transceiver for transmitting a reply signal in response to a received interrogation signal, said method comprising the steps of:

transmitting an interrogation signal to the user at a known or measured time;

receiving a reply signal from the user through each of the two satellites;

measuring the arrival times of the reply signals received through the two satellites;

calculating a line of position for the user based on the arrival times of the reply signal through the two satellites and the transmission time of the interrogation signal; and

determining the intersection of the line of position with the earth's surface by reference to a stored terrain map providing local terrain elevations at a plurality of points on the earth's surface;

wherein the two satellites are in geostationary orbit about the earth, each of said satellites being located in a different position in said orbit, and wherein the step of determining the intersection of the line of position with the earth's surface comprises the following steps:

determining the intersection of the line of position with a reference ellipsoid approximating the earth's surface to define a reference point on said ellipsoid; and

using the reference point as an input, obtaining from the stored terrain map the terrain height at a second point on the reference ellipsoid which is spaced from said reference point, said second point having the same horizontal position as the intersection of the line of position with the earth's surface.