Space based monitoring of global maritime shipping using automatic identification system
View Patent ↗An automatic identification system (AIS) communications payload for a space vehicle traveling in earth orbit includes an antenna; a receiver connected to the antenna to receive an AIS signal including a reported vessel position transmitted from a vessel; a processor to process the received AIS messages and determine the accuracy of the reported vessel position; and a transmitter to transmit the processed AIS messages and the determined accuracy to a ground earth element. The processor may be configured to determine a position of the space vehicle; compare the reported vessel position to the space vehicle position; and determine the accuracy of the reported vessel position based on the comparison. The processor also may be configured to flag the AIS message as suspect when the reported vessel position is determined to be inaccurate.
1. An automatic identification system (AIS) communications payload for a space vehicle traveling in earth orbit, the communications payload comprising:
an antenna;
a receiver connected to the antenna to receive an AIS signal including a reported vessel position transmitted from a vessel;
a processor to process the received AIS messages; and
to determine a position of the satellite; and
to determine a propagation delay of the signal from the vessel to the satellite; and
to determine an expected propagation delay from the vessel to the satellite based on said vessel position included in said received AIS signal and the satellite position;
comparing the propagation delay to the expected propagation delay; and
to determine the accuracy of the reported vessel position based on the comparison; and
a transmitter to transmit the processed AIS messages and the determined accuracy to a ground earth element.
2. The payload of claim 1 wherein the processor is configured to:
determine a position of the space vehicle;
compare the reported vessel position to the space vehicle position; and
determine the accuracy of the reported vessel position based on the comparison.
3. The payload of claim 1 wherein the processor is configured to flag the AIS message as suspect when the reported vessel position is determined to be inaccurate.
4. The payload of claim 2 wherein the processor is configured to use global position information for the space vehicle to determine the position of the space vehicle.
5. The payload of claim 1 wherein the processor is configured to:
determine a propagation delay of the AIS signal from the vessel to the space vehicle;
determine an expected propagation delay from the vessel to the space vehicle based on the vessel position and the space vehicle position;
compare the propagation delay to the expected propagation delay; and
determine the accuracy of the vessel position based on the comparison.
6. The payload of claim 5 wherein the processor is configured to flag the AIS message as suspect when the reported vessel position is determined to be inaccurate.
7. The payload of claim 5 wherein the processor is configured to flag the AIS message as suspect when the difference between the propagation delay and the expected propagation delay exceeds a threshold.
8. The payload of claim 5 wherein the processor is configured to determine a frequency offset from a nominal frequency and a time delay from a start a communications timing slot to determine the propagation delay.
9. The payload of claim 1 wherein the antenna is a very high frequency antenna and the communications payload is configured to travel in a low earth orbit.
10. A method to determine accuracy of AIS messages, the method comprising:
receiving an AIS message that includes a vessel position at a satellite;
determining a position of the satellite;
determining a propagation delay of the signal from the vessel to the satellite;
determining an expected propagation delay from the vessel to the satellite based on said vessel position included in said received AIS signal and the satellite position;
comparing the propagation delay to the expected propagation delay;
and determining the accuracy of the vessel position based on the comparison.
11. The method of claim 10 further comprising: flagging the message as suspect when the position is determined as inaccurate.
12. The method of claim 10 wherein determining a position of the satellite includes receiving the position of the satellite.
13. A method to determine accuracy of AIS messages, the method comprising:
receiving an AIS signal from a vessel including a vessel position at a satellite;
determining a propagation delay of the signal from the vessel to the satellite;
determining an expected propagation delay from the vessel to the satellite based on said vessel position included in said received AIS signal and the satellite position;
comparing the propagation delay to the expected propagation delay;
and determining the accuracy of the vessel position based on the comparison.
14. The method of claim 13 further comprising:
flagging the message as suspect when the position is determined as inaccurate.
15. The method of claim 13 further comprising:
flagging the message as suspect when the difference between the propagation delay and the expected propagation delay exceeds a threshold.
16. The method of claim 13 wherein determining the propagation delay includes measuring a frequency offset from a nominal frequency and a time delay from a start of a communications timing slot.