Space based network for detection and monitoring of global maritime shipping using automatic identification system

Abstract

A spaced-based system is provided to simultaneously track and monitor one or more ocean going vessels at any point on the earth. The system includes a plurality of space vehicles or satellites each satellite includes an AIS communications payload to receive AIS signals including AIS information transmitted from the one or more vessels and to transmit the received AIS information. The system also includes a plurality of ground earth elements. Each ground earth element includes a receiver to receive the AIS information transmitted from one or more of the plurality of satellites to globally track and monitor the one or more vessels based on the AIS information received from the communications payload. The plurality of satellites are distributed in two or more orbital planes located at a substantially common altitude and having a substantially common inclination. In particular, the satellites may be deployed in a low earth orbit constellation.

1 - 19 . (canceled) 
     
     
         20 . 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 an actual value of a parameter of the signal from the vessel to the satellite; and 
 to determine an expected value of the parameter of the signal from the vessel to the satellite based on said vessel position included in said received AIS signal and the satellite position; and 
 to compare the actual value of the parameter to the expected value of the parameter; and 
 to determine the accuracy of the reported vessel position based on the comparison; and p 1  a transmitter to transmit the processed AIS messages and the determined accuracy to a ground earth element. 
   
     
     
         21 . The payload of  claim 20  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. 
 
     
     
         22 . The payload of  claim 20  wherein the processor is configured to flag the AIS message as suspect when the reported vessel position is determined to be inaccurate. 
     
     
         23 . The payload of  claim 20  wherein the parameter is propagation delay, and the processor is configured to:
 determine a value of the propagation delay of the AIS signal from the vessel to the space vehicle; 
 determine an expected value of the 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; 
 and wherein the antenna is a very high frequency antenna and the communications payload is configured to travel in a low earth orbit, and wherein the processor is configured to use global position information for the space vehicle to determine the position of the space vehicle. 
 
     
     
         24 . The payload of  claim 23  wherein the processor is configured to flag the AIS message as suspect when the reported vessel position is determined to be inaccurate. 
     
     
         25 . The payload of  claim 23  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. 
     
     
         26 . The payload of  claim 23  wherein the processor is configured to determine a frequency offset from a nominal frequency and a time delay from a start of a communications timing slot to determine the propagation delay. 
     
     
         27 . 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 an actual value of a parameter of the signal from the vessel to the satellite;   determining an expected value of a parameter of the signal from the vessel to the satellite based on said vessel position included in said received AIS signal and the satellite position;   comparing the actual value of the parameter to the expected value of the parameter; and   determining the accuracy of the vessel position based on the comparison.   
     
     
         28 . The method of  claim 27  further comprising flagging the message as suspect when the position is determined as inaccurate. 
     
     
         29 . The method of  claim 27  wherein determining a position of the satellite includes receiving the position of the satellite. 
     
     
         30 . 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 an actual value of a parameter of the signal from the vessel to the satellite;   determining an expected value of the parameter of the signal from the vessel to the satellite based on said vessel position included in said received AIS signal and the satellite position;   comparing the actual value of the parameter to the expected value of the parameter; and   determining the accuracy of the vessel position based on the comparison.   
     
     
         31 . The method of  claim 30  further comprising flagging the message as suspect when the position is determined as inaccurate. 
     
     
         32 . The method of  claim 30  further comprising flagging the message as suspect when the difference between the actual value of the parameter and the expected value of the parameter exceeds a threshold. 
     
     
         33 . The method of  claim 30  wherein determining the actual value of the parameter includes measuring a frequency offset from a nominal frequency and a time delay from a start of a communications timing slot.