Methods and systems for consistency checking and anomaly detection in automatic identification system signal data
Methods and systems for validating positions reported in AIS message signals by fitting suitably chosen functions to signal characteristic data, such as timing and Doppler shift data, derived from a plurality of AIS message signals. Ships whose reported positions deviate from the fitted function may be flagged as suspect.
1. A method for detecting anomalous Automatic Identification System (AIS) message signals in a plurality of AIS message signals received by at least one satellite in space, the method comprising:
identifying a plurality of message characteristics associated with the plurality of AIS message signals;
fitting one or more group characterization criteria to the plurality of message characteristics of the plurality of AIS message signals; and
generating a computed message characteristic for a selected message signal based on the one or more group characterization criteria;
detecting whether a received message characteristic associated with the selected message signal conforms to the computed message characteristic within a predetermined tolerance.
2. The method of claim 1 , wherein the selected message signal is in the plurality of AIS message signals.
3. The method of claim 1 or claim 2 , wherein the one or more group characterization criteria comprise at least one computational function.
4. The method of claim 3 , wherein the fitting comprises determining the at least one computational function to be used when fitting to the plurality of message characteristics.
5. The method of claim 4 ; wherein the at least one computational function comprises a linear combination of spherical harmonics.
6. The method of any one of claims 1 to 5 , further comprising:
identifying a plurality of AIS message signals from a selected AIS transmitter in the plurality of AIS message signals;
determining at least one transmitter characteristic based on the plurality of AIS message signals from the selected AIS transmitter; and
using the at least one transmitter characteristic to refine the estimates of other message characteristics associated with the selected AIS transmitter.
7. The method of claim 6 , wherein the at least one transmitter characteristic comprises a transmitter timing offset.
8. The method of claim 6 or claim 7 , wherein the at least one transmitter characteristic comprises a frequency offset.
9. The method of any one of claims 1 to 8 , wherein the computed message characteristic comprises Doppler shift.
10. The method of any one of claims 1 to 8 , wherein the computed message characteristic comprises propagation delay.
11. The method of any one of claims 1 to 8 , wherein the computed message characteristic comprises a position of the AIS transmitter.
12. The method of any one of claims 1 to 11 , wherein the computed message characteristic comprises at least one characteristic selecting from the group consisting of: amplitude of the message signal and polarization of the message signal.
13. An apparatus for detecting anomalous Automatic Identification System (AIS) message signals in a plurality of AIS message signals received by at least one satellite in space, the apparatus comprising:
a memory, the memory storing the plurality of AIS message signals;
a processor, the processor configured to:
identify a plurality of message characteristics associated with the plurality of AIS message signals;
fit one or more group characterization criteria to the plurality of message characteristics of the plurality of AIS message signals; and
generate a computed message characteristic for a selected message signal based on the one or more group characterization criteria;
detect whether a received message characteristic associated with the selected message signal conforms to the computed message characteristic within a predetermined tolerance.
14. The apparatus of claim 13 , wherein the selected message signal is in the plurality of AIS message signals.
15. The apparatus of claim 13 or claim 14 , wherein the one or more group characterization criteria comprise at least one computational function.
16. The apparatus of claim 15 , wherein fitting the one or more group characterization criteria comprises determining the at least one computational function to be used when fitting to the plurality of message characteristics.
17. The apparatus of claim 16 ; wherein the at least one computational function comprises a linear combination of spherical harmonics.
18. The apparatus of any one of claims 13 to 17 , wherein the processor is further configured to:
identify a plurality of AIS message signals from a selected AIS transmitter in the plurality of AIS message signals;
determine at least one transmitter characteristic based on the plurality of AIS message signals from the selected AIS transmitter; and
use the at least one transmitter characteristic to refine the estimates of other message characteristics associated with the selected AIS transmitter.
19. The apparatus of claim 18 , wherein the at least one transmitter characteristic comprises a transmitter timing offset.
20. The apparatus of claim 18 or claim 19 , wherein the at least one transmitter characteristic comprises a frequency offset.
21. The apparatus of any one of claims 13 to 20 , wherein the computed message characteristic comprises Doppler shift.
22. The apparatus of any one of claims 13 to 20 , wherein the computed message characteristic comprises propagation delay.
23. The apparatus of any one of claims 13 to 20 , wherein the computed message characteristic comprises a position of the AIS transmitter.
24. The apparatus of any one of claims 13 to 23 , wherein the computed message characteristic comprises at least one characteristic selecting from the group consisting of: amplitude of the message signal and polarization of the message signal.