Position reported by satellite is not actual position

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JP B

• December 23, 2022 13:19

Hello,

At this moment and since a while my boat is docked in a marina at the exact same position. A week ago, I installed a new AIS able to send message 27.

After a while, I saw a sat report appearing close to my position (there is no terrestrial station here). I thought that it was not mine due to the position about 300m to the WSW. By examining the issue further, I found out that indeed it is my boat. How is it possible to have such a gross error in the position? Do you apply an offset for the sat reports for some reason?

I have also contacted the manufacturer to see if they have a clue to that.

MMSI: 269367000

Best regaards

Jean-Pierre Beer

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  JP B

  • December 23, 2022 15:09

  After further research, I realized that the accuracy of the position in message 27 is far lower than the position in message 18. This explains the difference in position.

  I would still like to have an explanation about how MT calculates the position from sat reports. Is there any mitigation of the inaccuracy? I can see that two noon position reports are absolutely identical.

  What if a message 18 report is also received by the sat system along with message 27? What is the method used to take care of the discrepancy?

   

  JPB

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