Abby's AIS Range ?

[SvenG]

In her most recent blog entry ( Abby's Blog )Abby Sunderland states

I just saw it on my AIS and it was 86 miles away

That seems like a very long distance (twice the nominal maximum) unless her's is satellite augmented ?

Did she read the AIS wrong or am I mistaken about the range capabilities or is there something else that I'm overlooking ?




-Sven

[Hampus]

Under extreme conditions it's possible, but not likely.

/Hampus

[Paul Elliott]

It's not that uncommon to receive AIS signals on the water at this range -- it happens quite often in my experience. It is definitely not something you want to depend on though. 10-20 miles is the norm. It depends on the weather.

[Jmolan]

This happens, we call them phantom hits. They are intermittent. Height of antennea is a big factor, and then a mtn. range can make a big difference. We have a "bowl" of a mtn. range in Alaska. When we are sailing by the bowl. we get 50 to 100 mile hits on ships.

[bewitched]

AIS is broadcast on VHF and like VHF Radio, the distance the radio waves travel is heavily dependant on atmospherics.

I regularly have AIS hits over 100nm.

[SvenG]

We are about to install the AIS which we just got programmed. It is interesting to know that it is actually possible to get hits from that far away when everything is right.


-Sven

[Paul Elliott]

From my home AIS receiver, elevation 1000 ft and a few miles from the ocean, I regularly receive AIS signals 1000 NM away, and occasionally as far as 2000 NM. These are solid signals, too, while they last. This is due to "tropospheric ducting", where the discontinuities in the atmospheric layers act as waveguides.

From the boat, with the antenna about 40 ft (the upper spreader) 100 NM is the maximum range seen so far.