AIS Phantom target

[Piddy]

Morning all,

Is it possible to have a phantom target on AIS?
When I was traveling back across the Channel last week, we had a persistent target about 2-3miles in front of us. I could see all the other close targets clearly but one that had a description of 49' pleasure boat (so surely big enough to see) traveling at 6knots in the same direction as us. We had excellent visibility all day (Thursday) and with very little wind, boats stood out very well.
This was for the whole trip from Alderney to the Needles. At no time did I see a boat of that size but it was a constant target on the screen.

Although I have had an AIS receiver for a few years, I haven't had to travel in fog before with the benefit. We now have an MFD with radar and AIS overlays. On the day we went from Cherbourg to St Peter Port, we had a small flotilla traveling on the same tide and once past Cap De la Hague, the vis reduced to no more than 300m (as measured with boats that close but unseen).
On the MFD, the AIS targets are big and bold but the non-AIS transmitters are much harder to spot on radar.
I've been using radar for at least 25 years so have some idea of how to get a good picture but now with the AIS overlay, it's so easy to relax thinking you know where everyone else is. This particular foggy trip reminded me to keep watching for echos as well as AIS even occasionally turning off the AIS overlay to see what else is around under the targets.

 

[RIBW]

..Is it possible to have a phantom target on AIS?
When I was traveling back across the Channel last week, we had a persistent target about 2-3miles in front of us. I could see all the other close targets clearly but one that had a description of 49' pleasure boat (so surely big enough to see) traveling at 6knots in the same direction as us. We had excellent visibility all day (Thursday) and with very little wind, boats stood out very well.
This was for the whole trip from Alderney to the Needles. At no time did I see a boat of that size but it was a constant target on the screen.

Did you happen to record its MMSI?
Someone woith the right access to one of the internet trackers (MarineTraffic?) may be able to look at its historical track.
Cheers
Bob

 

[PaulRainbow]

Vessel details are entered by the AIS installer, so it is possible that the target was a much smaller vessel, that you couldn't visually see.

 

[lw395]

49ft motor launch which didn't have a particularly high superstructure could be quite hard to see at 2-3 miles end on?
Or even a yacht with no sails up?

I can't see any means that this phantom target could be created, other than perhaps a test mode in the AIS receiver's firmware, or somebody deliberately choosing to transmit a spoof intended for your consumption?

 

[Piddy]

49ft motor launch which didn't have a particularly high superstructure could be quite hard to see at 2-3 miles end on?
Or even a yacht with no sails up?

I had quite a lot of time to spare during the day and spent a fair bit of it looking through binoculars - particularly when other boats were at that range so I had a reference but didn't see anything.
It wasn't just me - SWMBO was encouraged to look as well as she has much better eyesight than me but still, nothing was seen.

 

[roaringgirl]

Easily generated by something transmitting the wrong location

 

[Polly's Kettle]

Are you, by any chance, a 49 ft pleasure boat?!? Sounds like you have the setting switched on to show yourself.

I've had it before where as well as the black triangle (me), there was a pink triangle (AIS target) very close to me. Turned out it was me, and it was a setting. Can't remember for sure where the setting was, but I have a feeling it was a setting on the DSC radio, not the chartplotter. Took me ages to work it out.

Of course, you'd still have to ask why it was consistently 2 miles away. Mine was definitely offset, but not by much.

Edit:
Just in case it helps match to your situation, I have a Raymarine MFD, with a B&G radio.

 

[lw395]

I'm struggling to see any other explaination.
Short of seeing your own transmission with a 2-3mile offset in the position. Which can only be an error in the GPS coordinates?
Did any other vessels receive this signal?
Was there an MMSI number? Was the course and speed received and was it exactly the same as yours?
What happened at the end of the crossing? did it just disappear?
Were you following an autopilot track where it's credible someone else would be tracking that closely?
Did it slowly pull away/get closer/track your speed exactly?

What AIS kit do you have?
Were you by any chance going due North?

 

[Piddy]

I'm struggling to see any other explaination.
Short of seeing your own transmission with a 2-3mile offset in the position. Which can only be an error in the GPS coordinates?
Did any other vessels receive this signal?
Was there an MMSI number? Was the course and speed received and was it exactly the same as yours?
What happened at the end of the crossing? did it just disappear?
Were you following an autopilot track where it's credible someone else would be tracking that closely?
Did it slowly pull away/get closer/track your speed exactly?

What AIS kit do you have?
Were you by any chance going due North?

Def not me. Checked on Marine traffic by others monitoring us. I can't find the older tracks from that week n MT- perhaps because I have a free account.
No idea
There was but I didn't take a note or picture
We started sailing on a beautiful afternoon so lost interest in the display so have no idea what happened at the Needles
On auto pilot but not a track
It slowly got closer from 3.5miles to 2.8 on the same track - a big bulge to the East due to tides that day

Em-Trak B100 AIS A100 splitter
Raymarine C120 MFD & radar
Generic GPS for position
Yes.

 

[Polly's Kettle]

What radio are you using?

When you say others checked on marine traffic, do you mean they could see 2 boats - you and the phantom? If they could only see 1 boat, it rather supports the potential that it was you. It can be caused by confusion within your own system - a DSC radio, which has AIS capability, telling the MFD to plot yourself. No-one else would see it.

 

[RichardS]

Easily generated by something transmitting the wrong location

The target location is generated by the target's own GPS receiver so the target would have to have a defective GPS unit which applies a constant offset to the actual position. I'm sure that it's possible but it seems unlikely.

Richard

 

[Piddy]

What radio are you using?

Simrad RD68 radio - no AIS
The phantom boat had a name on the AIS info but it was a week ago and I now can't remember it. IIRC, it was a French boat but that's dragging info from deep in my memory bank so may be wrong.


When you say others checked on marine traffic, do you mean they could see 2 boats - you and the phantom? If they could only see 1 boat, it rather supports the potential that it was you. It can be caused by confusion within your own system - a DSC radio, which has AIS capability, telling the MFD to plot yourself. No-one else would see it.

Family tracked us across Channel - no one else looked at the phantom as far as I am aware....

 

[JohnGC]

Family tracked us across Channel - no one else looked at the phantom as far as I am aware....

Check your antenna offset setting (assuming there is one for your transmitter).

John

 

[LadyInBed]

49ft, I thought boat details were entered in metric units.
In the expand target details, did it show any more details than MMSI and Pleasure?

 

[GaryShaw]

Isn't the furthest distance possible to see at sea level 2.9 miles? Isn't it possible it was just outside the visible range of what you can see?

 

[MM5AHO]

I have experienced something similar. Last year on one of many trips round the Mull of Kintyre, heading east, saw 5 fishing boats in a tight group. Thinking that strange I headed towards their location, (between MoK and Sth Arran) to find none of them. I sailed right through their position. Good viz. If they were real I'd have seen them. Still can't explain that one.
Of course its possible to transmit false positions, that's how lighhouses and buoys are done.

 

[ShinyShoe]

Easily generated by something transmitting the wrong location

If AIS allowed an external GPS... Yes. But it's integrated by the rules.

I have experienced something similar. Last year on one of many trips round the Mull of Kintyre, heading east, saw 5 fishing boats in a tight group. Thinking that strange I headed towards their location, (between MoK and Sth Arran) to find none of them. I sailed right through their position. Good viz. If they were real I'd have seen them. Still can't explain that one.
Of course its possible to transmit false positions, that's how lighhouses and buoys are done.

Lighthouses etc do it using a purposefully designed unit. It's not something a standard AIS can do. Nor is it something a standard bodger / hacker can do.

Isn't the furthest distance possible to see at sea level 2.9 miles? Isn't it possible it was just outside the visible range of what you can see?

Yup.

And you are assuming it is 49ft (15m) rather than that being some default number ...

 

[Piddy]

49ft, I thought boat details were entered in metric units.
In the expand target details, did it show any more details than MMSI and Pleasure?

That's possibly because I have the units on my MFD set to feet.

It detailed GOG and SOG but I find the Raymarine AIS target data a bit lacking. When I fed it into Navi-Sailor on my laptop, I got a lot more info.

 

[Piddy]

Isn't the furthest distance possible to see at sea level 2.9 miles? Isn't it possible it was just outside the visible range of what you can see?

Nope targets up to 30 miles from a masthead ariel - may be not yachts but there were plenty of others around this target.

 

[Piddy]

I have experienced something similar. Last year on one of many trips round the Mull of Kintyre, heading east, saw 5 fishing boats in a tight group. Thinking that strange I headed towards their location, (between MoK and Sth Arran) to find none of them. I sailed right through their position. Good viz. If they were real I'd have seen them. Still can't explain that one.
Of course its possible to transmit false positions, that's how lighhouses and buoys are done.

Hopefully it's not just me then!