The United States Coast Guard (USCG) has begun to use the Automatic Identification System to send electronic Aids to Navigation (AIS AtoN) to supplement the physical buoys in the Great Lakes. Just recently, the USCG began transmitting AIS messages sending Message 21 for AIS AtoN navigation aids. I was curious if I could receive these AIS signals on my em-trak R100 AIS receiver, connect the NMEA-0183 data output of the AIS receiver to my Lowrance HDS-8 chart plotter, and observe how these electronic buoys were represented on the electronic chart display of the HDS-8.
Receiving the AIS AtoN signals in my region was not a problem. They are being sent from an N-AIS base station co-located at RESCUE 21 site RFF WAYNE, about 18-miles away from me, originating from a very tall (about 300-feet high) tower. The AIS signals were easily received at my location on an indoor antenna.
My HDS-8 chart plotter is a first-generation device. There has not been any firmware update for it from Lowrance since Februay 2012, almost four years ago. I was skeptical the HDS-8 would have the capability to show AIS AtoN icons because, at the time of the last firmware update, there were practically no such devices in use in the USA. I was very pleasantly surprised to find that my first-generation Lowrance HDS-8 was quite capable of displaying AIS AtoN targets. I demonstrate its capabilities with several screen captures.
HDS-8 presentation of AIS AtoN targets.
In the above screen capture, 15 AIS AtoN aids to navigation are shown. Not shown are about five more AIS AtoN marks in the lower Detroit River and Lake Erie. The targets in Lake Huron are over 50-miles from my receiver, but the actual signals for them are originating from the much closer tower at RFF WAYNE.
Having crossed the hurdle of receiving the AIS AtoN signals and seeing them on the chart plotter, the iconic representation of the aid to navigation was the next area of interest. As shown above, the aids are represented by a black rhombus with an internal black crosshair mark. Guidance for how AIS AtoN targets ought to be shown on electronic chart plotters is given by IEC Recommendation 68822. The basic AIS AtoN symbol is a diamond or rhombus shape with a black crosshair in the center, drawn with thin solid black lines. The applicable text from the recommendation says:
Real or synthetic AIS aids to navigation
(AtoN) shall be presented as a diamond with
crossed lines centred at the reported position
of the AtoN. The crossed lines shall be not
more than 2 mm in length and the sides of
the diamond shall be not more than 6 mm in
The diamond and crossed lines shall be
drawn using a thin solid line style.
The symbol representations for a real or synthetic AIS AtoN should look like this:
Recommended symbols for Real or Synthetic AIS AtoN
Before we can assess the Lowrance HDS-8 display and its compliance with recommendations, we must first identify the type of AIS AtoN that is being received.
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