Synthetic Aids to Navigation in Great Lakes

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Synthetic Aids to Navigation in Great Lakes

Postby jimh » Sat Oct 17, 2015 4:36 pm

In February 2014 the United States Coast Guard (USCG) announced that it would begin to employ AIS Aid-to-Navigation (ATON) technology as a supplement to using actual physical aids to navigation such as buoys. (For more on the announcement see an earlier discussion in The Old Forum.) In recent LOCAL NOTICE TO MARINERS (LNM) editions from the USCG 9th District, the USCG announced that in late 2015 there would be several AIS ATONs implemented, as follows:

From http://www.navcen.uscg.gov/pdf/lnms/lnm09392015.pdf :

Straits of Mackinac - De Tour Passage to Waugoshance Point - Chart 14881
LNM: 30/15

The following aids to navigation have been turned on as Synthetic AIS ATON. Synthetic AIS ATON is a signal broadcasted from an AIS base station to coincide with [an] existing physical aid to navigation. During periods when the aids are decommissioned for the season as advertised in the light list these aids will become Virtual AIS ATON. Virtual AIS ATON is a signal broadcasted from an AIS base station that is electronically charted, but non-existent as a physical aid to navigation.

Mackinac Bridge Lighted Bell Buoy "1" (LLNR 12625)
Mackinac Bridge Lighted Gong Buoy "2" (LLNR 12630)
Mackinac Bridge Lighted Bell Buoy "3" (LLNR 12645)
Mackinac Bridge Lighted Gong Buoy "4" (LLNR 12650)


Using the fine resources of http://MARINETRAFFIC.COM you can see the four AIS ATONs showing up in the Straits of Mackinaw at the bridge:

http://www.marinetraffic.com/en/ais/hom ... .8/zoom:12

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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Sat Oct 17, 2015 4:52 pm

It will be interesting to see how various recreational chart plotters will react to these AIS transmissions from Aids to Navigation. Until recently, most AIS transmissions originated from vessels, and most recreational chart plotters were capable of displaying these AIS targets. AIS transmissions from ATONs are a new aspect of AIS, and I anticipate that not all chart plotters are going to be ready to show those targets.

Boaters in range of the virtual or synthetic ATONs at the Mackinac Straits may want to check their chart plotters for the appearance of those AIS targets. It will be interesting to see how various chart plotters respond.

I am also assuming that the AIS receivers used by recreational boaters will be able to handle the AIS ATON signals, too.

More AIS ATONs seem to be planned for the Great Lakes. As the winter shipping season approaches, and more physical aids to navigation are removed for the ice season, we should see more AIS ATONs in service. From http://www.navcen.uscg.gov/pdf/lnms/lnm09352015.pdf :

St. Mary's River - Chart 14884

The following aids to navigation are scheduled to become Synthetic AIS ATON beginning late summer 2015. Synthetic AIS ATON is a signal broadcasted from an AIS base station to coincide with and existing physical aid to navigation.

Cedar Point Lighted Buoy "24" (LLNR 14415)
Cedar Point Lighted Buoy "23" (LLNR 14410)
Pointe Aux Pins Channel Lighted Buoy "10" (LLNR 14340)
Pointe Aux Pins Channel Lighted Buoy "9" (LLNR 14337)
Brush Point Lighted Buoy "15" (LLNR 14365)
Little Rapids Cut Lighted Buoy "105" (LLNR 14155)
Little Rapids Cut Lighted Buoy "101" (LLNR 14130)

St. Mary's River - Chart 14883
LNM: 14/15
The following aids to navigation are scheduled to become Synthetic AIS ATON beginning late summer 2015. Synthetic AIS ATON is a signal broadcasted from an AIS base station to coincide with and existing physical aid to navigation.

Lake Nicolet Lighted Buoy "73" (LLNR 13430)
Lake Nicolet Lighted Buoy "72" (LLNR 13425)
Lake Nicolet Lighted Buoy "67" (LLNR 13400)
Lake Nicolet Lighted Buoy "66" (LLNR 13395)
West Neebish Lighted Buoy "46" (LLNR 13525)
West Neebish Lighted Buoy "40" (LLNR 13555)
West Neebish Lighted Buoy "39" (LLNR 13560)
West Neebish Lighted Buoy "12" (LLNR 13700)
West Neebish Lighted Buoy "11" (LLNR 13705)
Munuscong Channel Lighted Buoy "13" (LLNR 13090)

St. Mary's River - Chart 14882
The following aids to navigation are scheduled to become Synthetic AIS ATON beginning late summer 2015. Synthetic AIS ATON is a signal broadcasted from an AIS base station to coincide with and existing physical aid to navigation.

Point Aux Frenes Lighted Buoy "20" (LLNR 12965)
Munuscong Lake Lighted Buoy "26" (LLNR 13010)
Point Aux Frenes Lighted Buoy "23" (LLNR 12985)
Round Island Lighted Buoy "17" (LLNR 12945)

St. Mary's River - Chart 14882
LNM: 14/15

Lime Island Traffic Buoy (LLNR 12915) Make the seasonal lighted buoy an synthetic AIS ATON during the season and a virtual AIS ATON during periods the seasonal aid is decommissioned.

Synthetic AIS ATON is a signal broadcasted from an AIS base station to coincide with and existing physical aid to navigation. During periods when the aids are decommissioned for the season as advertised in the light list these aids will become Virtual AIS ATON. Virtual AIS ATON is a signal broadcasted from an AIS base station that is electronically charted, but non-existent as a physical aid to navigation.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby Hoosier » Sun Oct 18, 2015 10:38 am

This is dumb. How do you see a synthetic ATON? If you don't have an AIS receiver you're screwed. Lake Nicolet is particularly bad since it can go from 30-feet to 30-inches in a couple of boat lengths.
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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Sun Oct 18, 2015 1:13 pm

I believe that most of the AIS ATON signals are intended to supplement the physical ATON buoys during the winter shipping season. Not too many recreational boaters are underway after December 1 in the St. Marys River and Straits of Mackinac.

Not only will you need an AIS receiver to see the AIS ATON devices, you will also need a chart plotter that is aware of this type of AIS signal and willing to display it. Your basic $400 budget chart plotter out there now may not be able to show AIS ATON targets. This approach will have to ripple through the recreational marine electronics industry for a while until the typical recreational boat has enough gear aboard to receive and display these synthetic or virtual aids to navigation. The big ships already have all that capability, and they're the ones out navigating the Great Lakes in December and January.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby K Albus » Mon Oct 19, 2015 12:53 pm

Hoosier wrote:This is dumb. How do you see a synthetic ATON? If you don't have an AIS receiver you're screwed. Lake Nicolet is particularly bad since it can go from 30-feet to 30-inches in a couple of boat lengths.


David - the synthetic ATONs are better than nothing. When the actual physical buoys get pulled for the winter, the synthetic ATONs will remain available. Assuming you have a capable chart plotter, you should be able to use the synthetic ATONs to assist your navigation in an area where no physical buoys remain. How is that a bad thing?

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Re: Synthetic Aids to Navigation in Great Lakes

Postby Dutchman » Tue Oct 20, 2015 8:42 am

It is true that not everybody has an AIS receiver or transponder. I don't have one on my small boats. But any extra navigation aids are good.

As for David'r comment of going from 30' to 30" , that's why we use depth-sounders and not trust a chart based on medium data, especially in a river where the bottom constantly might change. My depth finder is my best aid on my Whaler--better than my compass as I always have the sun, stars, and eyes to guide me in the general direction, but I can't see underwater. If I would only use charts and AToN I would have run aground many times with all my boats.
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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Wed Oct 21, 2015 12:24 pm

At the moment the only Synthetic or Virtual AIS ATONs I can find are the four marking the center passage under the Mackinac Bridge. For recreational boats those AIS ATONs have very little utility. Most of us can find the center span of the enormous suspension bridge and navigate between the two towers without much help. The vertical draft is not a concern, as most recreational boats do not need to pass under the center of the center span to get the 150-foot clearance. Water draft is not a concern as there is plenty of deep water there. There really is no utility for those AIS ATONs for a small boat.

I think the technology is interesting, and it could be of use in other situations. For example, if a ATON is off-station. The virtual or synthetic AIS ATON could indicate the proper location. Or an aid that has been damaged and sank--same idea.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Sat Oct 24, 2015 2:21 pm

A repeat of my earlier question: Does your chart plotter display synthetic or virtual ATONs created by AIS transmissions?

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Re: Synthetic Aids to Navigation in Great Lakes

Postby Hoosier » Sun Oct 25, 2015 9:44 am

Jim, Doesn't the boat's VHF radio have to be capable of receiving the AIS signal before the MFD can display it. And doesn't the radio need a network connection to the MFD. My Lowrance Link 8 has a whole menu section for AIS but my Standard Horizon, a generation older, doesn't.
1978 Outrage V20 with 2004 Suzuki DF-115. 1992 23 Walkaround with two 2010 Yamaha F-150s.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby Hoosier » Sun Oct 25, 2015 11:39 am

To clarify my previous post. It's looking like modern mid-range VHF radios are coming with a built-in AIS receiver, so you generally won't need to get a separate AIS receiver. The same is true, at least in the Lowrance line, with their mid to high range MFDs. My Elite-7 Chirp from last year has AIS display capability. I personally think AIS is more than "nice to have" if you boat in waters with a lot of commercial shipping, it's a "synthetic" radar.
1978 Outrage V20 with 2004 Suzuki DF-115. 1992 23 Walkaround with two 2010 Yamaha F-150s.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Tue Oct 27, 2015 9:44 pm

My concern is for the chart plotter display of AIS data from an Aid to Navigation (AIS ATON). Most of the chart plotters out today are really intended to show other VESSELS on their AIS display. I suspect they may not be ready to show AIS AtoN targets.

I would like to get some reports from users of various chart plotters regarding whether or not the AIS ATON targets show up. One of my favorite electronic chart plotters does not show AIS AtoN targets at its present software revision. The manufacturer is working on adding that capability.

I would not assume that just because a chart plotter can show an AIS target from a VESSEL that it will also be just as likely to show an AIS target from an Aid to Navigation. The AIS ATON sends a different message. The chart plotter has to know how to handle that specific message and how to display it. There are conventions that should be followed about the appearance on the chart plotter of the Aid to Navigation symbols, shapes, colors, and so on. Someone in range of the Mackinac Bridge should check their chart plotter to see if the synthetic AIS ATON targets are showing up.

Also, you do not have to be at the Mackinac Bridge to get the radio signals containing the AIS information. I suspect that the AIS signal for those synthetic AtoN targets is originating from an AIS BASE STATION that is nearby. Anywhere in the coverage area of that AIS BASE STATION, which is typically a radio of at least 20-miles and often more like 40-miles, you should be able to receive the AIS signals containing the AtoN message that should cause your chart plotter to display the synthetic Aid to Navigation.

For the synthetic Aids to Navigation at the Mackinac Bridge, I suspect that the actual radio signal originates from RFF BLISS, a Rescue 21 facility to the west of the Straits of Mackinaw. Compare at

http://navcen.uscg.gov/images/marcomms/ ... tMarie.jpg

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Re: Synthetic Aids to Navigation in Great Lakes

Postby Hoosier » Wed Oct 28, 2015 9:20 am

My Lowrance Link 8 radio shows AIS targets on its display screen. It shows all the usual AIS identifiers and does the CPA calculations internally, and has alarms that can be turned ON/OFF. In this case what des it send to the MFD other than the target icon and ID with location? It looks like the radio is doing all the math, not the MFD.

An aside: In the linked radio coverage graphic it's interesting to see that Isle Royale National Park is not in any station's footprint.
1978 Outrage V20 with 2004 Suzuki DF-115. 1992 23 Walkaround with two 2010 Yamaha F-150s.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Wed Oct 28, 2015 9:24 am

Yes, but the whole point is to know if your display shows targets other than VESSELS.

For example, does your display show AIS BASE STATIONS? Does it show AIS Aids to Navigation?

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Re: Synthetic Aids to Navigation in Great Lakes

Postby Hoosier » Wed Oct 28, 2015 11:31 am

I won't know till next Spring when I get the boat back in the water. It's stored in a metal barn so I can't try to get the Detour base station.

The premise for this thread is that the AIS AtONs are restricted to the Great Lakes. I'd say "for now". This could be a pilot program for the eventual roll out of AIS AtON capability everywhere. It makes sense to be able to go on the air after severe weather events where a bunch of physical AtONs have been lost. Once the AtONs have been programmed it's easy to activate them by base station coverage area.
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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Wed Oct 28, 2015 5:04 pm

The use of AIS synthetic or virtual aids to navigation is not restricted to the Great Lakes, and, in fact, that is probably the opposite. AIS ATON devices have been in the process of being deployed at many coastal areas, and the are just now coming to the Great Lakes. The use of an AIS ATON at the Mackinac Bridge has renewed my interest in them because now there is actually a chance for me to receive a signal from an AIS ATON. If not for the four devices at the bridge, I would have to travel to the Atlantic or Pacific coast to find an AIS ATON in operation.

The rollout of AIS ATON devices by the USCG was announced in February 2014, and the program will be two years old this coming February (2016).

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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Wed Oct 28, 2015 8:20 pm

The USCG Local Notice to Mariners (LNM) was just sent today. It announced many more conversions to Synthetic AIS AtoNs or Virtual AIS AtoNs, including many aids in my local area, the Detroit River, Lake St. Clair, and Lake Erie. Here is an excerpt from the LNM:

ATON DECOMMISSIONING

Lake Erie - Toledo Harbor - Chart 14847
Detroit River - East Outer Channel - Chart 14830
Detroit River - Chart 14848


Army, Detroit District Corps of Engineers P. O. Box 1027, Detroit, MI 48231, (313) 226-6443.
Additional information can be found on the U.S. Army Corps of Engineers Information Center website at

http://www.lre.usace.army.Mil/Missions/ ... recast.asp

Due to major maintenance of one of the Ninth Coast Guard District buoy tenders making it unavailable for buoy decommissioning, and the need to remove seasonal buoys prior to ice. The following seasonal lighted buoys will be decommissioned for the season earlier than their advertised light list dates. Several of these aids will be either synthetic or virtual AIS ATON as noted beginning 01 December 2015.

The following lighted buoys will be decommissioned for the season between 04-07 December 2015:

Maumee Bay Entrance Lighted Buoy “1” (LLNR 6045) Virtual AIS ATON
Maumee Bay Lighted Buoy “5” (LLNR 6065)
Maumee Bay Lighted Buoy “6” (LLNR 6070)
Maumee Bay Lighted Buoy “10” (LLNR 6090) Virtual AIS ATON
Maumee Bay Lighted Buoy “13” (LLNR 6115)
Maumee Bay Lighted Buoy “14” (LLNR 6120)
Maumee Bay Lighted Buoy “17” (LLNR 6135)
Maumee Bay Lighted Buoy “18” (LLNR 6140)
Maumee Bay Lighted Buoy “21” (LLNR 6155) Virtual AIS ATON
Maumee Bay Lighted Buoy “25” (LLNR 6170)
Maumee Bay Lighted Buoy “26” (LLNR 6175)
Maumee Bay Lighted Buoy “30” (LLNR 6195) Virtual AIS ATON
Maumee Bay Lighted Buoy “33” (LLNR 6210)
Maumee Bay Lighted Buoy “34” (LLNR 6215)
Monroe Harbor Lighted Buoy “1” (LLNR 6570) Synthetic AIS ATON
Monroe Harbor Lighted Buoy “2” (LLNR 6575) Synthetic AIS ATON
West Outer Lighted Buoy “1W” (LLNR 7365)

The following lighted buoys will be decommissioned for the season between 09-12 December 2015:

East Outer Lighted Buoy “2” (LLNR 6900)
East Outer Lighted Buoy “3” (LLNR 6905)
East Outer Lighted Buoy “5” (LLNR 6910)
East Outer Lighted Buoy “6” (LLNR 6915)
East Outer Lighted Buoy “7” (LLNR 6920)
East Outer Lighted Buoy “8” (LLNR 6925)
East Outer Lighted Buoy “9” (LLNR 6930)
East Outer Lighted Buoy “11” (LLNR 6940)
East Outer Lighted Buoy “12” (LLNR 6945)
East Outer Lighted Buoy “13” (LLNR 6950)
East Outer Lighted Buoy “14” (LLNR 6955)
East Outer Lighted Buoy “16” (LLNR 6960) Synthetic AIS
Amherstburg Channel Lighted Buoy “23” (LLNR 6965) Synthetic AIS

The following lighted buoys will be decommissioned for the season between 13-17 December 2015:

Ballards Reef Channel Lighted Buoy “81” (LLNR 7210)
Ballards Reef Channel Lighted Buoy “85” (LLNR 7225)
Ballards Reef Channel Lighted Buoy “86” (LLNR 7230)
Ballards Reef Channel Lighted Buoy “87” (LLNR 7235)
Mamajuda Shoal Junction Lighted Buoy (LLNR 7740)
Fighting Island Channel Lighted Buoy “90” (LLNR 7760)
Fighting Island Channel Lighted Buoy “91” (LLNR 7765)
Fighting Island Channel Lighted Buoy “91” (LLNR 7805)
Wyandotte Channel Lighted Buoy “25” (LLNR 7920)
Wyandotte Channel North Junction Lighted Buoy (LLNR 7925)
Belle Isle Lower Junction Lighted Buoy (LLNR 8205) Synthetic AIS ATON
Livingston Memorial Lighted Buoy “111” (LLNR 8220)
Belle Isle Upper Junction Lighted Buoy (LLNR 8230)
Belle Isle North Lighted Buoy “113” (LLNR 8245) Synthetic AIS ATON
Peche Island Lighted Buoy “114” (LLNR 8255) Synthetic AIS ATON

The following lighted buoys will be decommissioned for the season between 13-17 December 2015:

Lake St. Clair Lighted Buoy “2” (LLNR 8420) Synthetic AIS ATON
Lake St. Clair Lighted Buoy “8” (LLNR 8450) Synthetic AIS ATON
Lake St. Clair Lighted Buoy “13” (LLNR 8475)
Lake St. Clair Lighted Buoy “17” (LLNR 8495)
Lake St. Clair Lighted Buoy “18” (LLNR 8500)


SOURCE: http://www.navcen.uscg.gov/pdf/lnms/lnm09432015.pdf

This is very interesting news for me because it will put my AIS receiver in range of many AIS AtoNs, and that will give me a chance to see how my chart plotter responds to the AIS messages being sent. I will report my findings.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby Hoosier » Thu Oct 29, 2015 7:54 pm

The main point in the thread: can the current AIS receivers recognize the new synthetic AIS navigation aids?

My Link-8 can receive AIS from ships, shore stations, and navigation aids equipped with transponders. This is a whole new category since the navigation aid is being synthesized by the base station. There has to be some unique code that tells the user that what’s being displayed is a synthetic ATON, if it doesn’t it will create a lot of confusion when a boater goes looking for the aid and then thinks he’s lost because he can’t get a visual contact on it.

I asked Navico about this--TBD.
1978 Outrage V20 with 2004 Suzuki DF-115. 1992 23 Walkaround with two 2010 Yamaha F-150s.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Fri Oct 30, 2015 9:03 am

Regarding how an AIS Aid to Navigation should be displayed, there are recommendations for the appearance of the icon or graphic representation of such an aid to navigation for display on an electronic chart plotter. For more information, see

SYMBOLS FOR AIS ATON
http://www.nauticalcharts.noaa.gov/mcd/ ... _aton.html

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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Fri Oct 30, 2015 9:04 am

Regarding a radio receiver that tunes to the AIS frequencies: the receiver is already quite neutral about where the stations that send the signals are located. It doesn't care. It is just a radio receiver, and it will receive a signal from a land-based station sending AIS ATON data just as well as it will receive a signal from a ship. As long as the transmitter is in range, the AIS receiver will be receiving the signal.

The AIS radio receiver picks up AIS radio messages, and converts them to a data output to a chart plotter. I am fairly certain the AIS receiver does not really care about the message content. It demodulates the radio signal into a data message, and sends the message contents to the chart plotter. To make an analogy to other types of radio receivers demodulating received signals, an AIS receiver is like the radio in your car. It doesn't care if it is tuned to a country station or a rock station, it still demodulates the radio signal and sends it to a speaker for listening. So I do not anticipate any problems with AIS receivers working with AIS ATONs.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Fri Oct 30, 2015 9:12 am

I think the most likely problem for recreational boaters with an AIS Aid to Navigation (AIS ATON) will occur in their chart plotters. The chart plotter must be ready to receive AIS MESSAGE ID 21 (AIS AIDS TO NAVIGATION REPORT).

AIS Message 21 is a complex message. For details see

http://www.navcen.uscg.gov/?pageName=AISMessage21

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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Sat Nov 07, 2015 6:30 am

I notice that in Lake Michigan there is a new AIS synthetic ATON signal from the PORTS DES MORTS Entrance lighted bell buoy, located east of the Door Peninsula in Wisconsin. This AIS ATON is MMSI 993672158 and is probably being transmitted by AIS Base Station 3669779 north of Sister Bay, Wisconsin.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby Peter » Sun Nov 08, 2015 10:55 am

I'm struggling a bit with the concept of the usefulness of the virtual/synthetic AToNs and AIS for users that do not have a navigation system with RADAR or RADAR overlay. Allow me to explain a bit further...

The chart plotter shows representations of AToNs on the chart and as you move towards an AToN you will pass these representations on the chart whether they are really physically there or not. Really no different than a waypoint put on the chart except that this is a waypoint embedded in the chart. So I don't really need the the physical AToN if I were to rely only on the chart plotter and have faith that it is accurate. However, what I find is that the physical AToNs, when you pass by them and see them on the chart at the same time, provide mental confirmation that the chart plotter is working properly. (I used to do this with GPS navigation long before they had charts). Now one further step that I use for confirmation that the chart plotter is working properly is RADAR overlay on the chart. RADAR will light up physical AToNs and with an overlay function, they get put on the chart approximately where the representation of the AToN appears on the chart. You can see that in the image below. The radar is putting a blob of orange near the representation of green can "9" on the chart.

Image

Now if this is winter and they removed the physical AToN "9", my RADAR system would no longer paint an orange blob next to the representation of AToN "9" green can. So I'm no longer able to get RADAR confirmation that the chart plotter is working properly. Also, because AToN "9" green can has been removed, it's not there and so I can't get a visual confirmation that my chart plotter is working properly.

Now if I have AIS also overlaid onto the chart and there is a virtual AIS AToN signal representing physical AToN "9" green can, then in theory I would see that overlaid more or less on the chart plotter where the chart's representation of physical AToN "9" green can is on the chart. Now I have an electronic confirmation and if I assume that is accurate, all is "virtually" OK.

In short, I think this system is intended for those commercial vessels that should almost always have a RADAR system which they use as one of the several tools in the navigation aids tool box.
Last edited by Peter on Mon Nov 09, 2015 2:42 pm, edited 1 time in total.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Mon Nov 09, 2015 12:01 pm

Describing an AIS ATON as a waypoint is a good analogy. The Coast Guard is putting important navigation waypoints onto everyone's chart plotter--well, everyone with an AIS receiver and a chart plotter that can display the AIS ATON markers properly. I am awaiting the operation of several AIS ATONs in the Detroit River because they will allow me to test my chart plotter. I have some doubt about how my recreational-grade, several-years-old chart plotter will respond.

UPDATE: My older Lowrance first-generation HDS chart plotter was able to show AIS ATON targets. I write about this finding in a separate thread.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby Peter » Mon Nov 09, 2015 2:55 pm

Yes. When you receive the AToN AIS signal, effectively they are just causing your chart plotter to display a way point. That way point is not stored in your way point register. The only difference between this virtual AIS AToN and the AIS data from a vessel is that the vessel is taking GPS readings regarding its current position (and other data) and transmitting that data to you. The AToN AIS base station is simply broadcasting a fixed GPS position that is not where the base station is. They are fudging the lat/lon numbers in the AIS transmission to make the virtual AToN appear on your chart where they want it to appear on your chart. Think of it this way, if you had your chart plotter in simulation mode and were broadcasting AIS position data from that (assuming one can actually do this), the AIS information about your vessel would appear on a receiving chart that your vessel was in a particular location that you may have set, fixed or perhaps moving, when in fact it was not.

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Re: Synthetic Aids to Navigation in Great Lakes

Postby jimh » Wed Dec 02, 2015 1:30 pm

As the Coast Guard is removing buoys for the winter, they are adding Virtual AIS duplicates of them. I just noticed on MARINETRAFFIC.COM that between Port Huron and Lake Erie on the St. Clair River, Lake St. Clair, and the Detroit River there are now about twenty new AIS Virtual AtoN signals being broadcast.

I have been waiting for an AIS AtoN to be in range of my receiver and chart plotter. I will have to go mobile with my AIS receiver and chart plotter in my car to see how my older Lowrance HDS will display these signals. When I get some results, I will post them.