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Marine Electronics Journal Blog

From Twain to high-tech, Part 2


Tracking conditions on inland waterways

Last week we looked at the evolution in how pilots and crews tracked and communicated with each other about conditions on rivers from the days of Mark Twain until today. This week we check in on the central role played by modern marine electronics, namely Automatic Identification Systems (AIS) and Application-Specific Messages (ASM).We’re grateful to Brian Tetreault for writing the article for MEJ, from which this information is excerpted.


By Brian Tetreault

AIS is essentially a means of communicating digitally via VHF radio. Since AIS is mandated for carriage on certain vessels, AIS equipment needs to be tested to ensure it operates as required. The International Electrotechnical Commission (IEC) has published several performance standards used to test AIS equipment. IEC also publishes other standards that are referenced in the AIS standards such as those dealing with equipment used in the marine environment, networking and interface standards, and others. This highlights another benefit of standards—they can be reused as needed, reducing duplication of effort and reducing the overall workload on developers, while ensuring compatibility across different uses.

One of the advances that has come about in recent years is the ability for different shipboard equipment to be connected to each other. The benefits of this are readily apparent: it allows information from one piece of equipment to be used in another, such as AIS vessel information displayed on a radar to provide identification of otherwise nameless radar returns. In order for this to occur, the equipment must “speak” a common language. The NMEA 0183 Standard for Interfacing Marine Electronic Devices allows many different types of equipment to exchange information in a format that is universally understood.

 ASMs: Delivering more info

Finally, as the uses of AIS are explored and expanded, standards are being developed to ensure it is done in a deliberate way to maximize the benefit to all users. One of the abilities of AIS is to communicate information beyond the standard messages. This information can include weather observations, water levels, lock operational information, notices of impediments in the river, and other navigation information. The information uses messages that can be designed to convey specific information for use by applications separate from the AIS equipment. These are called “application-specific” messages, or ASMs. However, there were no standards guiding the creation of ASMs, other than some basic guidelines (provided by international standards-writing organizations).

In order to ensure international compatibility and reduce duplication of effort, the (US-based Radio Technical Commission for Maritime Services---RTCM) has drafted a standard entitled: “Creation and qualification of application-specific messages.” This standard provides requirements for creating and testing ASMs to ensure they are commonly understood, such as using common formats for time, standard units of measurement, ensuring compliance with message formatting requirements and other specifications to ensure the smooth operation of the AIS system as a whole. The screen shot at right shows an Inland Electronic Navigation Chart (commonly called an IENC) as displayed on a vessel’s Electronic Charting System, or ECS, with lock order information portrayed that was delivered via AIS ASM.


AIS: Still growing

Additional standards and guidelines are in development for other aspects of AIS, including management of transmission of AIS information, including ASMs, virtual aids to navigation, and managing message transmission to avoid overloading the AIS data link. It is anticipated that existing and new standards and guidelines will continue to evolve as use of this technology matures.

In summary, it is important to acknowledge that while advances in technology can provide immense benefits to navigation safety and efficiency, these advances cannot progress in a haphazard manner. Innovations need testing by providers of information, equipment manufacturers and users and incorporation into a framework of well-defined standards.

Quoting from Twain’s “Life on the Mississippi:”

“Imagine the benefits of so admirable a system in a piece of river twelve or thirteen hundred miles long, whose channel was shifting every day! The pilot who had formerly been obliged to put up with seeing a shoal place once or possibly twice a month, had a hundred sharp eyes to watch it for him, now, and bushels of intelligent brains to tell him how to run it. His information about it was seldom twenty-four hours old.”

The system Twain describes has not gone away—it has been enhanced through the deliberate application of technology to navigation through a framework of standards. Instead of a “hundred sharp eyes” the pilot now has the benefit of millions of pieces of information, gathered by thousands of persons and sensors, available immediately, most certainly less than 24 hours old. As technology advances it will continue to improve the quantity, quality and timeliness of information presented to waterway users.


About the author

Brian Tetreault is Navigation Systems Specialist at the US Army Corps of Engineers Research and Development Center.


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Comments | Leave a Comment
Page 1 of 2 ( 9 comments)

Darryl:(3/27/2017 10:17:15 PM) "Putting the MSRP with each unit reviewed would have been helpful. If each unit was actually tested, the reports on each unit would have been helpful too.

Thanks Darryl---we generally don't mention prices due to confusion over so many variations---MSRP (mfg. suggested retail price), MAP (min. advertised price), MRP (min. resale price) and then there are internet prices on some websites that go their own way. But your point is well taken--buyers need to know if something is in their price range. We'll work on it.
There is independent testing of some of these products on sites like but the information we receive from manufacturers rarely cites the results of any shootouts they may conduct against the competition's products. "
Laurie Seibert:(2/16/2017 2:00:20 AM) "Thanks EV Collier for sharing this informative blog. It is important to know the causes of EMI filters. We use these parts in our daily life in the electronic products so we should know that what are the causes are cures of EMI Filters.

Great job and keep updating!

Laurie Seibert"
Yes:(2/10/2017 7:22:40 AM) "EMI/RFI filter causes and cure. There are very few people who share such information with everyone. I was looking to read such informative blog!

Great job!

Lisa Wilson
hugo:(1/30/2016 2:00:32 AM) "Why is no integrated ais transceiver available? Only recivers.


Each AIS system consists of one VHF transmitter, two VHF TDMA receivers, one VHF DSC receiver, and standard marine electronic communications links (IEC 61162/NMEA 0183) to shipboard display and sensor systems (AIS Schematic). Position and timing information is normally derived from an integral or external global navigation satellite system (e.g. GPS) receiver, including a medium frequency differential GNSS receiver for precise position in coastal and inland waters. Other information broadcast by the AIS, if available, is electronically obtained from shipboard equipment through standard marine data connections. Heading information and course and speed over ground would normally be provided by all AIS-equipped ships. Other information, such as rate of turn, angle of heel, pitch and roll, and destination and ETA could also be provided. Check out:"
Islander Sailboat Info:(12/4/2015 9:49:32 AM) "Great post!! This is the missing introduction I've been looking for. Thank you for taking a complicated subject and making it very easy to understand."
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