Realities of S-AIS
How AIS is Used, Myths about AIS, the Quality and Timeliness of AIS data, and the Future of AIS for Maritime Domain Awareness.

Illegal fishing, piracy, inadvertent nature preserve trespass, and damage to ships are some of the most discussed topics for shipping and maritime industry experts.  To tackle these issues, better and more accurate monitoring of vessels is of critical importance. The Automatic Identification Systems (AIS) transmit information about vessels' identity and location and provide a source for much needed, more accurate insight into marine traffic. But what exactly is AIS and how can we benefit from it?

Terrestrial versus Satellite AIS

To kick off our discussions, let's explore the differences between these two systems. Most Satellite-AIS (S-AIS) data providers will include a coastal feed as part of their overall service. As valuable as this is, it can create misleading quality metrics. A receiver collects coastal (terrestrial) data, usually mounted on a tower near ports. These receivers are inexpensive, and thousands have been distributed around the world. Nations, companies, and individuals deploy receivers, and there are no restrictions on their use. Many companies have networks of individuals who place a receiver at their homes with a view of the sea and integrate the data received into a global view.

The range of coastal receivers is controlled by three factors:

  1. the height of the antenna,

  2. the presence of any blockage (mountains, buildings, etc.), and

  3. the quality of the installation, including the degradation caused by exposure to the elements over time as well as the quality of equipment, cables, and initial installation.

As you can imagine, the quality of the received data ranges from very high to very poor. With a good quality installation and an antenna height of around 100 feet (30m) where it can see the ocean, the receiver has a line of sight of about 12 miles to the horizon. AIS uses the VHF frequency, which bends around the earth's curve to some degree, and therefore the effective range is approximately 30 to 50 miles. Ships can be seen at 70 miles or more in some instances, but detection becomes intermittent and unreliable at long ranges.

Uses of AIS Data

Satellite AIS, combined with Coastal AIS data, provides analysts with the ability to track ships globally or within any area of interest.

Many uses of S-AIS have emerged over time. The list below shows a summary of the major uses of ship-tracking data today:

  • Fleet monitoring and management

  • Collision avoidance

  • Maritime security

  • Accident investigation, search and rescue

  • Improving shipping/routing strategies

  • Fleet performance analysis

  • Ship emissions estimation

  • Trade flows in real-time 

One key issue is, for each application, to understand the importance of accuracy and timeliness of the data. For many applications, it matters whether the position information and the decision support data derived from positions are correct when decisions are made.

When using AIS or S-AIS, users are rarely interested in all ships everywhere. Instead, there are Areas of Interest (AoI's) and Vessels of Interest (VoI's). Times of Interest (ToI) should also be considered as elements. With Satellite AIS marine traffic, ships are detected intermittently, regardless of the number of satellites involved. Intermittent detection occurs even with coastal AIS networks whenever ships are beyond 30 miles from the base station. This means that the AIS data about a ship is always old and often obsolete.

If you are involved in any of the aforementioned applications, it is essential for you to understand the realities of the age of the data you are using for decision-making. Most data suppliers will provide the ability to see the time of the detection being presented. It is always included in data streams and API data access. Still, map presentations often require the user to click on a ship to display the message's age, and it is often displayed at the bottom of a long list of meta-data about the ship.


An analyst will sometimes misread a map that appears to show ship positions in an area and may make expensive decisions based on the presented data. For this reason, analytics can make a huge difference by removing the need for the analyst to make manual calculations.


Time Synchronization is Critical

For many applications, users must also predict the vessel tracking position into the future, estimate the estimated time of arrival (ETA), or plan to meet the vessel traffic at a particular time. For these uses, a thorough understanding of the time factors is essential. To maximize the value of satellite ais data, training for all analysts about how to interpret the data being presented is essential.

An analyst will sometimes misread a map that appears to show ship positions in an area and may make expensive decisions based on the presented data. For this reason, analytics can make a huge difference by removing the need for the analyst to make manual calculations.

A technology that provides a time-synchronized set of ship positions in any area is TimeCaster™, provided by Maerospace. Using patent-pending machine learning algorithms, TimeCaster™ provides an API or web view via the data stream. This approach has been proven to provide a global accuracy of fifteen times (15x) improvement overuse of raw marine traffic ais and Coastal data. Time-synchronized positions for all ships can be provided on a NowCast® basis (as of "now" and then the ship positions are updated every 10 minutes) or for the future for any set of ships or area of interest. FutureCast™ capabilities can provide this time-synchronized view for many hours or days into the future. In all cases, the analyst has access to the original ais traffic as well as the forecasts.

Monitoring and Alerting

Decision-making is about making things happen in the future. Whenever a decision is needed to support any of the use cases shown in the table above, the user must assess where the ship will be when the decision comes into play, whether it is planning to receive cargo, interdict a vessel position, direct a vessel position to a new port, or predict commodity prices based on short-term flows.

When the position predictions are made manually, the process becomes slow and subject to errors. With an automated monitoring and alerting system, such as Maerospace's ADVISOR® service, the analysts can focus their time and effort on the core problem they are trying to solve.

Check out TimeCaster

Ready to get near real-time vessel positions and predictions of up to 72 hours, ten times more accurate than other datasets?


About Maerospace

This blog shared what Maerospace has learned about the realities of global AIS and Satellite-AIS. Over the past decade, Maerospace team has worked with every satellite AIS supplier and with users and analysts from around the world. In their work to provide a vastly improved maritime domain awareness data feed using advanced analytics, they have developed a deep understanding of what goes on in the complex global network of sensors that support AIS. The goal of this article was to share what Maerospace has learned in hopes that this precious resource can continue to be enhanced. With a proper understanding of the AIS system, this unique global resource can be a critical tool to help save lives, guard the borders, protect the environment and enhance trade.

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May 2022
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