Vessel tracking from space with Satellite AIS

Posted by Dean Rosenberg

As many of the readers of this blog already know, Automatic Identification System (AIS) is a VHF protocol that has been mandated on large vessels by IMO for collision avoidance and to enhance navigation since 2005.  Every vessel over 300 gross tons (or over 65 feet in the USA) carries an AIS transponder that receives broadcasts from nearby vessels, and also transmits identifying information about the vessel carrying the transponder.  Information including a ship’s location, speed, and identifying information is transmitted multiple times per minute when a vessel is underway, and every few minutes when docked.  You can view all details associated with the AIS specification at the USCG Navigation Center website.

satellite ais resized 600       Photo credit: Institute of Aeronautical Technology

Once AIS became a global standard, the industry realized that in addition to leveraging the safety benefits of AIS in the wheelhouse, organizations could also drive significant value in their shore-side operations by using AIS to increase visibility and transparency to vessel movements around the world.  PortVision launched its web-based service in 2007, and has since expanded to provide global coverage with a network of AIS receivers around the world. 

The challenge with a shore-based AIS service is that an individual AIS receiver is limited to about a 50 mile radius.  Ship tracking through shore-based (also known as “terrestrial”) AIS requires that each vessel be within 50 miles of an AIS receiver in order to be tracked in the system. 

Terrestrial AIS provide significant value to users, including providing near-real-time vessel tracking when vessels are near shore.  However, once a ship is in open water, terrestrial AIS becomes less effective.  Initially, PortVision took steps to increase coverage of AIS network by adding receivers on offshore assets such as offshore platforms and workboats in high-density areas such as the Gulf of Mexico.  However, while expanding visibility in those areas, the offshore receivers still did not address the challenge of tracking ships at sea. 

In 2008, the first commercial AIS receivers were launched into orbit as a satellite payload.  The initial satellite launches were largely experimental, and demonstrated that it indeed was possible to detect AIS signals of vessels in open water from an orbiting satellite.  This kicked off the era of satellite AIS, as several commercial operators began offering satellite AIS services to both government and commercial clients.

From a wheelhouse perspective, satellite AIS provides minimal value.  However, from a shore-based business perspective, satellite AIS provides many benefits, including:

  • Ability to track any AIS-transmitting vessel globally
  • Ability to support search-and-rescue and anti-piracy measures by increasing the visibility of ships at sea by first responders and security personnel
  • Ability to provide market intelligence through aggregating data across many vessels and regions to answer business questions
  • Ability to support compliance and law enforcement activities


The above benefits are compelling.  However, it is also important to recognize the limitations of satellite AIS

  • Much lower reporting frequency.  While terrestrial AIS can report vessel positions in near-real-time (with multiple updates each minute), satellite AIS has significantly higher latency and lower frequency of reporting.  Current satellite AIS service providers typically provide position updates on specific vessels only a few times each day.  While this lower frequency of reporting still provides compelling value to track the progress of ships at sea, it does not allow for many of the advanced alerting and reporting features that are available with terrestrial AIS.
  • Limited detection of vessels.  The ability to detect AIS signals from space is currently an imperfect “art”.  Electromagnetic interference (particularly in dense areas) often limits the ability to detect vessels in congested areas, even when vessels are transmitting their AIS signal.
  • Cost.  It is expensive to launch a satellite, and the commercial satellite operators need to recoup that investment.  As such, satellite AIS typically carries significantly higher licensing fees than terrestrial-only AIS providers

PortVision has been providing satellite AIS to customers since the first satellites were launched over 5 years ago.  We continue to maintain a leadership position in aggregating terrestrial, offshore, and satellite AIS to provide the highest-value offering to our users.  Combined, we process over 50 million ship location reports per day from all AIS sources in our network.  And satellite AIS data plays an important role for many of our users, particularly those users who require in-transit visibility to ships around the world.

To learn more about PortVision's AIS vessel tracking, download our FREE PortVision 360 info sheet below.

Get My PortVision 360 Info Sheet

Posted on Jan 27, 2015, 2:01:00 PM

Topics: Blog