Ever wonder when you look out into the Santa Barbara channel what all those ships are doing out there? What port did they come from, where are they going, what cargo is aboard, how big they are, and what country are they from? Looking at the map above, each of these markers is a vessel being tracked and commonly known worldwide as the Automatic Identification System (AIS). This is an internationally mandated program for Identifying more than 10,000 commercially operated ships at any one time around the globe. An AIS transceiver aboard each vessel functions not only to identify the vessel but augments radar as a collision avoidance system. There are two classes of reporting known as Class A and Class B and operate in the VHF spectrum. This basically accommodates larger vessels and smaller vessels who need not report their position so often. Digitally the ships “talk” to each other giving their speed, heading and location.
SBARC operates two AIS passive receiver stations. Station 533, SBARC-SBA, which is located at our Mesa site at 470 ft and the second is Station 1360, SBARC-SYP, is located at Santa Ynez Peak at 4300 ft. Normally coastal marine traffic is tracked by AIS out to about 50 nautical miles. However, the contrast in elevations between our two passive receivers gives us a real picture of West Coast signal propagation. The ship placement of their AIS antenna can be anywhere from 20 to 75 ft above the water line on the ships structure. Given a transmit power of roughly 20 watts we may witness some unusual path characteristics. We are able to track some vessels out to 800-900 nautical miles, which is about 900-1000 statute miles. If you look at the station reports, the ducting phenomenon may be visually seen as plots on the map. It is not unusual to see ships beyond Baja California along the Mexican coastline.
Of what local importance is AIS? With each ship reporting its speed and position it makes the Channel Islands passage safer by requesting a speed reduction to accommodate the migrating whales and cross channel small boat traffic. In addition, the added advantage is lower emissions from the huge diesel engines which power the ships.
If you have young children who may at times become bored get them interested in a mini-science project by tracking ships over a short period of time. A simple matrix chart will work showing what flag they fly and the cargo they carry. See how many ships they can locate in 2-3 hours. They would learn a lot about geography, countries, commerce, navigation, and so much more. If you can see the ocean area a pair of binoculars will help locate a vessel and compare it with the screen display. You may see displays of AIS at the Santa Barbara Maritime Museum or come to the SBARC club station for a demo on how it all works.
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