When we explain the functionalities of an AIS class B Transponder, we are often asked if that is the same as a radar transponder. The answer is clearly no. A radar transponder is an emergency device included in the internationally proposed GMDSS measures for search and rescue at sea, i.e., a radar transponder is used at critical situations, to detect radar targets at emergencies. This system is also called SART (Search And rescue Radar Transponder)
It works by answering to a radar eco signal. That is why it is sometimes called “responder”. When activated, it starts transmitting signals as soon as it detects one from a radar. It is expected to be mandatory in Spain since 2009.
Therefore, essential differences between a radar transponder and AIS, are:
- SART does not work on a regular basis, but only under emergency situations.
- SART does not identify ships, only sends a signal that lets a radar know that there is somebody out there.
- Therefore, SART does not let you tracking a fleet, and identifying them; it is only able to show unidentifiable targets with no extra information.
AIS has nevertheless it’s own emergency standard, proposed by IMO here. The proposal is the AIS-SART, not to be confused with the radar transponder, since it actually means: AIS Search And Rescue Transmitter. But we will write about this in future posts.