202312 - SART detection reduced when search Radar on AUTO mode

During a recent marine search and rescue incident, a survivor was drifting in the water holding an activated 9 GHz (X-band radar) Search and Rescue Transponder (SART).

As edited from USCG (USA) Marine Safety Alert 12-22

The survivor saw four vessels pass close by as he held the SART above water, but none of the vessels’ crews detected the SART on their radars.

The survivor was finally rescued after three hours in tropical stormlike conditions. After the incident, the survivor’s SART was tested. It was found to be in good condition and operating in accordance with all requirements for a 9 GHz SART. So, what went wrong?

The post-incident analysis revealed the X-band radar settings that are optimal for navigation might actually prevent the SART signature from displaying on a searching vessel’s radar screen. The gain, sea clutter, rain clutter, and tuning on X-band radars are commonly operated in Auto mode, but this was found to drastically reduce or completely eliminate the ability of the receiving radar to display the dots or circular lines that indicate the SART’s position.

In addition, the orientation of the SART antenna and the height of the SART above the water both affect the ability of an X-band radar to detect a SART. The SART is designed to free-float or to be mounted on a pole in a life raft or on a survival craft. This height above the water will improve the device’s ability to transmit and receive signals, while also providing a much better target than a SART floating in the water.

The narrow end of a SART is the antenna. This should be vertical and as high as possible. But the narrow end is also the only suitable location for a person in distress to firmly hold a SART. If a person in the water holds a SART by its antenna, the SART’s ability to transmit and receive signals from an X-band radar will be reduced.

Lessons learned
 

• If you are on a vessel that has been assigned search and rescue duties and are searching for possible survivors, do not use the AUTO mode for radar rain, sea and gain settings. Use the manual modes and adjust the rain and sea clutter settings to the lowest possible setting that will still give a somewhat clear screen. The gain should be put to the highest possible adjustment without causing undue radar returns that pollute the screen.
• If you are a survivor floating in the sea and have an activated SART in hand, hold it as high as possible above your head but do not use the narrow end as a handle. This is the antenna.
• If you are a survivor in a lifeboat or liferaft, mount the SART as high as possible with the narrow end up