2.6Locating a Ship or Survival Craft in Distress by SART
SART background
The SART is required on vessels of 300 GT and above by the 1974 SOLAS Convention as amended in 1988 (GMDSS). Performance stan- dard is specified in IMO Resolution A.697 (17).
SART activating conditions
The SART should operate correctly when inter- rogated at a distance of up to at least five miles by a navigational radar complying with resolu- tions A.477(XII) and A.422(VII) and IEC 936, with an antenna height of 15 meters. (It should also operate correctly when interrogated at a dis- tance of up to 30 miles by an airborne radar with at least 10 kW peak output power at a height of 3,000 feet.)
How SART works
Upon receiving a radar signal from a rescue party, the SART automatically transmits a series of twelve frequency sweeps at a frequency between 9200
Screen A: When SART is distant | Screen B: When SART is close | |
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The length of a SART mark depends on the radar’s receiver bandwidth and sensitivity. For the bandwidth of 12 MHz, the length is 45 meters approximately and for the bandwidth of 3 MHz (usually on the 6 mile range or larger), 12 meters approximately.
How to show SART marks on the display
Detune the radar receiver manually by turning the TUNE control out of best tuning condition. This erases or weakens all normal radar echoes; but, the SART marks are not erased because the SART response signal scans over all frequencies in the 9 GHz band. When the radar approaches the SART in operation, the SART marks will en- large to large arcs, blurring a large part of the screen. Reduce the sensitivity and adjust the sea clutter control of the radar.
Summary to detect SART responses
1)Use range scale of 6 or 12 nm as the spacing between the SART responses is about 0.6 nm (1125 m) to distinguish the SART
2)Turn off the automatic clutter suppression.
3)Turn off the Interference Rejector.
4)Turn off the Echo Average.
General remarks On receiving SART
Position of
SART
9500 MHz
9200 MHz
Radar antenna beamwidt h
SART mark length
Sweep time
7.5 µs
100 µs
Radar receiver bandwidth
1Radar range scale
When looking for a SART, it is preferable to use a range scale between 6 and 12 nautical miles. This is because the spacing between the SART responses is about 0.6 nautical miles (1125 m) and it is necessary to see a number of responses to distinguish the SART from other responses.
2SART range errors
There are inherent delays in the SART responses as the SART has a trigger delay and may also
Figure 2-8 Appearance of
SART marks on the radar display
have to sweep through the whole radar band be- fore reaching the frequency of the search radar. At medium ranges of about 6 nautical miles the range delay may be between about 150 meters and 0.6 nautical mile beyond the SART position.
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