Reutech Radar has developed a passive ship navigation radar receiver that can detect 'dark' vessels that have switched off their AIS transponders, but not their navigation radar.

Anthony Green, Specialist: Systems and Solutions at Reutech Radar Systems, told defenceWeb that the RIS 100 Navigation Radar Intercept Sensor (NRIS) came about from the fact that although vessels may switch off their Automatic Identification System (AIS) transponders, they are highly unlikely to switch off their navigation radars, as this would constitute a major safety hazard.

When vessels deliberately switch off their AIS transponders, it is highly likely they are doing something illegal, such as illegally fishing, smuggling, dumping waste oil at sea, engaging in piracy etc. Sometimes vessels turn off their AIS for good reason, such as trying to avoid pirates in dangerous waters like the Gulf of Guinea, but such actions are in the minority.

"Going dark" is especially common among trawlers engaged in transshipment, or the illegal transfer of fish from one vessel to another. Illegal, unreported and unregulated (IUU) fishing costs West African nations alone $2.3 billion each year, according to the United Nations, but is a worldwide problem. It is estimated that only 20% of Chinese fishing vessels of West Africa switch on their AIS.

AIS receivers have been in use since 2008 and were meant to support safe navigation and collision avoidance by automatically transferring information about a vessel to other ships. AIS has increasingly has been used in fisheries enforcement.

One method of detecting dark ships is to use radar, but that requires an active radar signal, which could in theory be detected by the target vessel. Reutech's NRIS is passive, so it is highly discreet. Green told defenceWeb that Reutech's system is the only such solution in the world.

One NRIS system has been installed at the Slangkop lighthouse in Kommetjie for trials. The system has already received its first order, from a southeast Asian customer, and according to Green has been very well received.

The RIS 100 NRIS is a Radar Electronic Support Measures (R-ESM) receiver that covers the X-band marine radar frequency (S-band will be added at a later stage) and provides a bearing line (strobe) on the emitting radar. "The accuracies delivered by the sensor allow for correlation between RIS 100 strobes, Automatic Identification System reports and, if available, radar tracks to identify commercial shipping that have not activated their AIS transmitters," Reutech explained.

The sensor may also provide early indication of a vessel approaching from over the horizon since the mast-head navigation radar may be detected before a vessel's own radar detects the hull of the arriving vessel.

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