What technology is the private rescue firm using to search for missing Nicola ... trends now

As the river search for missing dog walker Nicola Bulley continues through a second week, a private diving firm has been called in to assist with high-tech equipment.  

Specialist Group International (SGI) began aiding the search for Ms Bulley in the waterways of St Michael's on Wyre village in Lancashire on Monday morning and continued into a second day on Tuesday. 

Surrey-based SGI, which has offered its services 'free of charge', is led by forensic expert Peter Faulding, who carries out underwater search operations for police across the whole of the South East.

He said his team uses a high-spec sonar worth £55,000 'which can see every stick and stone lying on the riverbed' and is 'more superior' than the sonar equipment officers have at their disposal.

Here is a guide to how SGI's kit – including remotely operated vehicles (ROVs) and magnetometers – compares to the sonar, scuba gear and specialist search dogs used by police divers.

TECH USED BY SPECIALIST GROUP INTERNATIONAL

SGI is using a powerful type of sonar equipment, called side-scan sonar, which helps to create large images of a seafloor or a riverbed and detect objects. 

The high-frequency device is towed beside an inflatable dingy that carries a small team of staff.  

It uses multiple physical sensors – called transducer arrays – at the bottom of the moving vessel that sends and receives sound pulses.

As the vessel moves along its path, these sensors send out signals on both of its sides, sweeping the seafloor like the fan-shaped beam of a flashlight.

Side scans search at constant speeds and in straight lines, allowing the vessel to map the ocean bottom as it travels. 

Side-scan sonar is a particular category of sonar, a technique that uses sound waves to 'see' through water and detect underwater objects, but side-scan is generally better suited to shallower waters such as rivers. 

SGI's Faulding, an ex-paratrooper turned search and rescue specialist who calls himself a 'human mole', told Sky News: 'We're bringing a particularly high spec piece of equipment, 1800 kHz Side Scan Sonar. 

'It's very high frequency. It's about £55,000, and it scans the river and I can see every stick and stone on the river bed, and we've got a very high hit rate with this.

'Each year we deal with a lot of drownings and we locate them extremely quickly. The difference with this sonar is that it's very, very high frequency.'

SGI's specialist sonar equipment did not find anything on Monday after scouring three or four miles of river. 

Faulding said his team would spend Tuesday searching through another stretch of river towards where Ms Bulley went originally missing, which was already covered by police divers in the days following her disappearance.

However, SGI is going back over the area using its sonar. 

Emma White, one of Ms Bulley's friends, said on Monday that her worried family had asked Faulding and his company for help.

'Following the hypothesis of the police that Nicola was in the river, we need some evidence to back that up either way,' she told BBC Breakfast.

'I feel Peter and his amazing bit of kit … is going to come and sweep the river bed and give us answers.'   

SGI says on its website that it also uses remotely operated vehicles (ROVs) – unmanned machines that are controlled by staff from afar.

ROVs are either tethered or untethered to a bigger surface vessel and operated using a joystick, almost like the controller of a gaming console. 

The firm also uses magnetometers – devices that measure the strength and sometimes the direction of magnetic fields – although it's unclear if they're being used in the search for Nicola.  

EQUIPMENT DEPLOYED BY POLICE

Before SGI was called in, Lancashire Constabulary was deploying drones, helicopters and police search dogs as part of the major missing person operation, while in the water specialist diving teams have been using scuba equipment. 

Divers from the North West Police Underwater Search & Marine Unit, which serves the Lancashire area, also have a side-scan sonar, Faulding said.

But he added that 'our sonar is probably a bit more superior'.

The unit does use such technology to search large areas of water, but it is a 'sub-surface blind fingertip search' for items such as weapons or phones that is their most common method of search. 

Earlier in the search, a team of frogmen trawled beneath the surface of the River Wyre, while other officers on a boat and accompanied by a specialist search dog scoured the water surface.

The police are also understood to have a fleet of remotely operated vehicles that they can deploy, but it is unclear if these have been used in the search so far. 

According to Faulding, police used scuba divers and sonar equipment of its own, although its version of sonar 'is pretty low-tech'. 

'It's very unlikely they

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