The joint navy and police dive teams in Wanaka this week are using sonar scans and underwater cameras to conduct their lake search.
The sonar equipment uses soundwaves to detect dense objects lying on the bottom of the lake.
The side-scan sonar, otherwise known as a remote environmental measuring unit (Remus), is an autonomous, wireless underwater vehicle that looks like a torpedo and flies like an aircraft under water, Lt Cmdr Andrew McMillan, of Auckland, said.
The Remus is pre-programmed with a set course and area and then deployed.
It can go to a depth of 100m and runs in lines backwards and forwards across the lake bed, sending feedback during its mission to people monitoring it from the surface.
The data is recovered once the mission is over and downloaded to a computer for analysis.
Objects of interest - and, unfortunately, rocks - show up on the scan as blurry shapes.
The next stage in the search is to retrieve close-up photographs of objects using a remotely operated vehicle (ROV) with a camera on board.
Unlike the side-scan sonar, the ROV can go to 300m, but it is not used in the initial stages of a search because that would be "like searching a rugby field with a penlight", Snr Sgt Bruce Adams, of Wellington, said.
The ROV has a video feed and provides live footage of its mission, allowing operators on the surface to identify objects.
Some ROVs have retrieval arms on them, but the one being used in Wanaka by the navy does not.
Commercial operators around New Zealand have them, and they can be contracted by the police or navy as required.
In the military arena, the navy uses the Remus and ROV technology to map the sea floor and find mines.
