The technology of the Nina search

When Osama bin Laden went outside he knew satellites could spot him, so he wore a cowboy hat to hide his face.

With high resolution pictures he was spotted anyway and it is the same kind of pictures that some believe might spot the missing 21-metre yacht Nina in the Tasman.

But the public are not allowed to see them.

Nina, with seven aboard, left Opua on May 29 bound for Newcastle, Australia. It was last heard from on June 4 reporting very rough conditions. On June 25 the Rescue Co-ordination Centre launched a search but found nothing.

Crew families say there is no evidence Nina sank. After raising funds for private aerial searches organised by Texas EquuSearch they have turned unsuccessfully to political lobbying in Washington and satellite pictures from DigitalGlobe Inc which has given them 3.2 million grainy pictures of the Tasman from their five satellites.

DigitalGlobe subsidiary Tomnod designed a crowd-sourcing online tool for 13,000 viewers to explore images covering 500,000 square kilometres. Algorithms combine the crowd's consensus to link important finds. Image 1014398 taken on September 16 captured what they said was Nina. Four days later the rescue centre saw it but felt it was not worth resuming the search as the boat, if it was the Nina, would have moved from the mapped position.

Maritime New Zealand says DigitalGlobe's pictures are difficult to analyse with ships, waves and cloud shadow looking the same but Larry Slack of EquuSearch is frustrated the rescue centre takes limited notice of the pictures.

"The costs are relatively low compared to time and expense of conducting traditional aerial and watercraft searches."

He believed 1014398 showed Nina and said there should have been a quicker reaction. "The issue is not just the timeliness of the satellite images but also the timeliness for response and action."

Maritime NZ safety and response services manager Nigel Clifford says satellite imagery is one of its tools and the availability of commercial rather than classified military images offers additional capability.

"However, the ocean areas around New Zealand are not well covered by satellites and in addition it is very challenging to get usable quality images," he says. "It is also a challenge to process and analyse the images that do exist."

Even if it was possible to pick out a vessel, identification was difficult.

"Overall there is a role for using satellite imagery but it is likely to remain fairly limited."

Unmanned drones offer a limited alternative. While they are cheaper, their data still needs to be analysed.

There are also complex technical and safety issues around operating them in areas where manned aircraft are present.

DigitalGlobe last year had revenues of US$421 million (NZ$502m) with 76 per cent from US military and intelligence agencies, including its largest customer, the National Geospatial-Intelligence Agency, whose analysts saw the tall man in a cowboy hat in a compound in Abbottabad, Pakistan. Last month whistleblower Edward Snowden released documents that showed a fleet of satellites played a vital role in the bin Laden raid.

Google Earth, Microsoft Bing and gaming software also use DigitalGlobe images.

It also works with actor George Clooney's Satellite Sentinel Project which uses satellites to provide warning and deterrence of atrocities.

DigitalGlobe's WorldView-1 satellite defines objects down to 31 centimetres but by American law the public can only get a resolution down to 50cm.

DigitalGlobe says it needs resolution quality restrictions lifted to better compete against non-United States-based satellite imagery companies, particularly as defence spending shrinks over the next decade. Next year's satellite will have the "highest resolution of any commercial remote sensing satellite available", says Walter Scott, a company vice-president.

It will be too late for Nina but with 30 million square kilometres of ocean responsibility, New Zealand might benefit.