As space-based remote-sensing assets assist in the hunt for Malaysia Airlines Flight 370, multiple satellites from different nations are imaging a massive search area stretching from Kazakhstan to the remote South Pacific in an attempt to locate signs of the missing Boeing 777-200 aircraft.

U.S. commercial remote-sensing-services provider DigitalGlobe says Australian authorities have used the company’s high-resolution satellite imagery to locate two large objects in the Indian Ocean near Perth that could form part of a debris field associated with a potential crash site.

The panchromatic and multispectral images were captured March 16 using one or more of the Longmont, Colo.-based company’s five high-resolution Earth observation spacecraft. They indicate two objects, one as large as 24 meters (79 ft.) long, floating some 2,500 km (1,550 mi.) southwest of Perth.

John Young, general manager of the emergency response division of the Australian Maritime Safety Authority (AMSA), said the images provided to Canberra authorities were assessed March 20 by the Australian Geospatial-Intelligence Organization (AGO).

“We have been in this business of doing search and rescue, and have used satellite images before, and they do not always turn out to be related to the search, even if they look good,” Young said during a March 20 news conference in Canberra. But he said the AGO analysis appears credible enough to divert AMSA’s search.

On March 11, China’s meteorological agency requested activation of the International Charter for Space and Major Disasters to assist in the search for the missing plane. The group of 15 national and international space organizations supplies space-based remote-sensing assets free of charge in response to natural or technical disaster relief efforts.

As part of the search effort, DigitalGlobe is using its Tomnod crowdsourcing platform to engage the public in the hunt for the missing aircraft. The company has tasked its constellation—including sub-meter-resolution satellites WorldView-1, WorldView-2 and GeoEye-1—to capture images of the Indian Ocean and surrounding areas, and is uploading archived and new imagery to the site, where amateur data analysts can peruse pictures and tag potential signs of wreckage.

Since the aircraft went missing, Tomnod has added upward of 3.6 million participants and generated more than 385 million map views on the site. Tomnod uses a CrowdRank algorithm to identify overlaps in tagged locations before they are culled by DigitalGlobe analysts, though it is unclear whether the tool played a role in identifying the March 16 data provided to Australian authorities.

In the meantime, Young said commercial satellites were recently redirected to take additional high-resolution images of the areas of interest, and that further imagery is expected “in due course.”

In addition to DigitalGlobe, Germany’s commercial remote-sensing services provider BlackBridge is offering a similar crowdsourcing capability, with images from its five-satellite RapidEye synthetic aperture radar (SAR) constellation loaded onto a MapBox platform. Airbus Defense and Space—formerly EADS-Astrium Services—is also supporting the effort, tasking the French high-resolution Pleiades 1A and 1B satellites and medium-resolution Spot 5 and Spot 6 optical imaging spacecraft, as well as the German SAR satellite TerraSAR-X, to capture images of the search zone.

France’s Pleiades spacecraft delivers 70-cm (28-in.) resolution images in black and white, which can be resampled to 50 cm with a swath width of 20 km. Spot 5 and 6 offer medium-resolution imagery between 1.5-2.5 meters resolution, and a much wider field of view (60 km).

Philippe Campenon, director of space and Earth observation at Paris-based Euroconsult, says radar and optical imaging satellites with 5-meter resolution or better have the best chance of spotting the aircraft.

“If a plane has landed at an airport, even a small airport with no warehouse to hide it, a satellite with 15-meter resolution could find it, but it would really be kind of a big dot,” he said. “With 5-meter resolution you will see the fuselage and the wings, maybe some shape of the engines. At 2.5 meters you can definitely see it is a jet plane, and of course at 1 meter, experts could tell you it is a 777.”

Campenon said some satellites can see objects just below the ocean’s surface, “especially those with very good blue-band, which have the capacity to see in shallow water.” Among the satellites providing optical data collected over the search area, he said DigitalGlobe’s Worldview-2 has a very slight advantage.

“It has several blue bands, so they can filter what corresponds to the atmosphere and what corresponds to the sea or any alien object,” Campenon said.