The aged boiling water reactors at the Fukushima Daiichi are the subject of intense scrutiny within Japan and around the rest of the world: The plant was damaged in the earthquake and subsequent tsunami, and since then numerous safety systems designed to shut down the nuclear reactors have failed, resulting in hydrogen explosions that have damaged the reactor vessels and their surrounding buildings. It's hard to determine what's going on inside the tangled mess of collapsed structures, and efforts to contain the reactors are hampered by radiation leaks. Hence the U.S. offer to assist with a Global Hawk surveillance drone. But what can it do?
The autonomous Global Hawk is equipped with a sophisticated radar system that can do far more than the blips and tracks of an air traffic control display you probably imagine when someone says the word "radar." The radar systems onboard the drone can be trained down onto the ground at a long range away from where the aircraft itself is flying. By illuminating "strips" of a battlefield with the radar beam as it flies, the drone can carry out sophisticated surveillance of remote locations thanks to sophisticated computer processing which generates radar images that look a lot like aerial photos—an example, taken by a JSTARS aircraft is shown below.
The drone can even train the radar onto a specific spot as it flies ("spotlight" mode) and garner incredibly high resolution imagery. The stated radar resolution of the Hawk is six feet, but it's reasonable to assume the actual power of the radar package is a secret—such synthetic aperture imaging can result in resolutions as small as one foot.
Since the Global Hawk doesn't have to fly directly over the damaged reactors to record its images, it's possible it's being used to generate very high resolution images of what's going on inside the damaged reactor buildings, in a way that's not possible with direct observation from helicopters due to the risk of radiation contamination.
The sensor package on Global Hawks also includes complex infra-red imaging systems that, under battlefield situations, work in collaboration with the radar systems—the combined imaging and heat-signature data can be used to identify vehicle and building targets, identify hotspots on vehicles that recently ran their engines, and even target heat blooms from people.
In the case of the Fukushima reactors, the Global Hawk's IR sensors are probably being used to generate very high resolution images of the reactor containment vessels—the thick metal "bottles" that shield the actual reactor "core" from the outside world. The big worry in this situation is that hydrogen gas explosions may have cracked the vessels, or leaking partially-melted nuclear fuel rods have, and that dangerous radiation leaks may result. The drone's IR images will certainly be able to aid with working out where hotpots on the damaged reactors are, and thus where technicians and engineers are best directed to try to seal up or stabilize the structures. To see how detailed the Global Hawk's imagery is, check out the image below—a shot of a damaged cathedral in Haiti.
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[Image by Rennett Stowe]
Read more coverage of the Japan earthquake.