Tracking Tsunami Debris via Satellite

Thursday, June 21st, 2012

by AJ Plunkett

Using satellite imagery to look for tsunami debris floating across the Pacific Ocean toward the west coasts of North America — it’s not as easy as you might think.

A U.S. National Oceanic and Atmospheric Administration (NOAA) official was grilled last month by U.S. senators. The senators wanted to know what was being done to keep track of the estimated four million-plus tons of debris washed into the ocean by the March 2011 tsunami that engulfed the coast of Japan.The senators from West Coast states were concerned that NOAA officials were not pressing hard enough for more access to high-resolution satellite imagery. But according to a report released earlier this year from Fisheries and Oceans Canada, it’s not the access to the high-resolution images that’s the difficulty.

It appears to be more of a problem of math.

The satellites can get a close-up resolution of between one and two meters in area. But there are more than 7,000 kilometers between Japan and North America’s western coast — or seven million meters of ocean. In others words, you have to know where to look.

While estimates are that the tsunami washed about 4.8 million tons of debris out to sea, nearly 70 percent of that is believed to have sunk almost immediately, according to the report. The Japanese government estimates that 1.5 million tons remain afloat, although that remains unconfirmed from other sources.

Conventional satellites were able to track the debris field for about a month after the tsunami. But as debris sank and began to be kicked around by ocean currents, regular satellite images lost track of where it was all going. According to the report, models forecast that much of the debris will remain in the ocean, collecting in the so-called North Pacific Garbage Patch, where it could swirl for years.

In December 2011, the NOAA took model simulations of where the debris was most likely to travel and crossed that with high-resolution satellite imagery to hone in on a 50-by-60 kilometer area where they expected to see tsunami debris. As it turned out, the debris wasn’t there.

“This result means either that scale of the debris was smaller than the 1–2 meter resolution of the satellite imagery, or that debris was not in the forecasted location,” the report states.

Some estimates are that debris could have spread out over hundreds of thousands of square kilometers. And the report notes that a 500,000-square-kilometer area is somewhere between the size of the state of California and the Province of Alberta.

Of course, the debris can still be spotted directly by aircraft and drones, or by commercial vessels traversing the Pacific. However, of some 97 direct sightings between April and the last recorded sighting, which was in November 2011, only two have been confirmed to be from Japan.

That’s one of the other difficulties — figuring out what debris is from the tsunami and what’s just (sadly) normal ocean trash.

While debris from Japan has washed ashore in North America, the vast majority of it may never go anywhere, according to the report. And the largest part of it might not arrive until next year.

What impact the debris might have depends on what shows up. And, until it does, there’s really no way to quantify whether there’s a real danger.

Basically, the only thing to do is to wait. And keep an eye out.

AJ Plunkett is a freelance writer in Virginia with experience in covering defense and aerospace industries as well as the military. AJ blogs via Contently.com.