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I Spy… Marine Debris: At-sea detection adventures from the air

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Here’s how science works sometimes. You plan and plan and then something breaks and it all falls apart. Or you plan and plan and later in the game, a new component gets added. Or both, in this case. A group of researchers, technical specialists, and people like me met a couple years ago at a workshop on at-sea detection of derelict fishing gear. For the last six or eight months, NOAA and NASA have been planning a test of a synthetic aperture radar (SAR) instrument that can see through cloud cover to detect ocean features that might accumulate marine debris. This particular SAR is designed to be mounted eventually on an unmanned aerial vehicle (UAV), so it’s called a UAVSAR. It’s not yet ready for flying on the UAV, so for this test it was going to be mounted on a Gulfstream 3 jet. Sadly, about a week before our planned flight, the antenna on the UAVSAR malfunctioned, and it had to go back home to California. However, we were lucky to have gotten the US Coast Guard interested in the project; they offered to fly people over the ocean to look for debris while the UAVSAR looked for those areas of the ocean that might accumulate marine debris. Even though we lost the NASA plane—and thus the UAVSAR—the Coast Guard offer stayed on the table.

Map of the N. Pacific Ocean showing the area of the STCZ.

It’s been six long years since the last flights to look for marine debris from an airplane over the North Pacific subtropical convergence zone, a known area of marine debris accumulation (see map above; for more info on this click here). On Monday, April 11, eight intrepid observers—representing five NOAA programs and Tetra Tech, Inc.—set out to join a Coast Guard training flight. The ocean area of interest was chosen based on our planning for the UAVSAR flight, and it worked just fine for the visual observations as well. Maps of likely debris accumulation locations were prepared using sea surface temperature and photosynthetic chlorophyll data from satellite sensors. The debris estimated likelihood index (DELI) map that averaged data from the two weeks before our flight shows the areas we expected to see more debris (below map image; darker reds) and our planned flight tracks. An explanation of the concept is located in previous posts, here and here. Our planned flight tracks covered areas with both high and low expected debris density.

DELI map image. Courtesy of NOAA.

We had a safety briefing at 7:30am and were in the air a little after 8:00. We transited about three-and-a-half hours north then dropped to between 500 and 1000 feet altitude for about four hours to look for marine debris. All of the observers had training on what we were looking for, how to call out sightings through the headset intercom system, how to record marine debris and weather observations, and what our roles would be. Each observer had a chance to work each of the stations: the four observing ones—left cockpit, right cockpit, left wing, and right wing; data recorder; and an additional recorder.

Photo of Kevin Kelly, Tetra Tech, demonstrating the headset intercom system (unplugged).

A few observing observations:

  • When you’re on a big airplane, 500 feet elevation seems startlingly close to the water. Still, we couldn’t distinguish small items, which may have been out there.
  • It’s a darn big ocean, and even with a fast plane and great conditions, you can’t sample much of it on a huge tank of gas. Even traveling for four hours at 300 km per hour (~200 mph), we did four lines totaling maybe 1200 km (~745 miles). Our swath of observations was at most 1000 meters wide (and honestly, the vast majority of our observations were much closer than 500 m from the plane), meaning that we covered about 1% of the box our tracks outlined.
  • Visibility was not bad but not great. We had to descend sometimes to get beneath the clouds, experienced fog that limited the distance away from the plane we could see clearly, and part of the time had to contend with whitecaps that mimicked white debris items. Still, much of the time we had a clear view at least close to the plane. Our chief scientist is working up the data, but in broad numbers, we saw just 56 items over four hours. Over half were unidentified marine debris, about one-quarter were fishing floats, and the remainder were buoys, lines, cardboard, and nets. How and if the marine debris observations correlate to estimates of debris density remains to be seen. But just getting out there and getting some eyeballs on the ocean surface was valuable.

Author: NOAA Marine Debris Program

The NOAA Marine Debris Program envisions the global ocean and its coasts, users, and inhabitants free from the impacts of marine debris. Our mission is to investigate and solve the problems that stem from marine debris, in order to protect and conserve our nation's marine environment, natural resources, industries, economy, and people.

One thought on “I Spy… Marine Debris: At-sea detection adventures from the air

  1. Since you have access to a C-130, is anyone looking into modifying the LM developed sensor pod that fits onto a C-130? If memory serves me correctly it was being developed by Skunkworks for DIA.

    Also, could you pot the info that led you to test a SAR instrument rather than a LADAR sensor?

    And finally, your post indicates flying only with a swath width of 1000M, which is pretty darn narrow. Was this b/c of the resolution of the sensor relative to the size of the targets you were looking for, or b/c you needed visual confirmation of what you were detecting with the SAR?

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