This report is a review of the debris detection efforts that took place in the years following the earthquake and tsunami that struck Japan in 2011, as well as valuable lessons for the future of marine debris detection.

Imagine this common scenario: you’re looking into the horizon over the ocean, and you have just spotted an object in the distance. It’s faint and you know something is there, but you can’t quite make out what it is. Chances are, unless you get closer, you may never know exactly what you saw.

This is just one of many challenges scientists and responders face when detecting marine debris in the open ocean, according to a report published in 2014 by the NOAA Marine Debris Program. The report reviews the debris detection efforts that took place in the years following the earthquake and tsunami that struck Japan in 2011, as well as valuable lessons for the future of marine debris detection.

Before the tsunami, some of the detection technologies – including several types of satellite sensors – had not been used before to find marine debris or were in early stages of testing. Because of the extensive efforts and renewed interest in at-sea detection during the Japan tsunami marine debris (JTMD) response, the marine debris community learned more about marine debris’ behavior and movement and advanced the state of knowledge on detection of debris at-sea.

Federal, state, and local partners focused on finding JTMD through several detection methods, including observations from aircraft, unmanned aircraft systems, vessels, shoreline observers, and satellites. NOAA paired detection with modeling in order to focus detection resources on areas where the debris was most likely to be located, given the large area of ocean where the debris dispersed.

“Marine debris is very small compared to the North Pacific, so we needed to try as many different methods as possible to locate it,” said Peter Murphy, Alaska Regional Coordinator for the NOAA Marine Debris Program. “If you shrunk the North Pacific to the size of a football field, even a large object like the Misawa dock is still equivalent to the width of a human hair, and it would be a moving hair. We learned lessons about what works and what doesn’t work, so now we have a toolkit of knowledge on the mix of techniques and when to use them in future projects and responses.”

While there was significant involvement and engagement from the public and agencies at the federal, state and local level in finding JTMD, many of the lessons-learned illustrated the significant challenges and limitations that come into play when searching for diverse objects in a very large area of the ocean. The report explores each detection method used during the response, as well as the limitations of each method and possible actions to overcome the limitations.

One of the biggest lessons relates back to that “faint object on the horizon” scenario, when, for example, a camera cannot distinguish between a piece of debris and a wave crest. According to Murphy, “this is the gap between detection – being able to say something is there but not knowing what it is, and identification – being able to reliably know what it is you’re seeing. This is true when employing everything from the human eye to satellite cameras and sub-surface sonar.”

Researchers now have a better base of understanding to move forward with using remote-sensing technologies for at-sea detection of debris, but the report emphasizes the human eye is critical to the effort, both in finding debris and in providing a “ground-truth” comparison to what can be detected from the air.

“Citizen science has a very high value,” said Murphy. “Even with all of the technology and the many advances, the knowledge of beach users and mariners in identifying ‘normal’ and ‘abnormal’ debris can be a huge benefit in finding pieces of debris.”

Taken together, the results of JTMD detection efforts will help inform future detection efforts and decisions, both for chronic marine debris and for responses to events that create an acute release of marine debris.