Would a mission to LEO to study and record the amount of marine debris be of use or is someone already doing it?
It seems the European Space Agency is planning to do it, see this recent article (19 March 2018):
The millions of tonnes of plastic ending up in the oceans every year are a global challenge. ESA is responding by looking at the detection of marine plastic litter from space, potentially charting its highest concentrations and understanding the gigantic scale of the problem. [...]
“What we are now looking at in this new project is to assess the feasibility of direct optical measurement of seaborne plastic waste from satellites. This might sound like mission impossible, but there are reasons to believe it might be indeed doable, at least for certain concentrations. [...]
In particular, plastic has specific infrared fingerprints that are sometimes used in the recycling industry to sort plastic items from other refuse on a conveyor belt.” [...]
Satellite images from missions such the Copernicus Sentinels are being checked against aerial coverage plus ground surveys where drifting plastic is collected from the sea to be assessed in close-up. Initial results were presented last week at the International Marine Debris Conference in San Diego, USA. [...]
Paolo adds, “We hope to get an idea of what kind of concentration of marine litter is viewable from the top of the atmosphere using current technology, or if we’d have to operate from the middle of the atmosphere using aircraft or drones. Or would we have to improve the technology? [...]
The project will deliver a preliminary set of requirements for a satellite to detect marine plastic litter in the shortwave infrared.