In order to evaluate the quantity of floating marine litters it is essential to know the probability of detection of these objects.
The activities by the ECOLE PRATIQUE DE HAUTES ETUDES
In order to evaluate the quantity of floating marine litters it is essential to know the probability of detection of these objects (which is function of their size, shape, colour, distance from the vessel of observation, etc.). An experiment was set up to define the probability of detection of specific floating objects at sea.
This protocol consists in:
- Making square plates of extruded (floating) white plastic of different sizes (according to the MSFD size class: 1; 2.5; 5; 10; 20; 30; 50 cm side). These plates are independent from each other and ballasted by a weight attached to the plate by a nylon line to prevent them from drifting (All equipment is removed once the experiment completed).
- Placing these plates along a defined pattern (with respect to their size, number and distance to the boat), using a telemeter to visualise the exact position of the objects from the boat.
- Having one observer (who ignores where plates are located and what kind of litter he is looking for) on one side of the boat (fishing line is placed on the boat to visualise distances) with a secretary that notes the marine litter observations of the observer (type of litter, number, colour, size and distance to the boat) on a dedicated datasheet.
- Carrying out transect replica (20-minute-long at 4 knots with Beaufort < 3).
- Testing a pole camera and drone for the detection of these floating objects.
Figure 1. Observer (in the middle) showing a detected object, secretary (on the left) and pilot (on the right)
Figure 2. Experiment to define the probability of detection of floating marine litters in progress (picture taken by a “Phantom 4” drone)
Figure 3. Extruded plastic plate ballasted with a weight to prevent it from drifting