Imaging Technology
Aerial cameras can be broken down into six components: lens assembly, focal plane, lens cone, body, drive assembly, and magazine. Of these the lens assembly and magazine are the most crucial as they determine the image coverage and detail, and how many images can be collected respectively (10).
Camera Positioning
There are three angles at which aerial photographs are taken: vertical (NADIR), low-oblique, and high-oblique. Most photographs taken for plastic detection are from the vertical angle (2). In some cases, altering the angle from the NADIR position allows for increased detection levels, such as, if the plastic litter is hidden beneath vegetation (46).
Image Processing
Using computer algorithms and Machine Learning (ML), the photos taken can be analyzed to identify and classify objects within. This is possible due to the unique optical properties of floating materials in comparison to the surrounding water. Plastics and natural debris have unique spectral reflectance levels in the near infrared (NIR) and shortwave infrared (SWIR) light ranges, unlike the ocean, which is a dark target with low reflectance (7).