Drone surveying of invasive non-native plant species on rivers

My company needs to generate accurate data on the abundance and distribution of a number of plant species on UK rivers (Japanese Knotweed, Giant Hogweed, Floating Pennywort and others). We are carrying out surveys on the ground using GPS recording, photography and other information about the sites. I would like to test the potential for using drones to produce high quality images (easy) with accurate GPS positioning (also easy) and then, either automatically or using a desk-based operator, identify the plants and approximate areas (not so easy). These plant's distributions vary year on year and so up to date information to help plan and deliver treatment programmes is essential.

I think the other not so easy aspect of this project are the practical issues of flying drones along rivers with public access and spotting vegetation sitting under overhanging trees but since drones seem to be the future for everything, I think it's worth investigating and piloting.

Any suggestions welcome.