Hello, I want to have a quadcopter drone type set up which can tell how far from land it is. I would go for GPS but I want it to take into consideration the tide, and in general I'm only talking a distance of 50-200m (within shore fishing distance). The ideal system would be a drone that can traverse along a beach front a set distance from the shore line. Some of the newer drones have sonar for use inside homes but I doubt that is very useful. I'm not that up on the play with what I could bounce off the surface that would show a difference between water and ground. Maybe microwave? I expect though that will have a lot of scatter. My first instinct is image analysis. Perhaps using an IR camera? I've heard that I think CMOS sensors already detect IR and normally have a filter in place. I haven't used image analysing algorithms before. But I'm hoping once I have a drone I can film the shore line to see whether tweaking images produced will allow for a processing friendly derivation of the shoreline position.