I do many flights in urban areas so I have the luxury of being able to place any white mark on bitumen and have it very identifiable from most altitudes I fly. I use chalk paint so as to not permanently deface the landscape. I’ve also been pushing the contrast in order to figure out the lightest surfaces I can still have a visible white mark on. This has resulted in me marking light coloured concrete sidewalks, and dirt. Circle and dot target very easy to find quickly when browsing the aerial photos. If I don’t have hard surfaces I use a roughly 1’x1’ black painted craft wood board with approx 30-40mm white dot in the middle.
