Fill your boots, there's an international organisation dedicated to solving exactly this problem.
ISARRA ? International Society for Atmospheric Research using Remotely piloted Aircraft
I'm no longer very engaged with them, but have been to a couple of their conferences, and the best practitioners are absolutely superb. The best people in the UK last I looked were either at the University of Birmingham, or SAMS in Oban - but I may be out of date on that.
G