I don't know how it is in the UK, or how much real time information is available elsewhere, but in the many floods I've been involved with, uncorrected aerial photography has proven invaluable for immediate operations, and even seeing where the flood is going in remote areas. I appreciate that the UK may not have many of those, but I'm sure that it would still be fairly useful.
As for it's use later on, ground truthing it is not a problem, and it is a valuable extension to the usually limited systematically recorded data.