Even for emergencies like flooding where it is very important to know which areas are flooded and which are not, I think presently there is no satellite based system which can give this information anywhere near realtime with anything close to the required resolution. So in the absence of such I assume the information will have to be gathered from ground reports and areal surveys, which I would think will be extremely time consuming and labour intensive to gather and collate and form a full picture of the flooding.