My next raspberry pi idea, need your thoughts

I've seen Dave akermans balloon project with raspberry pi, my idea is for a raspberry pi, gps module and mobile data to communicate with and possibly a short range radio to track the device when its time to retrieve it, all stuck in a vacuum flask or waterproof container with a silica salts bag to control condensation, drop it off at the start of a river and follow it. Batteries will be a concern so maybe something that can wake itself up on the hour, send its current position either by text, data or tweet and then power down to save battery life. 

Any ideas or links to similar projects would be gratefully recieved.