Similar to this question, a need a wireless transmitter for underwater, both fresh and salt water. Vertical range needs to be a few 100 meters, and underwater depth only 2 meters. The power supply will be a battery and the device needs to be able to run for a few hours.
Receiver will always be above water. And only one-way communication is necessary. The data that is sent is only a few bytes big, or two (decimal) floating points representing coordinates.
Any ideas in which direction I should start searching?