What RF transceivers modules are used on AUVs for communication with ground station?

Question

I am working on a project where we want a RF transceiver on the AUV for communicating with the ground station when its on the water surface.

I am looking for RF modules that can work in proximity to water body and can provide transmission range of 5 km with throughput of 10 Mbps.

Can you please suggest me some OEMs that make long range RF transceivers. Also, how do other AUVs use RF with antenna being just some centimetres above from water surface?

I talked with one RF OEM, he mentioned that due to fresnel zone clearance issue we cannot have RF communication for than 200 m for antenna being 25 cm above water. He said that for 5 km range the the fresnel zone radius is 10 m so antenna on AUV should be 10 m above water surface which is not feasible in our application.

So how do other AUVs have RF communication for long range?

Answer 1

I will mention that fresnel zone issues are no joke. When the zone is violated either by the ground plane, or other objects, the transmission will be severely attenuated.

Note however that the shape of the fresnel zone depends on:

1. the frequency used, (higher frequency is a smaller zone)
2. the locations of the antennas, (higher antennas move the zone away from the ground and other objects).

So using low-frequency transmissions to a low base-station antenna may not work, but high-frequency transmissions to a very high base-station antenna might be ok.

Existence proof: the Seaglider AUV. This underwater glider had an antenna that was over a meter long. The antenna communicated via satellite link. (i.e. nearly straight up).