Underwater Wireless sensor Node

For our final year project we want to make a sensor node that can be used in underwater Wireless sensor networks (sensing parameters can be anything-temperature/pressure)

Since this is underwater the transmission(upto 10ft underwater and then around 10 ft above water till the laptop) will take place using an acoustic modem.(We are still trying to find suppliers from where we can buy an acoustic modem or else we have a paper and may try to make our own using that as a reference).

Underwater node will be having sensor, controller, acoustic modem all encased in watertight box
Surface buoy will have acoustic reciever and a ZigBee/WiFi transceiver.

There are two methods for transmission that we will be trying:

  1. Directly from the underwater node using acoustic modem to surface base station.
  2. From underwater to a surface node using acoustic and then convert to RF then use a ZigBee/WiFi module to transmit to base station (laptop).
    (We are considering these two methods since we are unsure if the first method will directly work)

Questions:
1)Can method 1 directly work or is a buoy necessary?
2)Can we use Arduino for this project?
3)How to interface all the components?

I'm not very familiar with submarines, but I'd use a surface (or sub-surface) receiver, with cabled power and data connections. At least the receiver should stay under water, to eliminate a water-air sound transition. The description of your "network" (how many sensors?) and base platform (ship? stationary?) is not very informative.

Arduino will be able to do this kind of things. Reading sensors, sending out data, typical jobs for Arduinos.

Getting data out from under water is a problem. I have no idea about acoustic modem - whether that even works. I guess it's much easier and more reliable to wire your sensor to a buoy, and have it take care of wireless communications.

I doubt an acoustic modem will work at all. Your only chance is if you modulate some ultrasonic signal, with your data. Then demodulated it before applying it to your acoustic modem. However I think the data rates would be too high.

In water radio waves are not only attenuated but suffer a severe frequency shift so reception frequency in air is not the same as transmission frequency underwater.

In water radio waves are not only attenuated but suffer a severe frequency shift so reception frequency in air is not the same as transmission frequency underwater.

I quite agree with the enormous attenuation, but why should there be a frequency shift? Could you point me at some literature for this effect? The propagation speed will be reduced proportionally to the refractive index of water, but I'd have thought that unless moving at close to the speed of light in the medium, the frequency will be unaltered.

My analogy would be that of light - just shorter em radiation - If I put a light source with a given spectrum - eg a green LED - underwater, and observe it from above water in the air, it's colour ie it's frequency is unchanged.

Allan

Radio waves do not undergo "frequency shift" in water, but expect attenuation to limit the range to a couple of meters, except for extremely low frequency signals.

Sound at low data rates is certainly possible, however you might need transducers intended for submersion in water for efficient coupling, and they are expensive.

Consider a modulated light signal (e.g. blue LED) as a transmitter, also low data rates.

Your research has undoubtedly found this study: www.mdpi.com/1424-8220/16/6/890/pdf

But it was one of the first Google found for me. Had answers to your questions, and much more.

Paul

Grumpy_Mike: In water radio waves are not only attenuated but suffer a severe frequency shift so reception frequency in air is not the same as transmission frequency underwater.

IIRC, the frequency stays the same and the wavelength is what changes when the speed changes.

(Though I'm coming at that from a purely physics point of view and not any real experience with radios so I may be missing something else)