Using nRF52840 to send data over open sea surface

[Harry94]

I am currently working on a project where I try to send data from a swimmer in the open sea to a point on the land (beach). I know that Bluetooth communications are blocked by the water, but would it be possible to achieve this communication whenever the wrist of the swimmer (wearable) is out of the sea? Will the sea environment allow this communication?

[awneil]

Perhaps you need to define what, exactly, you mean by "detect" ?

Remember that we know nothing about what you're trying to achieve here!

http://www.catb.org/esr/faqs/smart-questions.html#goal

If the device is simply broadcasting a "beacon", then you can detect whether that is present or not without having to establish a connection.

Edvin said:

This doesn't sound like a case where BLE would be very suitable

So why, specifically have you chosen BLE?

Have you considered alternatives?

[Harry94]

I selected it because I am familiar with it and because of its range. I have considered more alternatives, but I am doing a research of what is possible. Any directives are welcome.

-Harry

[Edvin]

Harry94 said:

Well, there are two scenarios based on the range. If the the range can reach the shore then yes, it would be a phone. Otherwise, I could connect to an Arduino enclosed in a buoy in the open sea, and then with an antenna communicate with the phone on the shore.

 Well. This is all possible, but you would simply have to test in the conditions that the device will operate in to see whether it will be detected or not. As awneil says, maybe a beacon would be more suitable, instead of actually connecting to the device. 

[awneil]

Harry94 said:

Any directives are welcome

Still unclear what your goal is - what you're actually trying to achieve - so impossible to give much direction.

But I think the main directive is that BLE is not at all well-suited to this.

Note that the nRF devices can also do other protocols but, because of the water... submersion, anything 2.4GHz is probably not going to be great.

[awneil]

Edvin said:

maybe a beacon would be more suitable

But, as already noted, it'll need fast advertising - which will draw a lot of power.

And, if the device is only above the water briefly, it may not be enough for a scanner to "catch" (beacons are usually assumed to be "permanently" visible)