Yes, off cours, that's correct. Thanks for pointing that out; as it might be obvious for everyone, let me clarify:
GPS will not work underwater; just a couple of centimeters below the surface you will loose reception. This has to do with the frequency GPS satelites transmit on (10.23 MHz x 120 for L1 and x 154 for L2), and the fact that such high frequencies have little to none propagation through any solid mass.
The Airmar DST800 that we are using is a regular boat echosounder, and designed to be installed on a small boats hull, hence the restricted immersion capabilities. I'm pretty sure though that someone can figure out a way to make this (or other echosounder) depth proof for ROV type depths. Altimeter anyone?
The design of this system is based on the requests of one of our clients, a regional research institute. They wanted to have the possibility to have the ROV working in "surface mode" in order to generate bathymetric maps, but also to dive and capture enviro-chemical data in the water column.
We started off with a kit of Atlas Scientific sensors. A.S. have a board and a lot of resources to go that makes it pretty much plug and play to integrate the different sensors and store the data on an Arduino (and shortly a RPI).
But we where also looking for a way to capture NMEA data and store it, preferrably in the same log, so that our client could easily integrate all the data and generate models that would allow them better understanding of what is happening in our environment.
As I was doing research for ways to integrate all of these data, it quickly became clear that it although great resources exists to do one or the other, I was unable to find anything that would let us do both in a quick and simple manner. So we ended up designing it ourselves.
The EnviroSense can capture simultaneously data from a variety of sensors, and store it in a mySQL database.
The main way I envision this being done or used, is that the vehicle will go to a point, either manually controleld or by waypoint programming. It will store the position, the depth from echosounder and then submerge itself to whatever depth the operator is comfortable with, storing environmental data parsed with pressure from the pressure sensor (Blue Robotics depth sensor mounted on ROV) from the column. Alternatively, without the echosounder, you could submerge the vehicle to the bottom (or MOD). Resurface and repeat.
Another way to use this system is as a multiparametric sensor system: Configure first as CTD, reconfigure for next mission (or next cast) with DO / ORP / Temperature.
We are probably also installing an array on a local aquaculture reserach facility as a permanent installation.
Finally, there are probably a lot more ideas out there on how this can be used, I'm just looking at it from our clients perspective. I'm more than happy to hear your ideas.
As of writing this, we are assembling one of the boards, and I'm hpoing we will have two ready before the end of the weekend. That will give us some time to test it in our test tank, and on Wednesday we have our first field teste together with our client. I'll keeo you all updated with the progress.