Over the last few years, from time to time there appear publications, press releases and even startups for divers. The point is it is still considerably less convenient to navigate underwater and the type of tools available for surface-based marine navigation leaves it behind: GNSS signals do not penetrate into the water, while the existing inertial systems are either not accurate enough for this purpose, or too expensive.

I’d like to tell you how the three of us made underwater GPS possible within a year from scratch.

In general, the necessity for making a simple underwater positioning system became crucial long time ago. It’s not that I’m claiming there’re no such things as the underwater positioning systems, on the contrary, one can simply stumble upon them: from super serious HiPAP (Norwegian firm Kongsberg) and GAPS (by IXBLUE, France), an entire line of systems from the German EvoLogics.de, American Teledyne, English Sonardyne, to relatively simple Tritech MicronNAV, Israeli UDI (one of the very few systems divers can use). For your reference, one of the simplest positioning systems (MicronNAV) costs an average of 18,000 euros, and is designed as a robot-based solution (ROV) for distances only up to 500 meters. And Israeli UDI which was originally developed only for divers, mostly, solves the task of pre-set messages sending (up to 14 pre-set messages) and offers a very simple function of navigation — the only possibility of which is to enable the diver to get to the beacon (access to the beacon only — without geographic coordinates, without the possibility of getting to a definite point in the water area and so on).

When underwater, the diver is not having a very good time being challenged with the hostile environment, the limitation of the amount of air in the cylinders, poor visibility (sometimes, within the arm’s-reach range), not to mention the constant water pressure. Any diver will tell you that deep water does not forgive mistakes and it’s true when they say it is easier to launch people into space than to send them in a submersible six thousand meters deep.

Take a look at a list of manufacturers of underwater vehicles, the number of which is larger than that of car brands familiar to me.

But having cast the underwater vehicle does not mean the principal problem is solved: you can get real-time HD video captured from the device-in-question, but there’s an almost inevitable problem of understanding where exactly the device you have lowered underwater is located. Besides, where is all of this that you have seen in luxurious quality on the monitor. And we are leaving aside the risk of breaking the hi-end apparatus against the dive boat when returning to thе surface because of uncertainty of its position.

Well, why is it so hard to solve the problem of navigation underwater?

The radio waves should be excluded, as for the light, it fails to reach far enough in real-world murky waters; thus, there’s only the sound left.

Many different companies, other creative teams as well as individual developers have been trying to solve this problem. Some of the proposed solutions have no obvious relation to reality, Navimate, for instance, has been promising sales since 2009, having provided nothing but renderings. Experts have already buried it, still, this “startup” does pop up on miscellaneous diving forums every now and then.

There is another interesting concept — an inertial navigation system our team vigilantly keeps track of, yet it got stuck upon 3D-printing a prototype stage, decorating the table. And there is a couple of NaviMate clones left: Concept 1 and Concept 2.

Physics is one for all, thus, enabling us to prove in detail why it is impossible today to design a system providing the features and the form-factor claimed by the “startupers” whom we wish good luck, but it is not the issue to be discussed in the article.

There are also many systems with a GPS antenna on the cable with a float, for example, this one or that one, still, to be honest, they are not one can call “underwater GPS”, besides, it does not happen so often that divers get a chance to be able to be moving underwater with a float on a rope.

Among those inspired by underwater GPS issues there are DARPA guys, yet, they haven’t shown us so far anything but impressive pictures.

I can hear some readers shout “Well?..,- with a stamp of the foot against the water surface, — “Apparently, this issue might be of the same kind as human quantum teleportation or (yeah, at least!) launching the very same man to Mars in conventional ways (on a huge rocket). So, let’s forget about it because it is not so easy to make an underwater GPS system!”.

Yet, what if I tell you the three of us have managed to make an underwater GPS system in a year?

We did cope with it cause we could not stand the idea that it’s impossible.

I’d like the readers to understand me: It’s not that I’m looking for advertising, underwater navigation is a very specific thing, and I have already reached out to quite a few names interested.

I just want to present an absolutely our product — from start to finish.

Small disclaimer here: as we had pretty tight schedule and lack of resources, we somehow skip a part of press-releases, selling materials, future promises, e.t.c. So I have to describe a real thing with real results in real environment. And, yes, it’s selling and working as well, you can check it out.

Now, I’m going to be as brief as possible to tell you how we did it. Well… ‘as brief as possible’ doesn’t mean ‘brief’ in general.

So, here’s a big picture featuring types of navigation systems, with their pros and cons:

The systems are divided according to the so-called relative length of the measuring base. The length is measured relatively to the sizes of the track of the object to be positioned.

- Ultra-short base-line (USBL) In fact, this is positioning based on determining the direction of the signal source. The system basically consists of a DF (direction finding) antenna and a responding beacon. The antenna transmits an interrogative signal, the beacon responds to it, according to the signal propagation time, the slant range is computed, the antenna determines the direction of arrival of the signal — the vertical and horizontal angles, thus, positioning the responding beacon with respect to itself. Some of the disadvantages of systems like these are strict requirements to the antenna geometry, the necessity of consideration of its position while submerged — the impact of oscillatory motion, if the antenna is lowered on a cable — it is spinning around, the antenna slopes, you want to to mount a magnetic compass on it. Besides, the beacon must have good energy characteristics, because when several beacons being used, they are being queried sequentially. It’s not much like a GPS, but that’s the way our ears work.

- Short base-line (SBL). If you spread the elements of the DF antenna somewhat farther away from each other, for instance, if they are hung on the broadsides of the dive boat, you will get a short base-line system. Since the distances between the transducers are significant, it’s already possible to gently try to directly solve the problem of determining the location of the signal source. In fact, the very elements of the spread antenna can become the signal source, and reception can be performed by the beacon, in this case, the coordinate is calculated on the object being positioned. Actually, it is much closer to GPS because with the arrangement of the system like that the beacons can be completely passive acoustically, from now on, they become navigation receivers, as well as GPS/GLONASS ones. However, in this case, the size of the measuring base is not sufficient to obtain adequate accuracy — here, one can draw a parallel with the measurement of parallax in astronomy — the measuring base in that case is the size of the Earth’s orbit in diameter and the farther the star, to which the distance is measured, the less noticeable its migration.

- Long base-line (LBL). In fact, this is the same short base-line system, but its elements are arranged independently on the sea bed or mounted on floating platforms. In this case, everything seems to be absolutely fine — the measuring base dimensions are adequate, the base stations themselves (the elements of the navigation measuring base) are functionally similar to the GPS/GLONASS satellites.

The disadvantage of this system consists in the inconvenience of its deployment, and in the case of the sea bed base — first, you want to accurately determine the coordinates of the sea bed stations — and here we are, at the same point we started from.

But, as a sailor I used to know kept on saying, “Do your best — the worst will happen by itself”.

If we are going to make an underwater GPS system, let it be as similar to a usual GPS one as possible. You know, millions of cars and people equipped with smartphones move on the ground, in most cases, they do get where they want to and no one measures the distance to GNSS satellites in a query-response way, as for satellites, they provide mere emission, receiving the return signal and the whole situation looks pretty bright — everyone is satisfied.

What are the musts for a system of this kind? They are quite basic — you’ve got to know where you are against any predefined marks, i.e. points of interest (POI), you want to have your trace recorded during a dive to review your motion after the entire dive, it would be nice to be able to set a “waypoint”, if you spot something remarkable underwater to return to the location later. What fundamental problem do you have to solve to turn it all into reality? The only thing you need is just to be aware of your absolute geographic coordinates while in a submerged position. You know how to do it, you’ve got all bases covered.

At a very early stage, when our system was in the “sketches on napkins” form, we set our mind on the LBL paradigm.

Our system requires exactly four “satellites” — buoys that are equipped with GPS/GLONASS receivers to determine their own coordinates and to transmit the coordinates to an unlimited number of navigation receivers later. It means that unlimited (Like the boss can do it!) number of the receivers, according to the data obtained, can position themselves — but not against the buoys as it is with the SBL, no, I’m talking earth coordinates!

Briefly, the system consists of four floating buoys functioning as GNSS-signal retransmission bases, and any number of subsea navigation receivers;

In our system, the navigation receiver is acoustically passive — it never emits (that’s how you enable an unlimited number of acoustic receivers to be functioning in the same waters), the receiver “listens” to the buoys, receives their messages and solves the problem of finding their own position on the basis of geographical coordinates of the buoys. OK, you know the lat/long positions and that’s when depth calculation comes into play — and voila, we know where exactly our navigator is in the water!

For the first time, the system was presented at IMDS-2015 (International Maritime Defense Show), traditionally held at Lenexpo fairgrounds in St. Petersburg. The “underwater” audience took a great interest in the system; That was followed by numerous trips to various waters of Russia. During each trip we were accumulating factual material which enabled us to improve both the “hardware” component of the system and the algorithms.

Now let’s take a look at how it all works.

The diver-based receiver/display unit

Upon obtaining lat/long position, the diver’s navigation receiver displays the calculated azimuth and distance to the selected destination point — set before the dive, saved during a dive or to one of the four transmitting buoys.

Accordingly, we need to equip the receiver with a compass, so the diver is capable to head along the azimuth specified by the device. However, divers we had worked with would criticize us for using the electronic compass — the unit appeared to be quite capricious being frequently calibrated and inaccurate. As a result, while the very first version of the device was put to the test, we put our electronic compass back on the shelf; professional divers make sure to always dive with a mechanical compass, azimuth heading problem was solved.

The picture depicts one of the options — the navigation receiver is fixed to the diving panel together with a mechanical compass:

And this is what the first version navigation receiver looked like:

It wasn’t what we call efficient — there were problems with the reliability of the reception (a small antenna mounted on the device), having rapidly followed by version 2, shown in the first picture.

Initially, there were two different solutions: robot-based (ROV/AUV) and human-based. The robotic option looks like a cylinder on the cable, coated with polyurethane. All electronics of the navigator is inside the receiving antenna, for this space arrangement we got the first patent of ours. And that’s what was functioning alright — this option worked as had been planned. Here it is, yellowish, in the photo:

As for the diver’s option, it wouldn’t work without problems — lower sensitivity, bigger mistakes, loss of reception. A bunch of tests, simulations and experiments let us comprehend it’s all about where you place it — a small piezo-ring of the diver-based receiver (a black cylinder on the body of the navigator) used to be often shadowed by the diver.

In the end, we decided to cross the two devices — since the robot-based navigator proved to be so good at reception, it became responsible for it. The transducer-in-question can be mounted on the cylinder (on the diver’s back), on the diver’s shoulder, or it’s possible to fix it on the diving panel. The old navigator reminds us only by its “display” — the interface part made as a separate unit that can be both mounted on the panel or hand worn. Upon real-world operation, the interface, in its turn, was modified as well — with unnecessary details removed and important parameters made larger.

That’s how it looks like in the hands of a real diver:

The navigational buoys

Now let’s talk about the navigation buoys, which provide all this underwater splendor. As it has been mentioned above, the navigation buoy is a thing which receives GNSS signal and retransmits it into the water.

The first version of buoys looked like this:

When in use, they proved to have a number of annoying shortcomings, the most embarrassing of which was associated with frequent “flowing” into the buoy.

Flowings cause test and works interruption and the user’s dissatisfaction, you know what I mean.

It quickly became clear that the buoys were simply pouring water in through GNSS antennas made by a Chinese manufacturer (looked like a “flasher” on the cover). The antenna used to be screwed into the lid of the buoy, but water did not flow in through the areas in which the antenna fit the buoy (we had not spared sealant and rubber), no, it did it through its own body. Out of despair, we decided to make our own antenna and hide it under the cover of the buoy, thus, having extra leakage points eliminated. It’s a new set of buoys in a case specially made for them that is presented in the picture below:

The turtle back you can see on the cover has become home for the GNSS receiver board. To top it off, a second lamp was added and we placed them both so that they shine almost horizontally — the previous arrangement variant was not seen from the water too clearly.

But it was the internal soft that had been changed the most dramatically. I’m going to present the whole evolution of the quality of the navigation data in a series of the following pictures.

Here are the results of one of the first significant tests held in the White Sea in 2015. The buoys and the receiver were “static”, the severe White Sea, challenging conditions — shallow waters and a strong multipath effect:

Another screenshot of our technological software. The very same White Sea. We were rowing with the receiver lowered on a cable.

And here’s April 2016, the Volgograd reservoir. Tre track was uploaded from diver-based receiver, that time its version was still one. The average bounce (the track width): approximately 1.5–2 meters:

From the very beginning, we made sure to stick to an open interface protocol with tracks uploadable in KML, GPX and CSV data format.. The diving devices are chargeable wirelessly and can be connected to a PC via Bluetooth. When uploaded, the track Google Earth or SAS.Planet compatible. Later on, we made a GNSS receiver emulation, so, from now on, the robot-based receiver (we called it RedNODE) can be connected directly to a PC running SAS.Planet application to use all of its conveniences: offline maps, the ability to select any layer, mapping the track in real time, etc.

And here comes the diver who helped us in April 2016 at the Volgograd Reservoir:

Please note he is wearing a navigator (the yellow one) fixed on his arm while the other one (the black one) is hanging on the scuba tank. The track from the reservoir, shown above, was uploaded from the black navigator, the second one, mounted on the cylinder. The track recorded with the hand worn navigator proved to be too bad, with a lot of gaps. It’s after this dive that we finally decided to mount the acoustic receiver so that it could not be shielded by the diver.

October 2016, the river Pichuga estuary, the Volgograd reservoir area. Two tracks captured by two devices simultaneously: RedNODE (the robot-based receiver) and RedNAV (the diver’s navigator).

We see two tracks traced from the same boat by means of two devices — RedNODE (the robotic navigator) and RedNAV (the diver’s navigator), both lowered on the rope from a rubber boat board. Performance of the devices beyond the navigation baseline(beyond the buoys shape) was being tested. The RedNODE track (in purple) was captured directly with SAS.Planet application use, the diver-based receiver track was uploaded after the fact and laid over. At Waypoint 1, the diver’s receiver was taken out from the water while the RedNODE would be kept in the water to the very the shore, which is evidenced by the track itself.

There is even a photo taken at that time:

The river Pichuga, Volgograd, October 2016

At that time, we were very surprised with the fact that the device was working at the very shore — given that we were operating under extremely difficult hydrological conditions, moreover, it was functioning beyond the navigation baseline.

And here we go with the results obtained with the latest (to date), firmware and “hard” version. The diver’s tracking data, November 2016, the Moskva channel, in the area of Vodny stadion metro station, Moscow:

I’d like to point out the extent to which the diver’s work is facilitated. The diver’s task was the following: with the help of the navigator, to dive, to get to one of the buoys, then to get to the other buoy and to get back.

The immersion conditions: murky water, visibility was less than 1-meter range. The diver exactly fit into his trace — the maximum deviation from his own route was 1.5 meters maximum! The distance between buoys 2 and 4: about 210 meters. That is, the man did not have to waste his time and efforts for the search — he was simply following the device. It should be noticed that real distance between the buoys can be as large as 700 meters (that was tested in real conditions), and the maximal range for the system is up to 3000 meters.

P.S. Who participated in the project:

- One man designed and spread all the PCBs and drew all the mechanics, he also elaborated the assembly technology, soldered it all by himself (for reference, there are more than nine hundreds soldering points in one navigator!) and assembled everything;

- Another man came up with the model and developed all the firmware (as well as assisted in assembling);

- Yet another man managed all of this, while directing the research which would get stuck from time to time and seeking places and people for testing, as well as touring with the demo kit and pestering miscellaneous funds.