Underwater Navigation Device

[reefduffer]

...
The problem with inertial units, without gps, is no way to effectively account for ocean currents..which could mean hundreds of yards, to miles in just an hour long dive, depending on where you are diving.

I don't think that's the case. What inertial units do is doubly integrate the instantaneous acceleration (all they can sense) over time to derive velocity and then distance. Newton's laws of motion apply: d = 1/2 * a * t**2, simplifying for 0 initial distance and velocity. Currents may be substantial, but they can't move the diver in space without accelerating him at some point, even if that's one big pulse - or velocity step function - when he jumps in the water. The unit will sense that initial acceleration caused by the current, and any subsequent changes, and that ought to be enough. It doesn't matter what causes the acceleration, and there is no motion not caused by acceleration.

The problems are that the tiny errors or noise in the acceleration sensing of reasonably available real-world sensors, integrated twice to calculate velocity and then distance, over an hour or so, result in unacceptable final errors in calculated distance. Other complexities and sources of error are that the problem needs to be solved in three dimensions (or maybe 2.5 for the diver problem), with instantaneous orientation of the acceleration sensors also an unknown that must be derived from that same acceleration data, perhaps aided by an electronic compass, depth sensor, or whatever other cleverness can be thought of - but those compass etc. sensors also have errors and noise. The report of the study emoreira pointed to a few posts above is some pretty good reading on this.

[The above wouldn't be the case for the 'pedometer' approach, like the Honeywell Dead Reckoning unit, one of several reasons why that doesn't translate very well to diving, e,g, sensing fin strokes. That doesn't work on land, either, if the unit rides in a car].

And then there is always the Radar reflective Flag, that any diver could hold up with a speargun or on a good safety sausage--all the boat would need is simple radar and a Garmin chart plotter..

It takes quite a flag to actually be effective. See http://www.scubaboard.com/forums/re...3968-radar-reflective-smb-safety-sausage.html

 

[reefduffer]

As I said I would, after there was no activity in the DEMA '13 time frame, in early December '13 I refreshed my inquiry to Navimate about the state of this project. I was pleased to get this response today:

=============================
... The delays are unfortunate, but as you
say, not unusual for this type of state of the art product. We have added
more engineering staff, and are now pursuing this more actively than during
part of the last two years, when we concentrated on other, non diving
related development work. The first of our patents for the Navimate system
was just issued, which is an important milestone.

We expect to be seriously testing working hardware later this year, and will
begin retails sales as soon thereafter as possible.

The functionality has not changed, though we have of course refined our
ideas for how it should work over the time we have been doing development.

Please feel free to post this information, and I apologize for the delay in
answering.

- Barry

Dr. Barry Megdal

Navimate - a product of Shb Instruments, Inc.
19215 Parthenia St., Suite A
Northridge, CA 91324
Navimate - GPS for Divers
(818) 773-2000 (818) 773-2005 fax
bmegdal@navimate.com

Dept. of Electrical Engineering
California Institute of Technology
Pasadena, CA
bmegdal@caltech (use either email)

===============================
I looked and noticed no update on the website (see above) but I'll probably keep looking a little more frequently for awhile.

I took a quick look for the patent he referenced, but didn't find it using the obvious criteria. But he says it "was just issued", and the USPO online database sometimes takes a little while to catch up. I'll keep checking there as well.

 

[Lorenzoid]

As I said I would, after there was no activity in the DEMA '13 time frame, in early December '13 I refreshed my inquiry to Navimate about the state of this project. I was pleased to get this response today:
. . .
I took a quick look for the patent he referenced, but didn't find it using the obvious criteria. But he says it "was just issued", and the USPO online database sometimes takes a little while to catch up. I'll keep checking there as well.

I couldn't find an issued patent, either, but this looks like it might be his patent application:

http://www.pat2pdf.org/patents/pat20110141853.pdf

 

[reefduffer]

... Maybe that will improve, and/or a scuba product could use something a little pricier with a little less error. But the problem is that the state of the art for inexpensive accelerometer/gyro sensor tech is pretty darn good for most uses, so there's less pressure to get more accuracy in consumer sensor tech. I think there's another conceptual breakthrough needed, or some other application like gaming input that drives more accurate sensors, or this will be a long time coming to general scuba.

I was just poking around the web doing some reading, and found this: Micro-Technology for Positioning, Navigation and Timing (Micro-PNT)
DARPA is funding some very serious research into technologies that might make this happen:

"... to develop technology for self-contained, chip-scale inertial navigation and precision guidance for munitions as well as mounted or dismounted soldiers. ... development of a single package containing all of the necessary devices (clocks, accelerometers, and gyroscopes) incorporated into a small (8 mm³) low-power (1 W) timing and inertial measurement unit. On-chip calibration should enable periodic internal error correction to reduce drift and thereby enable more accurate devices. Trending away from ultra-low drift sensors towards self-calibrating devices will allow revolutionary breakthroughs in PNT technology..."

There's a good deal more, not a lot of quantitative details, but some. Enough to suggest to me that if realized it could plausibly meet the "under the boat after an hour" benchmark. Still R&D, and military. But when GPS was first being developed, also as military tech, it wasn't anticipated we'd all carry one in our phones. It will trickle down. Not soon.

 

[reefduffer]

I couldn't find an issued patent, either, but this looks like it might be his patent application:

PAT2PDF - Free PDF copies of patents: Download and print!

Yup. Issued Feb 18, Patent # 8,654,610
Patent US8654610 - Underwater acoustic navigation systems and methods - Google Patents
Looks the same as the application you linked to.

Nothing new on the website AFAICT.

 

[emoreira]

An Inertial Navigation System (INS) would be adequate for dives from a boat or shore, where the goal is to return to the boat stairs/shore after an hour diving.
I think that there should be no need for such a device in caves, wrecks and drift dives. In a cave the diver should follow the life line. In a wreck the diver should follow the wreck silhouette or the life line if penetrated. In a drift dive, normally the boat will follow the diver's bubbles to pick them up at the end of the dive, as, if the current is strong enough, the divers could not return to the boat owing to the strong current. I do not mean a soft current (less than a knot), where the divers should swim against the current in the beginning of the dive and dive with the flow in the return.
As any piece of gear, it's useful in certain conditions and useless in others.

---------- Post added March 28th, 2014 at 09:55 AM ----------

Yup. Issued Feb 18, Patent # 8,654,610
Patent US8654610 - Underwater acoustic navigation systems and methods - Google Patents
Looks the same as the application you linked to.

Nothing new on the website AFAICT.

ABSTRACT
An acoustic underwater navigation system is disclosed. For instance, an underwater receiver determines its position using signals broadcast from an array of acoustic transmitters located near the surface. The position of the array is measured using global positioning system (GPS) technology and the transmitters collectively produce an acoustic signal in which the position and attitude of the array and the GPS time of transmission are encoded. An underwater receiver which is synchronized with the GPS time uses the transmitted position and attitude of the array and the transmission time information to calculate its position.


The description of the device patented seems not to be an Inertial Navigation System, but something like a pinguer in the surface and a diver's receiver.

 

[reefduffer]

The description of the device patented seems not to be an Inertial Navigation System, but something like a pinguer in the surface and a diver's receiver.

Yes, there is most definitely a relatively small array of acoustic transmitters a little below the surface, cabled to a GPS receiver and some other sensors and computers above, on a buoy or boat etc. Clumsier and just harder to do in real diving on a boat you don't control, but not much worse in that regard than the Desert Star gear, and with the promise of a lot more information available to the diver, and possibly the boat and other divers, the DM, etc.

Inertial is the solution we want. It's clear the technology isn't there yet, even for the military, and won't be for at least a few more years. Like a lot of other gear we'd like to have in our diving that are currently "sci fi" but not impossible, we'll just have to wait and dream.

In the meantime, in some situations, the Navimate (if and when it actually becomes available) solves the problem, even if it's a bit clumsy on the boat end. If a dive op installed one of these beacons on his boat and rented the diver unit, I would certainly pay a reasonable charge in some dive environments. Not so much in others.

This thread has for several years been discussing both inertial and beacon-based navigation for divers; what's common is the problem, not the technology.

 

[DesertStarDivetracker]

I have an underwater acoustic navigation system set. It's very simple to use and quite handy. Takes regular batteries (transmitter takes AA; receiver takes 9V). The receiver lets you know by LED lights the distance you are away from the transmitter; not exactly a GPS unit per se; it will lead you to wherever you decide to place the transmitter, though. You could also have multiple transmitters in different locations, with different pinger speeds. So you can have one transmitter at one site with a slow ping and another transmitter at another location with a faster ping so you would be able to differentiate between the two, or more if you want to get "crazy."

I'm quite pleased with this unit and hasn't failed me. It's called the Divetracker Sport, and I recommend you check it out if you have any trouble finding your way back to the boat or given location. Good luck with your lone dives, though I would recommend you always dive with a buddy, I'm a big fanatic on safety: "Safety first!"

 

[Mike.D]

I don't think any underwater nav device is a good substitute for situational awareness, nav and buddy skills.
A compass does the same thing although a little more thought is required than blinking red lights.

 

[emoreira]

I don't think any underwater nav device is a good substitute for situational awareness, nav and buddy skills.
A compass does the same thing although a little more thought is required than blinking red lights.

I agree with your statement, however having a means to return to the entry point without spending part of your attention to the navigation and compass, makes me (at least me) enjoy better the dive, as I don't have to track the heading and deviation.