mapping systems

[smartbomb]

greetings all,

just joined. as for my background, i was a padi owsi in the 90's until i burned out. teaching in north florida in the 90's was a wild ride. during that time the shop in tallahassee i worked for arranged a cave 1 class taught by a guy who was a legend. unfortunately he perished in a system in wakulla county. at that time i bailed rationalizing, if it can happen to him, it could happen to me. still cave diving intrigues me to this day.

add to this i am a licensed surveyor/mapper. my background here is almost exclusive to remote sensing, including high precision gps, lidar, some radar and now getting into sonar. i am strong in to sensor integration and application developement with respect to surveying/mapping instrumentation.

what i have been toying with for the past few months is a towed/self propelled 360 degree (on the horizontal axis) multibeam echo sounder. my application is for scour mapping at bridge piers but has a strong cross over into cave mapping. there are tons of issues to resolve, cost being the greatest. the biggest challenge in the overhead environment is the lack of positional updates that surface systems employ(gps nmea to the mbes).

the question i have for ya'll is what level of precision/accuracy does the typical cave map need. how critical is the linear distances traveled (+/- 1', .5'). these are generic questions and the search function is my friend.

who knows, this project could be the catalyst to get signed up for cave 1 again.

cheers
scot

[rchrds]

Very interesting work- if you have questions on how to integrate your sensor, or for an example of a system that worked pretty well (fairly well, depending on which side of the data integration you were on) you might consider talking to Bill Stone or Barb Am Ende, if you have not already- Of course Bill built a similar machine for the Wakulla II project, and I believe that Barb did most of the number crunching after the dives. I believe that most of the linear positioning was solved with a combination of multiple INS modules, backed up with periodic radio location stations, whose stations were found from the surface using a ULF beacon. I also understand that the INS suffered from significant drift, I am sure due to the low rates of angular change inherent to being mounted on a scooter in large passage. Anyway-
To answer your last question, here are the standards as far as they apply to cave mapping. The most commonly referenced standards are the BCRA (British Cave Research Association) Standards, and are as follows:

Grade 1: Sketch of low accuracy where no measurements have been made
Grade 2: May be used, if necessary, to describe a sketch that is intermediate in accuracy between Grade 1 & 3
Grade 3: A rough magnetic survey. Horizontal & vertical angles measured to ±2.5º; distances measured to ±50 cm; station position error less than 50cm.
Grade 4: May be used, if necessary, to describe a survey that fails to attain all the requirements of Grade 5 but is more accurate than a Grade 3 survey.
Grade 5: A Magnetic survey. Horizontal and vertical angles measured to ±1º; distances should be observed and recorded to the nearest centimeter and station positions identified to less than 10cm.

Underwater cave surveys, despite some claiming otherwise, are almost always grade 3 or 4 surveys. Currently the state of underwater compasses, and the difficulties with aiming and sighting them, do not allow for much higher accuracy, and certainly not on a continuous basis. In addition, the use of a depth meter for elevation, which only reads in whole feet does not allow for the required vertical accuracy to produce a grade 5 map. In a few rare cases, a grade 5 survey may be accomplished underwater, but it is highly laborious and time consuming. This becomes rapidly evident when loop closures to multiple entrances have large error values. Vertical error becomes self correcting however, as depth is always more or less absolute, whereas in dry caving your depth can continue to wander with no water surface to continuously correct from, reducing vertical loop closure errors, particularly in large loops.

Jason

[bgillespie82]

If you want to play with it in some local areas let me know.

Ben

[smartbomb]

thanks for the input.

ben at this point its vapor ware. i am at the design stage. for the scour monitoring its almost a no brainer. there is off the shelf stuff that i can tweak for either towed or submerged apps. the overhead environment is where the challenge is.

i was thinking the radio beacon strategy would be usable, wifi location or some loranesque setup. ulf ..why didn't i think of that. from a sheer surveying point of view, cave mapping has traditional surveying beat hands down in terms of fun factor. i will keep you updated as thing slowly progress.
cheers
scott

[Slüdge]

you might consider talking to ... Barb Am Ende

Barbara is Squirrel Girl on this forum.

[bgillespie82]

i will keep you updated as thing slowly progress.


Yes, please do

[BackstageDiver]

Completely out of curiosity, what kind of equipment is usually used to map caves? Is it just knotted line, compasses, and an experienced cartographer to draw the lines? Are there any high tech devices employed like intertial tracking, sonar, lidar, etc? Somewhere in between?

[FW]

One way to get positional updates, and loop closure is using "cave locators" (aka pingers). They send a low frequency radio signal through the limestone, and then you can locate the position from above. I have heard of accuracy of a few centimeters.

[mpoucher]

Something that could be used in conjunction with traditional surveying might be useful. The most difficult information to obtain is accurate passage dimensions. Something that could be run through a passage and have marks at known stations would be useful for collecting sidewall and correlating it back to a traditional compass and tape/knotted line survey.

In particular it would very useful in some of the dark water caves.

[smartbomb]

what i envisions differs from the original application where 180 degree scan would suffice for mapping pier scour and could be pulled off with a multibeam and side scan sonar.

the basic design is a ring of 6 transducers to cover a 360 sweep about the centerline axis with ins/imu, depth, direction and position (releative would work and is the most difficult subsurface). each sounder is capable of 50-200HZ or pulses per second. in theory as you advance in the cave, the ring will generate a 360 scan along the path traveled.

ins/imu drift is the enemy. we have the same drift issues with the ins/imu in our airborne mapping system and a typical hydrographic operation. here the major advantage is the ability to minimize the imu drift by a series of jinks or turns and to use gps to provide periodic updates to the IMU in order to correct for accelerometer and gyro drifts.

with traditioanl lidar/hydro/sar, the imu/ins data is used to smooth/fill gaps between the gps position of the vehicle and the exposures(images, laser point, radar reflection at time x) during times of no gps obsrvations. given the overhead environment, there are no positional data (gps) to help steer the imu/ins. the setup now becomes a system where the navigation is derive stricly by angles provided by a "drifting" imu/ins. it doesn't take very long before the drift creates large errors in the positions. the trick will be developing a means to provide additional RELIABLE positioning underwater, in the overhead confinement of a cave system. in the previously mentioned system, radio beacon data was available and may be the only alternative.

my head is starting to spin! i have really created a mind twister; open cranium insert worms

[apitkin]

Mike's right. Traditional survey techniques are satisfactory for a basic line plot, especially when augmented by radiolocation devices like Ken Smith's 'pingers'. What we need is a device that will scan all the passage walls at a point selected by the surveyor and then save that data in internal memory for later downloading.

As it happens, there is already a device that has most of the components of your system and has the ability to receive data from external devices via infra-red, so a sonar system could in theory be added on. What's more, it goes underwater. It's called the Liquivision X1. And it doesn't have to run decompression software...

Just a thought.

Andy

[Squirrel Girl]

Barbara is Squirrel Girl on this forum.

Thanks Russell. Work is on overdrive right now, so I'm not in a position to give a coherent answer. Hah, too many sensor problems to deal with that I'm tied to with a ball and chain.

[smartbomb]

given the work i do, i have access to many manufactures of survey equipment. i have some feelers out to see if i can drum some manufacturer support. fingers crossed.

[Squirrel Girl]

They had some interesting talks at the Intl Congress of Speleology this year. Check out the proceedings at the Geophysics symposium. They had some GPS tracking of a guy in a dry cave. Then SWRI had hampster balls with sensors that they dumped into fractures, perhaps smaller than people that would float down the water.

[rchrds]

I am with mpoucher, some sort of discrete single output sensor is desperately needed to gather sidewall range information. In dry survey the disto has come into heavy use, and is very popular for this- one laser range, and with the addition of the disto-x, an azimuth and elevation to boot- all downloadable into a palm device, which plots it as you go. There is no good tool for reliably sensing ranges underwater- particularly if you are shooting down a narrow crevice to get a feel for the back- the sensors that are available are just too wide ranging, and typically give inaccurate responses (think flashlight compared to a laser.)

As for INS drift- since you can now use GPS to mitigate drift by integrating your GPS signal, which basically consists of correlating multiple signals into one discrete position, how about setting up a network of ULF emitters on the surface above the cave, which transmit on a periodic basis, and are georeferenced to whatever accuracy you need (and though accuracy of a few centimeters may be possibly between transmitter and receiver, the geolocation is typically less accurate than that.) Then collect and triangulate your position using the multiple ULF signals, and use that data in place of the GPS data to keep your drift under control.

WAY more math than I am prepared or capable of doing, but it is an idea.

Jason

P.S.- if you can come up with a single output ranging device (emitter in the front, OLED display of range on the back) in the $250 range, you will sell a whole bunch of them- I can guarontee!!

[rchrds]

Okay, brain is working today- here is an expanded example of how you could use the ULF beacons to replace GPS signals. Assuming you use a set number of beacons, and assuming that the beacons can be received off axis a certain distance (they can, but not sure how far, I haven't actually used one) and Assuming that you have georeferenced the beacons on the surface to a pretty precise position (handheld GPS will NOT suffice- either surface survey with a theodolite, or a precision GPS.)

The location is all based on the timing of the signals, similar to how GPS is calculated. ULF has a very long, low frequency wave, which makes things a little messier. But, unlike GPS, you will not be travelling fast, so updates can be in numbers of seconds, rather than miliseconds.

Assume a sinuous path in the cave. For my example, we will have three locator beacons. Each beacon is set to transmit a discreet signal- for simplicity, beacon 1 (ULF1) sends a dot-dot signal. beacon 2 (ULF2) sends a dash dot signal. Beacon 3 (ULF3) sends a dash dash signal. Each beacon signal is timed so that the terminus of the second element ends at a certain time, and the downturn of that signal is the actual time that the mobile mapper will use for calculation. Obviously, I am making an analog example that can be transferred to a digital signal, but again, not sure what the capabilities of the ULF beacons are. The signals of the ULF beacons are timed using the first (timing) block of GPS data, accurate to 10 miliseconds with good signal. The end of the transmitted signal occurs at a set known time, based on GPS time, which will be the same for all emitters, and can be continuously clocked using the GPS signal.

You set ULF1 so that its signal ends at the end of one second, ULF2 ends at 3 seconds, and ULF3 ends at 5 seconds. If the range involved is such that this is not enough time for each signal to arrive at the receiver separately, increase the times. (Not going to do the math right now.)

The whole point of making discrete timed signals, is that this allows you to have only one receiver on the mapper, as well as use only one frequency on the transmitters. Unlike a GPS, where you can squeeze 14 independent receivers on one chip thanks to high consumer demand, I'm sure you will be space constrained to be able to add multiple ULF receivers.

Now, in your processor, you build a table (or do running calculations) that calculate the distance from each beacon using the delay in the signal from each beacon, as you know exactly what time (within 10 miliseconds) that the signal was sent. In truth, having separate coded signals from each beacon is probably unnecessary, but it would help if you had to listen to them manually (analog) to determine if they were all working or something.) In addition, it allows your program to log each signal, in case some were missing.

Now that you have the distance from each beacon, you can easily triangulate your position in 3 dimensions. (creating a sphere from each beacon.) Now, of course, mathematically this provides you with, um...9 positions? but you can throw out the unlikely ones by factoring in your digital depth with some slop built in (the digital depth should be less accurate.)

I think that at this point, most of the parts required for the mapper side are available and easy to set up, as they have been used in other products. However, as ULF signal work is a pretty tightly held regimen between unauthorized users (cavers) and the FCC/US Navy/NOAA there might be a shortfall on the transmitter side- as I'm not sure what advances have been made in this field in the last few years on our (caver) side. This is something you will have to take up with the various guys that have been building them, but I doubt it is a large step, if this is your field of work.

Good luck.

jason

P.s.- also on your original block diagram, in addition to the compass you will need some measure of vertical axis- you must think 3D, not on a flat plane, if your sensor ring is canted in any direction, this will supremely effect where the results of your signals are located- the compass (horizontal axis) and elevation (vertical axis) must be integrated, and you cant expect to keep the sensor ring level with a bubble level or something- not while diving.

[rchrds]

Mike's right. Traditional survey techniques are satisfactory for a basic line plot, especially when augmented by radiolocation devices like Ken Smith's 'pingers'.
This is certainly a matter of opinion- and relates directly to the end use of the data- for paper maps used for navigation, I would agree. For volumetric calculation, for example, that is definitely not the case.



As it happens, there is already a device that has most of the components of your system and has the ability to receive data from external devices via infra-red, so a sonar system could in theory be added on. What's more, it goes underwater. It's called the Liquivision X1. And it doesn't have to run decompression software...
Andy

Andy is correct- this could very well act as a base module, providing a compass (possibly not accurate enough, and limited in vertical axis measurements, I will find out next month) a digital depth measurement, and a processor. Whether or not the processor is up to what you are going to ask of it is another discussion. Of course, you would have to integrate an additional module (ala the X-Link) that would receive and process ULF signals, add a 3rd accelerometer for measuring vertical angle, and then some way of transmitting your data from the mapper to the unit.

Probably this makes little sense to have it all separated and be forced to integrate multiple data transmission links rather than to have it all located on one board, with the calculations made in a single processor and program, and all of the data transmission hardwired.

Jason

[FW]

Hey BobK, are you reading all this?

Smartbomb, did you read the other thread about this? (High tech survey equip?) Maybe y'all should work together.

[BobK]

I've been looking at this on and off for a couple of years. I currently know how to build a system that can survey a cave with accuracy to within a foot or so. There is a slight cost issue :-) If I could get a hundred investors, putting in around 1K each, I could build it.

Otherwise we have to wait until the electronics get better, or do the pinger thing.

[BobK]

As for INS drift- since you can now use GPS to mitigate drift by integrating your GPS signal, which basically consists of correlating multiple signals into one discrete position, how about setting up a network of ULF emitters on the surface above the cave, which transmit on a periodic basis, and are georeferenced to whatever accuracy you need (and though accuracy of a few centimeters may be possibly between transmitter and receiver, the geolocation is typically less accurate than that.) Then collect and triangulate your position using the multiple ULF signals, and use that data in place of the GPS data to keep your drift under control.

WAY more math than I am prepared or capable of doing, but it is an idea.

Jason


The INS drift in a low priced system is very very bad, on the order of meters in seconds. They are really designed to fill in the "curve" between 1 second GPS updates. A more accurate INS is orders of magnitude more expensive.

Other then INS, it might be possible to put together a system using ranging lasers if you had a highly accurate compass. This system would require two divers but could accurately map a system far better then the manual methods being used now, and would not require the divers to write stuff down.

[smartbomb]

rchrds (http://www.cavediver.net/forum/member.php?u=382), the ulf system you describe is very similar to a pseudolite(PL). PL's are most often small transceivers that are used to create a local, ground-based GPS alternative. the concept is the same radio based ranging. like GPS you can measure fractional parts of the carrier for super precise measurements.

hopefully i will here from some of the manufacturers that i deal with this week. maybe they have some works in progress or mothballed stuff that may apply.

anyone here associated with the WKPP? i would like the get some first hand info on the whole survey process.

this whole idea started as an exercise for surveys of bridge piers and now has completely morphed into something a whole hell of a lot more interesting. being an old fart with latent ADD is a burden i must carry. i get bored very easy and my mind tends to drift into flighty concepts.

cheers
scott

[smartbomb]

god i can't help myself. has anyone looked into close range photogrammetry? essentially, 2 cameras separated by a known distance (i.e. mounted to a bar of 1 meter) can simultaneously capture an image. with some known scale present in the images, a 3d map can be "digitized" from the images. the concept is identical to the old steroscopes you would see in old western movies. it still doesn't resolve the spatial orientation, but it is an option.

from wikipedia
USBL (Ultra-short baseline) is a method of underwater acoustic positioning. A complete USBL system consists of a transceiver, which is mounted on a pole under a ship, and a transponder/responder on the seafloor, a towfish, or on a ROV. A computer, or "topside unit", is used to calculate a position from the ranges and bearings measured by the transceiver.

An acoustic pulse is transmitted by the transceiver and detected by the subsea transponder, which replies with its own acoustic pulse. This return pulse is detected by the shipboard transceiver. The time from the transmission of the initial acoustic pulse until the reply is detected is measured by the USBL system and is converted into a range.

To calculate a subsea position, the USBL calculates both a range and an angle from the transceiver to the subsea beacon. Angles are measured by the transceiver, which contains an array of transducers. The transceiver head normally contains three or more transducers separated by a baseline of 10 cm or less. A method called “phase-differencing” within this transducer array is used to calculate the angle to the subsea transponder.

USBLs have also begun to find use in "inverted" (iUSBL) configurations, with the transceiver mounted on an autonomous underwater vehicle, and the transponder on the target. In this case, the "topside" processing happens inside the vehicle to allow it to locate the transponder for applications such as automatic docking and target tracking.

[FW]

anyone here associated with the WKPP? i would like the get some first hand info on the whole survey process.
What you really need it the "older" Wakulla group, called Wakulla 2. From what I understand, the current WKPP only uses knotted line, and a dive compass to survey, and they only survey to the nearest 10 feet. They don't record passage width at all.

[smartbomb]

i figured the wkpp only because they're local to me. anyone could shed some background on the survey process. i have 16 years of "terrestrial" surveying under my belt. mostly curious as to the cross over techniques; traverses, loop closures, control marks. if compass and line are the norm, it seems fairly straight forward. but how does the higher levels of surveying get done? at the top of the scale i read the requirement is the cm level. hell i know guys that cant pull that off on dry ground. in a nutshell "traditional" surveying is getting boring. according to my 14 y/o know-it-all, i need something with a challenge so i don't turn into dull old fart.

[Squirrel Girl]

What you really need it the "older" Wakulla group, called Wakulla 2.

http://www.usdct.org/wakulla2.php

There was a first Wakulla expedition by the USDCT. Then there was the WKPP. Then the USDCT went back for Wakulla 2. The WKPP were invited, but chose not to participate. And now it's back to being WKPP at the park again.

[Arnold Mesiser]

http://www.usdct.org/wakulla2.php

There was a first Wakulla expedition by the USDCT. Then there was the WKPP. Then the USDCT went back for Wakulla 2. The WKPP were invited, but chose not to participate. And now it's back to being WKPP at the park again.



It's amazing how much cutting edge and NEW technology was created at or for the project.I still find the dives fascinating to this day -so MUCH more was done for cave science and diving rather than simply worrying about EOL

[Webmaster]

Jason you might be able to use a ULF system like that for triangulation. But I don't think it would work too well as a GPS type setup. GPS is all based on timing, and of course the time that signal takes to travel from the satellite to the receiver is fairly constant because it's travelling through the atmosphere.

Underground it's going to be travelling through a much greater variety of materials, and even small variations would cause the position to be off.

Acoustic systems designed for open water environments are unlikely to work in a cave as-is because of all the reflections.

If you just had two devices that worked line of sight, that could talk to each other that would work. Collect depth, orientation to the other device relative to magnetic north, and range to the other device at each station. Maybe a low powered ULF transmitter/receiver that was very directional.

[apitkin]

Andy is correct- this could very well act as a base module, providing a compass (possibly not accurate enough, and limited in vertical axis measurements, I will find out next month) a digital depth measurement, and a processor. Whether or not the processor is up to what you are going to ask of it is another discussion. Of course, you would have to integrate an additional module (ala the X-Link) that would receive and process ULF signals, add a 3rd accelerometer for measuring vertical angle, and then some way of transmitting your data from the mapper to the unit.

Probably this makes little sense to have it all separated and be forced to integrate multiple data transmission links rather than to have it all located on one board, with the calculations made in a single processor and program, and all of the data transmission hardwired.

Jason

Eric at Liquivision tells me that the compass is very accurate indeed, just that the current deco software doesn't use it effectively to achieve that accuracy. The accelerometer can measure vertical angle. Also, the processor is far more powerful than (I believe) any other dive computer, which allows the use of the free GNU compiler which produces relatively slow code. I got the impression from talking to him that even using inefficient open source tools, the X1 had plenty of processing headroom when doing deco calculations. Decosoft, for example, computes two models simultaneously. And that doesn't include for the potential performance improvement using efficient compilers (=$$$, of course). I doubt that the necessary calculations for a location system would be much more processor-intensive.

I agree it's better to have it all on one board, but with the X1 you have a very compact, powerful, underwater computer with plenty of storage memory, a great screen, an accurate compass and depth gauge, and a means of hardware expansion. It might be a good place to start.

My concern about the ULF idea is based on (my understanding of) simple physics. With low frequency comes a long wavelength. That long wavelength will necessarily limit the spacial/temporal resolution of the signal, and therefore the accuracy of location. I'm not sure how low the frequency needs to be, nor how to calculate exactly what the limit of resolution will be. I haven't opened a physics textbook in a long time, so I could be completely wrong.

I hope so, because it's a great idea.

Andy

[jdz]

Hi guys, just been alerted to this thread..

I have been interested in various mapping techniques for some time.. Initially I had a ULF transmitter and receiver built very similar to Pearse's unit, but it was able to receive a surface signal once the position was located from above, hence we could move on to a subsequent point and hence gather many points on the same dive. this system was used at the same time as my collegue was using his "pinger". In this way we completed the entire resurvey of our well known Tank Cave here in OZ with nearly 8 klms of passage.
see... http://www.cavedivers.com.au/articles/thumper.htm and... http://www.cavedivers.com.au/articles/pinger.htm and... http://www.cavedivers.com.au/articles/mapping.htm

We have also continued mapping using the simple tape & measure along the line, knowing that we had fixed known points to return to.. http://www.cavedivers.com.au/articles/history.htm

From here, we have moved on to create 3D models by using meshing software and have created a model of our Piccaninnie Ponds which I'll try to add a link to in a day or so.

I am currently finishing the housing for a "disto2" http://www.buybrandtools.com/acatalog/Leica-Disto-D2.html and will be testing this in the next week or so and can report back on this also..

I always thought that I would like to built a system similar to that described above, where we could drive 3 or 4 spikes into the ground positioned around a paddock and set up an artificial underground satellite system using ULF signals and then reprogramming a gps to receive these signals and hence reference itself u/w accordingly...

and finally another idea which will be trialled soon.. one diver with a paddle or similar object in front of a 2nd diver with camera at a known approx distance and multiple photos taken say every 5 metres along the lined passageway, then "mesh" the photos together to produce wall outlines using the paddle as a reference measure, thus collating multiple data points (similar to digimapper, but much less expensive..)

anyway, enough rambling.. cheers,

JDZ

[FW]

...and finally another idea which will be trialled soon.. one diver with a paddle or similar object in front of a 2nd diver with camera at a known approx distance and multiple photos taken say every 5 metres along the lined passageway, then "mesh" the photos together to produce wall outlines using the paddle as a reference measure, thus collating multiple data points (similar to digimapper, but much less expensive..)

anyway, enough rambling.. cheers,

JDZ
That might work in very clear water. There are many caves with low visibility.

Say hello to Ken Smith for me :-)

[jdz]

That might work in very clear water. There are many caves with low visibility.

Say hello to Ken Smith for me :-)

But we only dive in crystal clear, warm water without silt... don't we?? NOT!

Ken... NP, only though if you say hi to Gene from me...

I'll see Ken soon enough... think he's just back from a little bush walk...

Cheers, JDZ

[Squirrel Girl]

But we only dive in crystal clear, warm water without silt... don't we?? NOT!
Crud! I was gettin' all ready to fly over to Oz until I read the NOT!

[jdz]

Crud! I was gettin' all ready to fly over to Oz until I read the NOT!

No No Come Come... we can give you crystal clear water, but I'm afraid we'll have to get Ken to get you a cup of tea to warm you up..if you can wait for it;-)(I hope he doesn't read this..:axe:)

[smartbomb]

i have sourced sub components solving some serious issues. the primary hangup thus far has been linear positioning along track. based on ya'lls input ulf, tape, knotted rope are methods used. ins/imu have drift issues that were previously a pain to resolve. NOT ANYMORE. recall that in an above ground world, (aerial mapping,lidar etc) imu/ins drift can be steered with GPS and the use of a kalman filter. in a submerged environment there is no GPS.

drum roll please...

I have discovered a source for a doppler navigation system that used 4 discrete doppler sounders to position itself very precisely based off bottom returns and velocity. as a bonus, this will feed position data to the kalman filter to keep the ins/imu oriented. no added need for beacon type nav aids.

add to this, during my original search for systems to monitor scour, i have found a very high precision 3d sounder that scans a 360 degree swath as you progress along track.

the liquidvision hardware looks very promising to supply depth and azimuth.

after talking to an electrical engineering friend, microcontrollers are not a problem with respect to sensor integration.

i will be working on a block level design this week to illustrate the various components.

show me the money....funding will be a major hurdle. i will be talking to some manufacturers to see if they may have some interest. fortunately, a very good friend that has just been appointed as deputy director of the national geodetic survey. i will be checking with him to see if there are any funds available through noaa.

i work for FDOT. and one major concern we have is the rapid development of sinkholes in or near road systems. to my knowledge there is no data that maps karst specifically where it intersects the roadway. any info ya'll have may provide a spark for some interest here. with this in mind, if there are data sets, maps sketches or surveys laying around, i could use them to build layers in a geographical information system (GIS) and potentially push a GIS to the WWW.

[apitkin]

I have discovered a source for a doppler navigation system that used 4 discrete doppler sounders to position itself very precisely based off bottom returns and velocity. as a bonus, this will feed position data to the kalman filter to keep the ins/imu oriented. no added need for beacon type nav aids.


That sounds very interesting. Presumably it uses ultrasound? What if it doesn't get any return signal in some directions? In some passages, such as the ones Mike is thinking of, it may only get a return from one passage wall (think large straight but very poor visibility passage), which may be close to perpendicular to the Doppler beam and therefore will not give accurate velocity information. What about moving objects in the water, such as other divers or scooters?

To beat the old-fashioned methods in the kind of environments we are talking about, this thing has to be robust in a measurement sense, as well as physically tough. I don't want to discourage you. On the contrary, I want this to work!

You might want to try some underwater cave surveying, just to get an idea of what issues you are facing. Even just a length of well-known passage in a popular cave would be useful. If you have some restrictions, flow and silt in there, even better.

Andy

[smartbomb]

You might want to try some underwater cave surveying, just to get an idea of what issues you are facing. Even just a length of well-known passage in a popular cave would be useful. If you have some restrictions, flow and silt in there, even better.

Andy

i completely agree. i can survey above ground like there's no tomorrow. underwater, in a cave is another story.

as for the doppler, heres the specs. add to this the multibeam echosounder and an ins (specs to follow)

Configuration: 4-beam Janus array
convex transducer, 30° beam angle

Bottom Velocity
Single-ping precision
Std dev at 1m/s ±0.3cm/s
Std dev at 3m/s ±0.6cm/s
Std dev at 5m/s ±0.8cm/s
Long-term accuracy ±0.4%±0.2cm/s
Minimum altitude2 1.0m above floor
Maximum altitude2 200m above floor

Velocity range3 ±10m/s
Velocity resolution 0.1cm/s
Ping rate 7Hz max

Accuracy ±0.4% ±0.2cm/s

Depth rating 3000m

Compass: ±2° @ 60° dip, 0.5g
Tilt: ±0.5° up to ±15°
Temperature: -5° to 45°C


multibeam specs

Frequency 375kHz

Number of beams 128 x 128 (16,384 total)

Maximum range*
150m (500ft)


Minimum range 1m (3ft)

Range resolution 3cm (1.2")

Update rate (ping rate) Up to 12Hz

Angular coverage 50° x 50°

Beam spacing 0.39°

Dimensions (h x w x d) 380mm x 300mm x 160mm (15" x 11.8" x 6.3")

Weight in air 22kg (44 lb)

Weight in water 12kg (26 lb)

Power consumption 3-6A at 24Vdc

Depth rating (standard) 600m (2,000ft)

Depth rating (special order) 3000m (10,000ft)

[apitkin]

i completely agree. i can survey above ground like there's no tomorrow. underwater, in a cave is another story.

as for the doppler, heres the specs. add to this the multibeam echosounder and an ins (specs to follow)

Configuration: 4-beam Janus array
convex transducer, 30° beam angle

Bottom Velocity
Single-ping precision
Std dev at 1m/s ±0.3cm/s
Std dev at 3m/s ±0.6cm/s
Std dev at 5m/s ±0.8cm/s
Long-term accuracy ±0.4%±0.2cm/s
Minimum altitude2 1.0m above floor
Maximum altitude2 200m above floor

Velocity range3 ±10m/s
Velocity resolution 0.1cm/s
Ping rate 7Hz max

Accuracy ±0.4% ±0.2cm/s

Depth rating 3000m

Compass: ±2° @ 60° dip, 0.5g
Tilt: ±0.5° up to ±15°
Temperature: -5° to 45°C


multibeam specs

Frequency 375kHz

Number of beams 128 x 128 (16,384 total)

Maximum range*
150m (500ft)


Minimum range 1m (3ft)

Range resolution 3cm (1.2")

Update rate (ping rate) Up to 12Hz

Angular coverage 50° x 50°

Beam spacing 0.39°

Dimensions (h x w x d) 380mm x 300mm x 160mm (15" x 11.8" x 6.3")

Weight in air 22kg (44 lb)

Weight in water 12kg (26 lb)

Power consumption 3-6A at 24Vdc

Depth rating (standard) 600m (2,000ft)

Depth rating (special order) 3000m (10,000ft)

The minimum range of 1m of the Doppler system might be a problem - if at any point it cannot generate accurate velocity data then does it lose its position in the water?

And with those dimensions and power requirements of the multibeam array, it's going to have to be housed in some form of super-scooter, like Bill Stone built for Wakulla 2.

Starting to look very complex and expensive.

How about a system using just the multi-array, mounted on (e.g the front of) a scooter which could take a snapshot of the passage walls and store it when the diver operates a switch? That would help a lot with the dark water problem, even if we still needed compass and knotted line/tape methods for the basic line plot.

[rchrds]

3-6A at 24V? Uhhh that could be a problem. That's a lot of battery volume for something you have to haul through the cave. x2 on the 1m minimum, though you just have to tailor it for the larger caves- with that much battery, you wont be shoving it through anything really small anyway.
And 26 lbs in the water? Man- not looking good.

Jason

[smartbomb]

yep i see what you mean. too much weight, battery and the cost keeps going up. back to the drawing board.

what would be a ideal footprint? 20# and smaller than a single 80?

[FW]

In the water, it needs to be neutral, or at least have flotation to make it neutral. The smaller the better, but the size of an 80 would be manageable.

[KenSmith]

Hi All,

Thanks for mentioning the pingers FW. These are submersible radiolocation transmitters that are small and easy to carry. I reckon the accuracy is better than about 3% relative. So if the pinger is 100ft below your feet the horizontal location accuracy should be better than about 3ft.

The range is better than 300 ft if you are well away from any mains power lines. Mains interference can limit the range to 100 ft or less depending on proximity of power lines.

I apologise for calling these things pingers. They are not a sonar device. Location is done by a the dipole magnetic field that they generate. Pingers just sounded like a nice name and it stuck.

You can see details at;

http://kendiver.googlepages.com/pinger

As JDZ said I am going to have a nice cup of tea and some fruit cake now.

Ken

[rchrds]

Ken, thanks for posting your link! I think even my retarded ass can build one of these. I am going to try. Thanks for doing all the brain work.

Jason

[smartbomb]

ditto,

this is one of the coolest things i've seen in a while

[apitkin]

If anyone comes up with a US source for the mumetal strips that Ken used then please post it here. That seems to be the hardest component to source.

Thanks.

Andy

[KenSmith]

Hi All,

Yes the mumetal is hard to get. The mumetal I comes on a roll and is about half an inch (12.5mm) wide and 2 thousands of an inch (0.05mm) thick. It is annealed , which I believe increases the magenetic permeability. It is coated with a thin lacquer insulation, called "inlac", which insulates the layers in the core.

I believe that the thin laminations results in low loss and a high resonant Q. This is helpful for both the transmitter an the receiver. I don't think thicker laminations would be as good. Ferrite may be an alternative core material, but the permeability may not be as high. I would like to find some big ferrite rods to try. Say 3/4 inch diameter by 12 inches long.

I may have a source of mumetal in Europe so I will keep hunting.

If anyone can find a source of thin annealed mumetal in the USA that would be great. This type of mumetal is used in magnetic probes used for geophysical purposes.

Ken

[KenSmith]

I meant to say that there is nothing special about my electronics. It was my first attempt and it worked, so I haven't upgraded it.

Improvements would be a crystal locked transmitter. And an automatic turn off after say 4 hours. The Pinger could then be turned back on underwater with a tilt switch (say) when it is moved to a new location. The pinger could then stay in the cave for several days without the need to repalce batteries.

The receiver circuit would benefit from some improved signal filtering.

...I just need to spend less time diving and more time at the workbench.

Ken

[FW]

I am currently finishing the housing for a "disto2" http://www.buybrandtools.com/acatalog/Leica-Disto-D2.html and will be testing this in the next week or so and can report back on this also.
Anything to report on the Disto in a housing? I was wondering how it would do with the reduction in speed of light in water, back scatter, beam spread, etc.

[Squirrel Girl]

...I just need to spend less time diving and more time at the workbench.

Ken

Oh, the problems some people have!

[jdz]

Anything to report on the Disto in a housing? I was wondering how it would do with the reduction in speed of light in water, back scatter, beam spread, etc.

Stay tuned.. I will report back as soon as I can test, and with photos...

Cheers, JDZ

[FW]

Stay tuned.. I will report back as soon as I can test, and with photos...

Cheers, JDZ
Good luck mate, it would be great if you can get it to work.

[rchrds]

If the disto in a housing works, I will give up traditional underwater methods altogether and us my Disto-X. I would be VERY interested to hear what the results of that will be, though I can't imagine that it will be good what with backscatter and all.

Jason

[jdz]

almost there... working on too many simultaneous projects...

will report back shortly...

cheers, JDZ

[FW]

Looks nice, can't wait for your test results. I suspect you will need to take a few readings compared to a tape, and come up with a conversion factor.

[Squirrel Girl]

Looks nice, can't wait for your test results. I suspect you will need to take a few readings compared to a tape, and come up with a conversion factor.

Most people would consider a Leica to be more accurate than a tape. I've never heard of anyone converting their Disto values in a dry cave.

The plastic of the housing could, conceivably, distort the readings, then I'd just compare the housed versus unhoused Disto readings.
:smt102

[FW]

Most people would consider a Leica to be more accurate than a tape. I've never heard of anyone converting their Disto values in a dry cave.

The plastic of the housing could, conceivably, distort the readings, then I'd just compare the housed versus unhoused Disto readings.
:smt102
It is more like the water will change the speed, and thus the timing of the echos. Hopefully it will be linear. I am not to sure that the diffraction won't big a big issue, too.

[Squirrel Girl]

It is more like the water will change the speed, and thus the timing of the echos. Hopefully it will be linear. I am not to sure that the diffraction won't big a big issue, too.
Good point. But do you usually use a tape to survey? I thought most people used knotted line? If I weren't desperately behind at work right now, I'd zip out the calculations. But I'll bet in the distances we see in caves, the change in speed would be in the noise.

[FW]

Good point. But do you usually use a tape to survey? I thought most people used knotted line? If I weren't desperately behind at work right now, I'd zip out the calculations. But I'll bet in the distances we see in caves, the change in speed would be in the noise.
For rough surveys, we use knots, but for the fancy maps of clear FL caves, they use tape.

[Squirrel Girl]

For rough surveys, we use knots, but for the fancy maps of clear FL caves, they use tape.
Which ones? Enquiring minds want to know! :)

[Arnold Mesiser]

For Crappier vis Canadian caves they use tapes too :)

[rchrds]

All crappy and non-crappy Tn caves get taped as well.

J

[FW]

Which ones? Enquiring minds want to know! :)
Everything Mike Poucher maps is done with tape.

[FW]

All crappy and non-crappy Tn caves get taped as well.

J
Underwater as well?

[sskasser]

In our survey class this weekend, we did some examples with knotted line, then tape. It was pretty amazing how wide the variance could get. Of course, some people are better at estimating partial knot spans than others. I was definitely sold on the benefits of tape (with decimal values!).

Now who's got some cave they need me to survey? :smt081

[FW]

In our survey class this weekend, we did some examples with knotted line, then tape. It was pretty amazing how wide the variance could get. Of course, some people are better at estimating partial knot spans than others. I was definitely sold on the benefits of tape (with decimal values!).

Now who's got some cave they need me to survey? :smt081
Come to the TAG Fall Cave In, we will be laying line then :-D

[sskasser]

Come to the TAG Fall Cave In, we will be laying line then :-D


Sure! Swing by on your way and pick me up? :D

[rchrds]

Underwater as well?

If it is not the initial guestimation, yes. Guy James was taped. Blue Springs Resurgence was taped.

[mpoucher]

Everything Mike Poucher maps is done with tape.

I tape the main passages and other passage as much as I can, but the farther out or smaller it gets, I'm likely to use knotted line. It's a trade off in accuracy versus time.

[Brian Kakuk]

Any further progress with the Disto in the housing? I just got a huge survey job (about 9 miles) added to my duties with the National Museum and I think that device would REALLY help. Right now it's all fiberglass tape, but if this device works well underwater, it would make the project go much faster.

One question I have concerning the laser is that the first color to be absorbed by water is red. If this is a red laser, does that mean that the light returning to the device would be drastically reduced the longer the distance? We will be measuring distances of nearly 200 feet. Would this be too much for this device? Any advice would be helpful. Thanks.

Safe diving,
Brian

[Webmaster]

Those use UV lasers at 635nm which should be about the ideal wavelength to penetrate water. It looks like the maximum ideal penetration at that wavelength is about 100m.

Of course it's measuring a reflected beam so the the maximum distance measured should be at most be half that.

Add in attenuation over that distance which appears to be about 4 orders of magnitude greater than in air if I'm reading that right, and it doesn't look like it might work over a very long distance.

[phillip1]

OK this is way too technical for me but what you are saying is; there could be a device the size of beer can more or less that you would turn on at the start of a dive and it would actually map out the cave automatically for you as you swim, you then only need to download that info and you have a precise map?
If so I want one, how much?

[aainslie]

In our survey class this weekend, we did some examples with knotted line, then tape. It was pretty amazing how wide the variance could get. Of course, some people are better at estimating partial knot spans than others. I was definitely sold on the benefits of tape (with decimal values!).

Now who's got some cave they need me to survey? :smt081

How serious are you on that, Shirley?

I know a 200 ft deep cave with restricted access and 6 ft vis that I'd love to get better survey data for... and there's going, unlined cave if you're in an exploratory mode, just 1000 ft from the entrance...

[sskasser]

How serious are you on that, Shirley?

I know a 200 ft deep cave with restricted access and 6 ft vis that I'd love to get better survey data for... and there's going, unlined cave if you're in an exploratory mode, just 1000 ft from the entrance...

Very, let's talk ;) I'll be at the conference in Gainesville next month.