Just a quick post to say that the underwater Disto didn’t work quite as intended, I made a number of trips to Sump 9 in Porth Yr Ogof this summer with the aim of surveying it accurately. The water is usually crystal clear on entry to this sump however the laser was not able to read the short distances I had hoped it would. For shots that should have been 1 to 2 m in length it was just returning valves of around 0.15 m every time, the bearings will be useful but I need to return and measure the lengths traditionally.
Underwater DistoX2 Housing
I will start by saying that this idea has been copied from other cavers/ divers, this isn’t the the first time someone has wanted to use a Distox2 underwater. My reason for wanting a waterproof Distox2 is allow me to use the same methodology for underwater photogrammetry geo-referencing that I use for above water photogrammetry geo-referencing to preserve accuracy through sumps. Lasers do have limitations underwater, light is attenuated by water quite readily especially red light or red lasers. so the range is going to be very limited even in very clear waters.
The main body of the housing is made from Acetal, a small cut out sealed with an o ring allows the laser to emit and receive through the front of the box and is covered by 5 mm thick perspex. The lid is 12 mm thick polycarbonate and houses two brass buttons sealed with o rings to actuate the on/ off buttons. The springs have been taken from a Gopro housing and are the most ferrous part, making the bearing swing by 0.2° when they are swept close to the Distox2, all screws are brass. A standoff is fitted to the rear to extend the rear reference point to make it easier to align to the survey station. The gland sticking out the side doesn’t have a function other than to seal the hole present in the side ( the boxes previous life was a waterproof box for an Arduino Mega).
Due to the difference in refractive index of water and air the distance readings taken underwater are no longer correct when compared to the same measurements taken in air. The refractive index of air is around 1.00 and approximately 1.33 in the water I would be using the device in.
To prove this I made a test in my bath, I put two pencil marks at either ends of my bath, with the Distox2 in the housing I made a measurement with the marks and device underwater then again with the water drained, I also measured with a tape measure for a sanity check.
The tape read 1.415 m, the dry Distox2 in the box read 1.31 m and the wet shot read 1.70 m.
The distance from the rear of the disto to the reference extension stick needs to be added which is an extra distance of 0.109 m, this added to 1.31 m gives 1.419 m which is very close to the taped measurement.
Converting the underwater shots distance requires the offset from the front of the device to the rear to be subtracted first as this is a fixed offset added by the Disto and doesn’t need to be scaled from water to air. There is also around 0.02 m of air in front of the disto before the laser passes through the housing lense and into the water and this doesn’t need to be scaled either, i’m purposefully ignoring the 5 mm of perspex as this is very small compared to the distance of the shots being taken and probably only accounts for a few millimeters of difference.
So starting with the wet shot distance of 1.70 m we need to subtract 0.134 m which is the length of the disto plus the air gap in front. This gives 1.566 m, which we need to scale by the refractive index of water 1.33, which gives 1.177 m. To this we need to add the length of the disto plus air gap and the extension distance so 1.177 + 0.134 + 0.109 + 1.420 m which is very close to the taped distance and the dry measured distance – Result !
The distoX2 manual available here:
Click to access DistoX2_UserManual.pdf
It states that the wavelength of the laser is 635 nm, using this calculator here we can confirm the refractive index of water is around 1.33xx.
https://www.staff.tugraz.at/manfred.kriechbaum/xitami/java/H2Orindex.html
The next phase is some pressure/ wet testing of the housing without the Disto installed in case it leaks then I can begin to put it into use, sump 9 in Porth Yr Ogof is the first place I have in mind for it so that data collected in Parker Series can be accurately aligned to the rest of the cave.
Downwards at Rickford
A few friends have been working at Rickford Rising removing large boulders and making progress downwards from where the previous protagonist left off some years ago. I have always fancied a dive here but had never got round to it for various reasons. It usually has good visibility so I thought I would attempt to create an accurate photogrammetry model of the site as a snap shot of progress at this point in time, and hope to go back and update the model as progress towards the Burrington Master Cave is made !
A video has been put together by the digging team and gives a rough overview of the site:
I made four short dives on my visit, facing head first slowly filming the descent from surface to dig face allowing sufficient time for the visibility to clear each time and a survey dive (after having planted the yellow builders square on the first dive).
The builders square was used to provide a scale reference (the lipped edge is 12″ or 0.31m long) and also to provide a fixed straight edge along which I could repeatedly align the edge of my survey box with to make foresights and backsights against to allow the model to be orientated correctly. Accurate depth of the square was also measured, 6.8 m to the yellow surface on the day but this will vary with flow and water level effects.
I have setup the survey box so that it logs data continuously, this allows the diver to retreat whilst measurements are taken minimising any magnetic effects of steel cylinders or other dive gear, this is apparent in the good agreement between foresights and backsights taken, they are no worse than what I have measured on land away from ferrous materials. The upper part of the dig is festooned with scaffold and other metal things.
The survey data was input to Survex and corrected for local magnetic deviation, a resulting bearing of 161° to was calculated for the lipped edge of the plastic square.
The model was processed without issue and was manually scaled, rotated aligned and translated with the survey data measured and the entrance location provided by the cave registry in CloudCompare.
The video from one of the dives can be seen here, attempting to slowly film the waters surface from underneath, down the rift to the current dig face.
A flythrough of the model is available to view below:
More Porth….
Over the summer months this year (2021) I continued to visit, survey and video various parts of the cave upstream of Upper Cave Water Chamber. The results are very pleasing because not only is the level of detail being captured far in excess of any survey that has been conducted before (at this site) but this detailed data (the models produced by photogrammetry) is also matching well with the Distox2 data which gives real world scale and orientation meaning its not just pretty pictures which I prefer to avoid.
This area of the cave lends itself very well to my process as each section is short and clearly divided by short sumps giving nice workable areas to focus on. The below image shows a comparison with the UBSS survey in plan view.
Where to go next ? I would like to improve the alignment of Sump 9 relative to the rest of the model as so far this has just been best fitted to the other data and I would prefer to link it directly. After this then adding the passages in Parker Series is the next logical step but perhaps this will have to wait until next summer.
I have uploaded the models of the three dry sections to Sketchfab, its low resolution due to the limits on the free account.
Porth yr Ogof Sump 9
Porth yr Ogof is a cave situated in the Brecon Beacons in South Wales frequented by divers as well as dry cavers, I believe it has the largest cave entrance in Wales.
The naming convention is rather confusing in that to reach sump 9 you start in sump 3 at the Tradesman’s entrance, dive through sumps: 3,2 and 1, before exiting the water for a short section of passage (Upper Cave Water Chamber), before diving sump 8, crawling for a short while before diving sump 9, the subject of the post. It is also possible to start in sump 1 entering via the Top Entrance negating about 150 m worth of diving by missing sumps 2 and 3, information and an old survey can be found here:
Click to access UBSS_Proc_15_3_259-0.pdf
Late in 2020 I visited Parker Series which is the dry section of the cave guarded by sump 9, after diving through it struck me how ideal a place it was to attempt to create a model using photogrammetry. The water is usually clear and the passage is mostly formed as a small tube meaning cheap lights and cameras would make a reasonable job of it.
I set off on a second trip with my Gopro Hero 3+ and Ebay video lights and moving very slowly captured stills every 0.5 seconds using the interval function. It took around 300 images to cover the sump each way. The Ebay video lights I used do have an odd colouration where they overlap but this doesn’t bother me, it might bother photography purists but my main intention is to measures the size, shape and direction of the passage and for this true colour representation doesn’t matter.
Loading the 300 images into the software and processing the images yielded a nice accurately aligned point cloud of the sump, I didn’t cover the three side passages on this occasion so these are missing but the smooth curves that the passage follows can be clearly seen, the UBSS survey lacks detail in comparison.
Whilst a nice representation of the sump has been created it bears no orientation or dimensional reference to the actual passage. I visited again with the intention of covering the side passages and adding a means of aligning the data to magnetic north, absolute depth and scaling it so that distance and size was more accurately represented.
To do this I took a plastic builders square (with weight attached) and my survey device back to the sump, I dived a short way into the sump before placing it on the floor and returning to the start for my camera. I then took photos through the passage as normal this time covering the builders square on the floor. I continued to the first side passage and tried to cover as much as possible of it. Once this had been done I placed my survey box on the raised edge of the square to be used as a heading reference and took 2 for-sights and 2 back-sights. I had programmed a timer so that I had time to retreat a few metres for each shot so as to minimise any magnetic distortion from my diving equipment being close to the magnetometer. The fore and back sights agree quite well so it was worth doing this.
I repeated the process towards the end of the sump so that I had two heading references (one to align to and one to check against), the depths of the centers of the yellow square were measured to align the depths to and the edge of the yellow square was used to estimate scale from. Once out of the cave the photos were then processed to generate a new point cloud containing the yellow squares which were then rotated, translated and scaled to the ‘correct’ figures.
Survey and model video to follow….
DIY Helmet Mounted Caving/ Diving Light
There are multiple options for cavers who like diving through sumps to further their caving trips to choose from in the lighting department, the likes of Scurion, Phaeton, Rude Nora and other manufacturers have been making suitable lights for years.
This being the making category of this website you can probably see where this is going !
Sometime in 2018 I discovered the LED driver board (the heart of any modern lamp) for the Phaeton was available for purchase from its designer/ manufacturer in the States which is:
I duly ordered a couple of boards, some CREE leds cobs and a suitable switch (tricky to track down and a few month wait for stock). Once these had arrived I soldered the bits together then proceeded to procrastinate for a while whilst trying to figure out how to solder and assemble the 20 pence piece sized board inside a small water proof housing.
This went on to the point where I became more interested in other things and forgot about the parts I had, occasionally coming back to the problem but finding no solution.
My whole cave/ sump diving career has involved the use of a hotch-potch of different hand held lights attached to my helmet, great for redundancy but heavy out the water. For caving trips only I would remove these lights and attach a Petzl MYO which is nice and light in comparison.
I’m not one for caving with super bright lights, its nice to have the option to occasionally use full beam to light up distant parts of passages but for the most part i’m happy to cave on dim settings. During the late summer of 2020 the diggers of Wookey 20 (website in links) had broken through into what they have named ‘The Land of Hope and Glory’ in which was an enticing aven was found and to be climbed by myself and the bolt climbing veteran Tom Chapman.
We duly arrived with equipment and the other proceeded to use their highly powered caving lights to light up the roof of the aven some 30 m above. I set my Petzl Myo to full and could barely see anything !
This lack of power is what reignited my want for a powerful light that was waterproof enough for any diving I had planned and brighter than what I had already. Its main use would be for caving the other side of sumps, centrally head mounted lights give lots of backscatter so are of limited use as a primary light underwater in normal British cave diving conditions.
The parts I had obtained in 2018 were dusted off and I had a fresh look at the problem, mainly the soldering and assembly in such a confined space to keep the overall size and weight of the light down. No futher progress was possible with the idea in my head or in CAD modelling. so I decided to just start making a housing and and to try and assemble it and make it up as I went along.
Strangely, once I had roughed out the housing the ideas started flowing and after a few eureka moments I found a way to assemble it so construction started in earnest.
The body is made of Acetal, with a 5mm Polycarbonate front and an Aluminium heat sink for a rear both sealed by o rings. The battery box houses two 18650 batteries and is made of Acetal.
After having assembled a working version in Autumn 2020 I took it for a few trips, although the light remained dry it worked very nicely in Raven’s well, it didn’t overheat which was one of my concerns using a plastic body and metal backing plate and the combined spot and flood lenses gave a nice pool of light to cave with. A more testing trip a week later in Swildon’s Hole involving free diving to sump 6 however proved it to be less than waterproof. The light worked really well on the trip and owing to the conformal coating I had put on the exposed electrical connections it continued to work even when wet inside but on inspection on the surface it had a fair amount of water inside given the shallow and short nature of the sumps.
The possible source of the leak perplexed me for a while, I kept taking it apart checking things then taking it for a dive only to have it consistently leaking. Whilst descending from the surface with it in my hand so that `I could visually see where the water was coming from showed that it was leaking by the switch which has an o ring seal on.
Taking it apart and drying it again and inspecting the switch showed that the threads didn’t go all the way to the sealing surface on the switch lip, meaning that when it was screwed down onto the body it couldn’t go down enough to actually engage the o ring and the source of my troubles. These switches are meant to be mounted in a panel using a clearnce hole for the threads and a nut the other side instead of being installed into a threaded body like I had done. What I needed to do was cut a small relief diameter to the top of the threads on the light body so that the switch could be screwed all the way down to compress the O ring and make a seal. I tried this on the light I had made already (v2) but messed it up so version 3 was ‘born’ with a funkier cut away shape and the extra clearance for the threads.
Pressure testing the light on dives and fixing it in between had become a rather exhausting process so I decided to fashion a small pressure pot out of some clear pipe, some end caps I had used on a small dry tube previously, an old bike inner tube valve and a bike pump. Using this setup I was able to cautiously test it to 80 m depth in my back garden.
I am happy to report some months later that after a few diving trips it has been working very well, I have since changed the LED’s to those with a warmer colour temperature, I find this easier on the eyes. Caving with the light on the second dimmest setting gives ample light and even with the occasional bursts to full I am getting many hours before I am having to recharge it.
I have it mounted to my original Petzl Spelios helmet (with the Duo removed) and found that due to the foam in the helmet when inadvertently left in a sump pool the whole lot floats which is a nice benefit, no more worries about dropping and loosing a helmet into the murk.
Small Waterproof Boxes
Keeping small delicate items dry whilst transporting them through sumps can be done using a variety of containers.
Common small items that might be useful are: Spare batteries for lighting, disto’s, small cameras, or maybe some cigarettes and a lighter !
Inside ones drysuit might be the easiest option (if worn) though lithium batteries inside a suit under pressure might not be best idea and the item(s) may become uncomfortable during the dive due to migration and suit squeeze.
I have a few small containers I have successfully used to carry items through shallow sumps, pictured above are two boxes from Inglesport, an old UK400 torch body and a small home made drytube.
The smaller Inglesport box has enough room for a DistoX2 (if foam is removed) or an Olympus TG4 (waterproof itself to 20m) but not much else. This has survived many a dive to 25 m without leaking.
The larger Inglesport box I have has more room inside than the yellow one, I can fit the disto, an old android phone used for surveying, tipex and a few other small items quite easily inside, this has also done a few dives to 25 m without issue.
For deeper dives I prefer to use my old UK400 torch body, i’m not sure of the exact maximum depth rating of these torches but this one in particular has been to 50 m without issues many times in its previous life as a torch and would likely go deeper, there is the larger version the UK 800 if more space is needed. Its downside is the odd shape though the handle could be cut off to make it smaller if required.
The other item in the photo at the top is a small dry tube I made, it is untested below 25 m and has a larger capacity than the boxes or torch, I used it Mexico to take some dry clothes (merino wool leggings and trouser just about fit in it) through a sump to sleep in whilst camping. Both lids seal with barrel o rings and a large snoopy loop holds the lids in place, once underwater the pressure holds the lids in place.
Small containers like these do have a small amount of bouyancy but this can be offset with rocks or just ignored.
Memories of Dive Base
A collection of photos from various caves where the diving begins.
