Open source underground
Mike Bedford on why caving needn’t only pose a physical challenge – it’s also your chance to try out exciting bits of Foss-powered kit!
Mike Bedford discovers why caving needn’t only pose a physical challenge – it’s also your chance to try out exciting bits of Foss-powered kit!
Those of you who want to exercise your mind and body at the same time might balk at our suggestion that you take up caving. Yet, as we discovered in LXF244, when we looked at the technology of cave surveying, venturing underground can pose both a physical and a mental challenge.
However, the technology used in caving doesn’t have to end with hand-held electronic surveying tools and laser scanners, coupled with open source Linux software for post-processing and map preparation. Here, we’ll look at how technology can be used in exploring caves, photographing them, monitoring the underground environment for scientific research, and even minimising the risk involved in venturing into these potentially hazardous (my dad tells me it’s
perfectly safe–ed) environments.
You might be surprised to learn that our main theme isn’t the use of Linux software, although that does get a look in. Instead, we’ll mostly be thinking about technology that cavers can use while they’re underground. Laptops – even specially rugged ones – don’t survive long if they’re being dragged through muddy caves. For this reason, we’ll be looking at applications that run either on single board computers, or on microprocessors or microcontrollers that form part of dedicated hardware. Some of these applications are Linux-based, running on Raspberry Pi or similar hardware, while others are embedded applications that don’t run under any operating system. Despite that, though, Linux offers everything that’s needed for developing the embedded code. Oh, and a smattering of Android apps, since smartphones are more forgiving of knocks than laptops.
We hope some of you will take up the challenge of developing caving tech and, if this appeals to you, we’ll show you how to safely take your first steps underground.
CAVERS ADOPT SELFIE CULTURE “Cave radios have mostly been designed for speech communication, but there are various options for using them to exchange texts or even photos.”
If you were to venture underground, you’d probably find that your mobile phone signal would be lost within just a few metres from the entrance. Most other radio signals would suffer a similar fate. On an ordinary caving trip, being without a signal for a few hours isn’t a problem, and it could even make a welcome change, but there are times when contact with the outside world can make all the difference.
On long caving trips lasting several days, communication could enable the surface party to give warnings of changing weather conditions such as the onset of heavy rain that could cause flooding underground. And this isn’t the only circumstance in which remaining in touch could be a matter of life and death. Cave rescue teams can also benefit from reliable communication. For example, since exiting a cave with a badly insured casualty could take hours, being able to summon medical assistance to be on-hand when the team reach the cave entrance could be critical.
While mobile phones and most other commonly available type of radio equipment rely on signals that are absorbed by rock to varying degrees, if the frequency is low enough then radio signals can penetrate the ground sufficiently to provide communication between a cave and the surface. Lowfrequency radios, which would be suitable for use by cavers, aren’t generally available though, and so equipment is mostly designed and built by cavers. At one time, these so-called cave radios were built using analogue electronic techniques, but recent designs have tended to use digital methods, at least in part.
The Micro Heyphone, built by caver and electronic engineer Ian Cooper, is a hybrid design. While it uses some analogue circuitry, Ian made it considerably smaller, and hence more portable than previous designs, by adding an Atmega 328 microcontroller from Microchip Technology. The microcontroller is responsible for all the control functions and for generating the radio signals, while analogue electronics carries out the modulation and demodulation functions.
The hybrid approach of the Micro Heyphone allowed for a more rapid development programme, since some of the analogue circuitry from earlier designs could be reused, but DSP expert Ron Taylor’s Subphone is a more revolutionary design. This new cave radio, which has been used on caving expeditions in Spain, is a purely software design that runs on a Dsp-based (digital signal processor) single board computer. The board is called the Eden DSP and it uses a PIC DSP chip for which a Linux development environment is freely available. Full details of the board are at https://groups. io/g/edendsp, from where you can download files that you can use to get a PCB manufactured.
While most cave radios have operated in that portion of the radio spectrum officially designated as LF (low frequency), which covers 30-300khz, some people are now experimenting with operation at VLF (very low frequency), which covers 3-30khz. Should this prove successful, it’s anticipated that it’ll make possible communication in environments with more conductive rock where conventional cave radios struggle.
Rather than building dedicated hardware just to experiment with techniques, though, initial investigations, at a frequency of 9khz, has involved using software on laptops, employing their sound cards for generating and receiving the signal. The software of choice has been the open source GNU Radio Companion,
(see Lxf261/2)which enables a software-defined radio to be designed by wiring up functional blocks on-screen. The design is being ported to a Raspberry Pi to provide a more portable, less-fragile solution, possibly as a halfway stage towards a fully embedded design.
Cave radios have mostly been designed for speech communication, but there are various options for using them to exchange text messages or even photos. Photo transmission is an interesting problem. Because of the requirement to use a low frequency, the bandwidth of cave radios is very small, so image exchange is never going to be quick. However, by connecting an Android phone to the cave radio, and using an Android app to support SSTV (slow scan television) – which is mostly used by radio amateurs to transmit pictures via shortwave radio – photos have been sent from a cave to the surface in a few seconds. We can envisage that this could be useful during rescue operations.
Exploration down under
Surveying and communication are probably the areas that have most exercised the minds of technicallyminded cavers, but exploration is the essence of caving, and here too technology is now playing a part. Of course, crawling down tortuous narrow passages in the hope of finding the fabled “caverns measureless to man” has always been a part of underground exploration, and for some it’s a challenge they actually relish. But in the largest of unexplored caves, with so many possible avenues for exploration, using robotic vehicles can improve your chances of success.
Aerial unmanned vehicles, commonly known as drones, are probably the most commonly used type of robot in cave exploration. Even though they’re widely available they don’t offer the same opportunities for experimentation. Yet a couple of examples show how useful they can be.
Swiss Drone manufacturer Flyability, for example, used its Elios 2 vehicle – which is housed in a spherical mesh shell to allow it to survive collisions – to explore the Aven d’orgnac cave in France. This is partially a tourist cave, although much remains to be explored because of its protected status. Only limited access is provided to caving clubs, but permission was given to investigate the cave’s various chimneys, or avens as they’re called by British cavers, using Elios 2. This eliminated wasted time in climbing the avens, some of the 70m above the floor of the chamber, only to find that they don’t lead to unexplored passages. After exploring 11 of these chimneys in two days, the comment was made that this is probably the ‘softest’ tool they have available for cave exploration without harming the natural state of the cave.
While the drones themselves might be available off the shelf, though, there’s still considerable potential for working with drone footage. Caver Juan Corrin has been using a drone as part of an ongoing British expedition to the Matienzo region of northern Spain. In this case, the drone isn’t flown underground, but on the surface with a view to spotting new cave entrances. Juan’s work has involved combining drone flight paths and footage with surface maps, satellite imagery, cave surveys, hydrological information and so much more. This is done in a free open source GIS (Geographical Information System) called QGIS. The Qgis-based Matienzo GIS is available from the expedition website at www.matienzocaves.org.uk. It’s interesting to note that a cave called Torca del Dron – which has now been explored 167m vertically from its entrance and still has more to be investigated – was discovered using a drone’s panoramic photos.
TAKING THE DRONE OPTION “Aerial unmanned vehicles, commonly known as drones, are probably the most commonly used type of robot in cave exploration.”
There’s gold in them thar caves!
“In the middle of the 1800s, settlers were flocking to California in search of gold that had recently been discovered there. In an effort to discourage settlement, native Americans often tried to make efforts less profitable by robbing mining operations.
“There’s a legend that in one such incident, two prospectors were robbed and killed, and the bandits made away with an estimated 100 pounds of gold. A sheriff’s posse was gathered to chase after the men and a chase ensued through the hills. The gold the men stole was so heavy that, in an effort to get away, they had to ditch it. Eventually, the sheriff’s posse caught the men and demanded that they confess the location of the stolen gold in exchange for their lives. The men said they hid it in a cave now known as the Hall City Cave near Hayfork, California. Despite the posse’s promise, both men were hung on the spot.
“When the posse went to the cave, they reportedly found a two-metre diameter hole, filled with water, going straight down as far as they could see. Presuming the gold was thrown down this bottomless pit, and with no technology to dive down the hole available at the time, they gave up.”
This narrative, by Eric Stacpkpole, sheds some light on his motivation for developing OPENROV. Unlike flying robots, unmanned vehicles for underwater exploration are not nearly as widely available so Eric designed his own, based on the Beaglebone Black Linux-based single board computer, published the design, and made kits of parts available for purchase for less that $900.
So far as we know, Eric never did find the gold, but OPENROV (https://forum.openrov.com) has since been
used in the exploration of several caves, including during a National Geographic sponsored expedition to flooded caves in Mexico’s Yucatan Peninsula.
Underground photography
Cave photography is capable of creating some stunning images, but as we move on to look at this artistic underground endeavour, we don’t always find the latest in technology. Indeed, the opposite can be true. For example, they might sound positively ancient, but many cavers prefer to use old-fashioned flash bulbs instead of electronic flashguns, and you can still buy them, albeit mostly as old surplus stock. Apparently they can be much brighter than today’s flashbulbs and have a wider angle of illumination – both characteristics that are handy in large chambers – and they have a longer burn time, thereby giving a sense of motion to flowing water. However, a recent development by Rob Gill, editor of cave technology magazine CREG Journal, combines caving, photography and Raspberry Pis.
It transpires that cave formations – for example stalactites, stalagmites and flowstone – often fluoresce. In other words, if you shine an ultraviolet light on them they emit coloured light, commonly a pale blue, changing their appearance from their usual white colour. Obviously, there are artistic opportunities here but it goes further. Fluorescent calcite formations can also phosphoresce, which means that they continue to glow, usually in a different colour, for a second or so after the UV light has been turned off. However, capturing that afterglow can be tricky, because the brightest phosphorescence is immediately after the UV light has been turned off so it would require good reactions to get a good shot. To solve this problem, Rob’s Rpi-based contrivance turns on a bright UV light source to “charge up” the cave formation, then turns it off before immediately triggering a camera.
Over to you
Part of our motivation in bringing you this article is to inspire you to get involved in an unusual aspect of technology. If you do decide to further develop the stateof-the-art in cave technology, though, there’s something