SMCC THAILAND SURVEYING METHODS
This paper seeks to record and describe the way that cave surveys are conducted on the Shepton Mallet Caving Club trips to Thailand. The aims of what we are trying to achieve are set out, the methods and techniques used are detailed and there are notes on instrument calibrations and how the data is compiled and archived.
It is hoped that by recording this information the Thailand project can continue to expand and the survey data can be managed in a logical manner. As of July 2004 there were 284 file names associated with Thailand book and survey files in the Walls survey project. These surveys added up to 25,761 m of centre-line (excluding surface surveys) in 55 caves located in 11 provinces.
In Thailand we are doing exploratory work and it is vital to get a good survey of all the caves and to know where they are geographically. The cave surveys should be done fairly accurately, but due to time constraints there is no need to waste time taking too many notes or surveying too precisely. However, as many of the caves may only be visited briefly we will probably not have the opportunity to return if any mistakes are made or anything forgotten. Thus it is important to ensure that all the necessary measurements have been taken and that the notes are clear and make sense. It is quite possible that the survey will be drawn up by someone who has not visited the cave. Thus the survey notes need to be as detailed and as complete as possible.
When surveying into a new cave we are also exploring it. We need to push the boundaries of the cave so survey the passages that lead into unexplored regions rather than getting involved with surveying a small network of rift passages near the entrance. The best route to take is usually the path of least resistance and this also makes the surveying quicker and more pleasant. By placing a marked survey station at the start of all the side passages they can be returned to later if there is time.
Be very careful about starting the survey at the end of the cave or passage. If you do start at the end you are committed to completing the survey back to the entrance or a known point in the cave. If you don't connect with the surface or a known point the survey will be 'hanging', i.e. it can't be fixed geographically, and is nearly useless. It is always advisable to survey into the cave as the survey can then be stopped if necessary (e.g. due to running out of time, losing the survey instruments, a survey team mutiny or other problems). I can understand why it is tempting to survey out of the cave having rushed through it to explore it first, but please be cautious about doing this.
There is not a "if you find it you must survey it" rule, but there is moral pressure on the discoverers to make sure that a survey is done even if by others. Each team should have a surveying kit with them when wandering about in the jungle. This can save them from having to fight their way back to the cave on another day by surveying the cave when it is found. As a guideline I would say that any cave over 100m long must be surveyed to at least a map-reading compass and calibrated pace standard. All entrances, sinks and resurgences must be GPS logged or have their position pin-pointed on a map.
It is easiest if the survey progresses down the centre of the passage, though this may not be possible in a river cave where the surveyors are clinging to the walls. Progressing down the centre of the passage and stopping in the middle of junctions makes it easier to relocate stations in the future. The biggest source of errors, after misreading or misrecording the instruments, is station position error so it is important for the stations not to move. The tape man must not wander off just because he is getting bored, but has to stay on station until released by the instrument reader. Leapfrogging is the best technique as this helps to cancel out systematic errors in the instruments, but don't bother in passages where you can't overtake. Use the instrument reader and tape man as the stations for most legs.
Set a station when the end of the tape is reached, the end of the line of sight is reached or at a junction. When picking the station remember to check that you have a sensible view further up the passage as well as being able to see the previous station. Mark various stations as the survey progresses. Tippex or nail varnish are good, just put a spot and station number on the wall, floor, boulder, etc. near where you are stood. At the end of a survey trip mark the last station with orange flagging tape. Also mark stations at junctions with flagging tape. For these marked stations you can have a "down" station where the readings are taken to the marked point (which could also be on the wall or ceiling) instead of to the tape man. Make a note of which stations have been permanently marked in the survey book. Also mark the station at the cave entrance, preferably with tippex or nail varnish. The entrance station should be close to the middle and at the overhang. If the bolting kit is with the surveying party a permanent survey station can be marked by drilling a shallow hole. These permanent survey stations should be at the entrance, at the end of a survey and/or at major junctions. Only a few are needed and they should be clearly marked in the notebook along with a description as to where they are. It would have been very useful if a lot more stations had been marked in some way in complicated caves such as Tham Takobi and Tham Loe Pu. This helps the various surveys to be joined together in a lot more accurate way than trying to guess the position of the station that joins the surveys.
Closed loops (i.e. surveying round in a circle back to your starting point) are good for showing how accurate your survey is. Closed loops are also good for showing how inaccurate your survey is. If you get within a 1% error on a closed loop you have done very well. Fortunately the computer is very good at sorting out the bad loops.
The best size for a survey team is three people: tape man, instruments reader and note taker. A fourth person can be useful for going ahead of the survey team and finding the route for them as there is nothing more embarrassing then accidentally surveying back to where you started from having missed the way on. Surveying can be done by only two people, but this is slower.
In a noisy cave (lots of water or bats) the tape reel should be with the instrument reader and the book man should stand nearby to be able to hear the readings. It may also be advisable to limit leg lengths to only 10m in a noisy cave to help communication between the team. In a quiet cave the tape man can have the reel and take the distance reading as this will speed up the survey.
The tape man is usually the "gofer" of the team and is likely to be sent up all the side passages, wading into deep water pools first, made to fight through the cobwebs and flood debris, etc. Normally he gets to hold the tape reel and read out the distance before winding the tape in and letting it out again as the instrument reader overtakes him. However, in a noisy cave he may end up with the dumb end of the tape and have little to do except act as a lighthouse for the instrument reader to aim at. This is usually the apprentice's job.
· Check that the tape starts at zero. If not note the missing length in the notebook, but don't apply a correction underground as it can be done by the computer and the computer's maths is better and more consistent than yours.
· Make sure the tape isn't snagged and pull it taught. On a long leg this will take some effort, but try not to pull the instrument reader off their feet as he will only get upset.
· Keep the maximum leg length to 30m (i.e. the tape length) to help reduce errors.
· Do not use the tape as a hauling or hand line as it will stretch. Be careful when plumbing depths not to get it snagged.
· Read the correct side of the tape. Use metres please.
.
The instrument reader should have fairly good eyesight and know how to operate the tools. Even experienced readers should check the compass and clino in use on the day as they are all different. The compass and clino are designed to be read with the right eye and with both eyes open.
It helps speed up the note taking if the readings are read out in the same order every time. The readings should be in the order of tape, compass then clino. This is also the order in which the data is entering into the computer and will thus speed up data entry. To help reduce confusion compass bearings should always be read out as three digits, e.g. zero one zero instead of ten, and the clino should always have a plus or minus in front of the reading even if it is obvious you are going up a 45° slope. Take readings to the tape man's light, either on his head or when he puts it on a down station. Read the instruments two or three times to check the measurement, there is no rush as the note taker will always be slower than you. Try to keep the instruments as dry as possible. They are waterproof, but once wet condensation can form inside the instrument making them impossible to read. Problems have also occurred when the instruments have been taken out from an air-conditioned car. There are several ways of trying to remove the condensation: licking the eye-piece, dunking the instruments in cold water (but be careful not to get them muddy or gritty) or holding them upright and tapping them sharply (don’t do this too vigorously or you will damage the instrument). It is important to dry out the instruments after a trip. Sleeping with the compass and clino has been found to be particularly effective at removing condensation!
· Hold it level. Not doing this is a big source of errors. This can be difficult on a steep downwards slope, but using the tape can help the sighting. The use of vertical legs can sometimes help to 'bypass' the steeply inclined legs.
· Very important – keep your light away from the compass as many lights are highly magnetic. Experiment and check at what distance your light affects the compass. Also be careful of metallic objects such as watches and spectacle frames as they can also cause magnetic interference. A small handheld light such as a Tikka or Q40 is very useful to illuminate the instruments.
· Beware that the scale reads from right to left – 150...140...130 – so take extra care when only one number is visible.
· Some compasses have a small number underneath the big number. This is the back bearing – ignore this number and use the large number
· Make sure you read the correct scale. Most clinos have two scales – they all have degrees and most will also have percentage. Make sure you read the degrees scale. Check this as at low angles the percentage is similar to the degrees. However, if the percentage scale has been read continue reading percentage and make a note in the survey book. The computer can use percentage instead of degrees.
· Check that the clino is not sticking and moves freely.
· Make sure you hold it the right way up with the window on the left. Your light can be held against the clino to make reading it easier as it isn’t affected by magnetic fields.
· Take care on shallow slopes as to whether it is + or – as this can be tricky (if the sighting line is above the zero it is a negative value). Tilt the clino markedly up or down to check.
This is the most important job as the note taker checks that all the necessary readings have been taken and makes a sketch of the cave. The job is usually done by the most senior surveyor or the most artistic. The note taker will always be the slowest member of the team, but it is important to make sure he gets it right.
· Use the survey notebooks provided. Use one of the waterproof books in a wet cave (they can also be useful in hot caves where you may sweat profusely) Don't feel you have to fill up every line on a page before starting a new page if it will help keep the notes clear. Mark each page with the date, cave name and page number for the survey session. Also record who was in the survey team (tape, instruments and note taker) and which set of instruments were used.
· If returning to a cave the station numbers do not have to continue from where you stopped. You can start from 1 again and let the computer sort out the rest. If you like you can also use letters e.g. use A1, A2, A3… or 12a, 12b, 12c… for surveying up a side passage to help reduce confusion.
· The left and right wall distances are taken facing the direction the survey is progressing, not the direction the instruments were read otherwise they flip over every station when leapfrogging which is a pain when drawing up the survey.
· If using the laser or tape to measure LRU readings only record to the nearest 1m as I can't draw more precisely than that. Otherwise just estimate to the nearest 1m.
· It is a bit of an art deciding where to measure the LRU to: what do you do if you are in a trench or under an overhang? It is usual to take the readings at eye level as this is what the caver will see. Steeply inclined bedding planes are particularly hard to estimate.
· Mentally check that the readings are correct and not rubbish, e.g. if you have gone round a 90° bend the bearing should change 90° (this is tricky when leapfrogging!).
· Always read back to the rest of the team what you have written in the book, not what you think you heard. Do not rub out mistakes, cross them out and write the correction near it. Do not use decimal points use a slash mark. Use pencil as this is waterproof. Be careful of mud as this can very effectively scour the pencil off the paper.
· Try and keep the sketches neat and fairly accurate (if the cave bends left show it bending left). Show the station numbers clearly and accurately on the sketch as these sketches may be used in the future to relocate the station. Also show side passages, etc. If done perfectly the sketches will look like the final survey with passage widths and bends all in the correct proportion. This rarely happens in practice.
· Record as much floor detail as possible (sand, mud, stal, guano, cobbles, pools, stream, etc.) as well as columns, 'mites & 'tites, flowstone, gours, faults, joints, etc. It is clearer if these are added as text around the sketch with arrows showing their location rather than trying to draw the symbols on the sketch.
· Take cross section sketches. It is recommended to draw a cross section every 5 stations or where the passage noticeably changes shape.
· Always carry spare pencils (they do float though), notebooks and some tippex pens, nail varnish or tape for marking stations.
· When the day's surveying is finished guard the survey notes. Make sure the other members of the team know where the notes are so that in case of emergency they can leave the cave before you are rescued.
· On returning to base camp enter the data into the computer, preferably before going out for the evening. This allows you to decipher your notes and maybe remember unrecorded data whilst the mind is still fresh and before it has been addled with Sang Som.
For a Grade 5 survey the compass and clinometer have to be calibrated. However, due to either the lack of availability or poor quality of the topographic maps it is not possible to obtain a magnetic declination locally. To correct from magnetic to grid north the built in correction in Walls is used. This uses a mathematical model based on date and location. Thus it will not account for any local magnetic anomalies or magnetic storms.
It is possible to correct for differences between the various instruments. The definitive set of instruments, to which the others are calibrated, is the SMCC Silva Sightmaster combined compass and clinometer (#225377). The corrections to calibrate the other instruments to this master set are
Compass corrections:
Sims Suunto #024138 zero
Ellis Suunto #723445 inca=1
Clinometer corrections:
SMCC Suunto #539569 incv=-1
Ellis Suunto #726759 zero
The first explorers of a cave usually have the right to name the cave and passages. However, in Thailand it is more than likely that the caves have already been explored by the locals. The cave name should be the local name (if we can find out what it is!) or the name of a nearby river, mountain, village or noticeable feature. If possibly get the Thai name written down in Thai (from signposts, painted in the entrance, asking locals or guides) as the Thai names are more consistently than the numerous variations possible with English transliterations. Please write these down by printing as clearly as possible, or take a photo of the sign. We should try to avoid names like Tham Lot (Large Cave) or Tham Nam (Water Cave) as there are hundreds of these in Thailand. It is probably best to use code letters and numbers until a Thai name can be found.
There is not much point inventing a huge list of names for various parts of a cave that may never see another Westerner. In longer cave systems names may be required to help differentiate between the various parts of the system. These names should be descriptive and kept to an absolute minimum. I personally don't approve of joke names or naming them after individuals.
It is better to survey between caves that are close together, say less than 300m, as this will be more accurate than relying on GPS fixes. It can be done with the underground compass, clino and tape, but undergrowth can make using the tape difficult. Surveying a short part of the area outside the caves, such as the stream and paths and locating nearby buildings, etc., improves the look of the finished surveys. You will still need to sketch any surface surveys.
Finding the altitude of the caves has always been a problem in Thailand. If 1:50,000 maps are available the best method is plot the GPS fix and to use the contours (which are at 20 m interval). However, the contours and spot heights (for hill summits and the bottom of dolines) are not as accurate as they could be. If the large scale maps are not available the GPS altitude will have to be used even though these can be out be tens of metres. In addition different map datums will give different altitudes e.g, there is a difference of around 50 m between the altitude datum used on Thai maps and the WGS84 datum. Altimeters have not been used as we don’t have any points of known altitude to calibrate them.
The use of GPS in the field is an art form. Fortunately we have a couple of well practiced GPS users in the club and have had a lot of experience of using GPS on caving expeditions. The first thing to note is that GPS receivers, specially the hand held ones, are not as accurate as the manufacturers claim. It is also important that the GPS is set up correctly and used in the correct manner. These notes will give some guidelines on GPS use. Fuller coverage on expedition GPS use is given in the paper published in the SMCC journal.
The GPS receiver must be set to the correct datum or the co-ordinates obtained will not match the maps. Set the datum to Indian 1954 (Thailand-Vietnam) [given as Indian-Thailand on Garmin machines] not the GPS default which is the WGS84 datum. The map datum is actually Indian which isn't supported by Garmin GPS so we have to compromise and use this Indian-Thailand datum. The Indian datum moves a point 60m west from where it was on the Indian-Thailand datum. The grid should be set to UTM.
Don't believe the EPE. This stands for Estimated Positional Error i.e. the machine is guesstimating what the error is. Use it as a guide and don't take it as gospel.
GPS receivers struggle to ‘see’ the satellites when under tree cover or close to a cliff. If you can't acquire at the cave entrance go to a clearing to acquire then walk to the cave as this may allow the GPS to track the satellites through the trees. When taking a fix don't take the first reading after acquiring, wait at least 5 minutes for it to settle down. Alternatively take a fix in the clearing and survey in to the cave. Please make sure this is clear in your notes as there have been cases in the past where people have "fixed" an entrance, but were actually many metres away in order to get coverage. It is important to accurately tie-in the GPS fix position into the cave survey so the GPS station should be marked. Some GPS units have an averaging function. This allows the unit to be left on for many minutes at a location and allows for a much better fix to be obtained, particularly of altitude. Although this is a potentially very useful tool it has not been used yet in Thailand.
If your machine doesn't do it when saving a waypoint record the GPS altitude in a notebook. GPS altitudes are not very good, but are better than nothing. They improve after the GPS has acquired a full set of satellites.
In the notebook record a description of what the waypoint is, what the EPE was and it is advisable to also write down the grid ref in case of a waypoint deletion disaster. The EPE should be recorded as this value can be entered in Walls and the program can take this estimated error into account when compiling the survey data. I end up with lots of sets of waypoints 1, 2, 3, 4, etc. so please use more descriptive names.
When recording tracks (e.g. the path to a cave) set the recording to automatic. Allow the GPS to acquire and settle down before switching on the tracking. Switch off the tracking if you go back along a part of the route and if you have switched off the GPS allow a few minutes for it to settle down before taking the new path. With Garmin GPS units if the track is saved the GPS compresses the data and many points on the track are lost. For a good quality track it is important not to move the track to one of these saved tracks, but to leave it as the active track. If there are a couple of GPS units with the group they can be used to track different routes.
It is important that all information is recorded somewhere. With a large group exploring an area over several years there is a danger that information will be lost as GPS fixes are deleted, jungle bashing exploits not recorded, water samples forgotten about, etc.
To help overcome this everyone should have their own notebook and they should use it to record any cave and karst information they may find. If this data is recorded by everyone on that trip there is less chance that the data will be lost. In addition different people see different things on a caving trip so this will help record the cave more fully. There should also be an expedition log book to record the day's exploits in. In the log book there should be recorded who was there, where they went and what they saw. Amongst the information which should be in the log book are the GPS waypoints, geology of the area, wildlife seen, where any water samples or air measurements were taken, a quick description of any caves found and anything else that may be of later use. The results of any water tests and the progress of the surveys will also be recorded in the log book.
A computer database, Speleobase, is being used to record the cave data in an electronic format. This program does have its limitations, but has text fields for recording location details, exploration history, the amount of work done in a cave, etc. as well as numerical data such as cave length and grid co-ordinates.
Along with the entrance location data the most important data which we will be collecting is the cave survey notes. We still haven’t come up with a totally satisfactory method of archiving the cave survey data. Various cave survey notebooks have been used including custom printed paper booklets, professional surveying fieldbooks and waterproof notebooks. The main problem is filing the data so it can be readily accessed and having the field notes available on future surveying trips. The original notes are too valuable to go back to Thailand and certainly not to go into the cave again. It is hoped to photocopy all the survey notes and then file these by cave. The original survey books can then be deposited in the SMCC library.
The cave surveying software used is Walls. All the Thailand survey data is in a project called “Thailand”. The data is then divided into books by province. These books may be further divided into regional books. Short caves which have only had one survey trip may have just the survey file, while longer caves are stored as a book with each survey trip as a separate file.
Thailand
Chaiyaphum
Khon Kaen
Phetchabun
Nam Nao National Park
Tham Yai Nam Nao
Surface Surveys
20040106 - Tham Yai Nam Nao entrance to GPS
20031228 - Tourist Cave
20031229 - Ladder to CO2 sump
Tham Yai Nam Nao Resurgence
Tham Song Hong
Tham Pha Rai
20040102 - Entrance to Downstream Boulder Choke
The survey files should have a date and description of the part of the cave surveyed. A masterlist of the Walls file names (the 8 character name used to identify the different files) is kept as an Excel file. Use the file name as the prefix (remember that these are case sensitive) as this is a considerable help in tracking down any duplicated station names. The use of a logical naming convention helps to avoid these file name sharing conflicts.
Various flags and segments are used and these should be consistent for the whole project. The segments used are
/cave thin solid khaki line khaki
/cave/unsurveyed thin dashed khaki line
/cave/stream thin solid blue line blue
/surface thin dashed purple line purple
The following segments are used for surface features and GPS downloads
/contour for surface contour lines
/road for surfaced roads
/dirt track for drivable dirt tracks
/paths for footpaths
The flags used are
/Entrance clear yellow circle size 3
/Sump clear blue circle size 3
/Swallet clear blue plus size 3
/Spring clear blue triangle size 3
/GPS fix clear red square size 3
/Lead clear red plus size 3
/Doline clear green plus size 3
The passage floor is in khaki (same as the /cave segment).