Cave survey
Encyclopedia
A cave survey is a map
of all or part of a cave
system, which may be produced to meet differing standards of accuracy depending on the cave conditions and equipment available underground. Cave surveying and cartography
, i.e. the creation of an accurate, detailed map, is one of the most common technical activities undertaken within a cave and is a fundamental part of speleology
. Surveys can be used to compare caves to each other by length, depth and volume, may reveal clues on speleogenesis
, provide a spatial reference for other areas of scientific study and assist visitors with route-finding.
Traditionally, cave surveys are produced in two-dimensional form due to the confines of print, but given the three-dimensional environment inside a cave, modern techniques using computer aided design are increasingly used to allow a more realistic representation of a cave system.
near Naples
in Italy. The first natural cave to be mapped was the Baumannshöhle
in Germany
, of which a sketch from 1656 survives.
Another early survey dates from before 1680, and was made by John Aubrey
of Long Hole in the Cheddar Gorge. it consists of a elevational section of the cave. Numerous other surveys of caves were made in the following years, though most are sketches and are limited in accuracy. The first cave that is likely to have been accurately surveyed with instruments is the Grotte de Miremont in France
. This was surveyed by a civil engineer in 1765 and includes numerous cross-sections. Édouard-Alfred Martel
was the first person to describe surveying technique. His surveys were made by having an assistant walk down the passage until they were almost out of sight. Martel would then take a compass bearing to the assistant's light, and measure the distance by pacing up to the assistant. This would equate to a modern day BCRA Grade 2 survey.
The first cave to have its centreline calculated by a computer is the Fergus River Cave in Ireland
, which was plotted by members of the UBSS in 1964. The software was programed onto a large university mainframe computer and a paper plot was produced.
The measurements taken between the stations include:
Coincident with recording straight-line data, details of passage dimensions, shape, gradual or sudden changes in elevation, the presence or absence of still or flowing water, the location of notable features and the material on the floor are recorded, often by means of a sketch map.
calculations. From them he/she creates a line-plot; a scaled geometrical representation of the path through the cave.
on the Arabica Massif in the Caucasus
—currently the world's deepest cave.
The hydrolevel device used in recent Voronja expeditions comprises a 50 metres (164 ft) transparent tube filled with water, which is coiled or placed on a reel. A rubber glove which acts as a reservoir is placed on one end of the tube, and a metal box with a transparent window is placed on the other. A diver's digital wristwatch with a depth gauge function is submerged in the box. If the rubber glove is placed on one station and the box with the depth gauge is placed on a lower one, then the hydrostatic pressure between the two points depends only on the difference in heights and the density of the water, i.e. the route of the tube does not affect the pressure in the box. Reading the depth gauge gives the apparent depth change between the higher and lower station. Depth changes are 'apparent' because depth gauges are calibrated for sea water, and the hydrolevel is filled with fresh water. Therefore a coefficient must be determined to convert apparent depth changes to true depth changes. Adding the readings for consecutive pairs of stations gives the total depth of the cave.
in the 1960s, which uses a scale of six grades.
Grade 2 (use only if necessary, see note 7)
Grade 3
Grade 4 (use only if necessary, see note 7)
Grade 5
Grade 6
Grade X
Class B
Class C
Class D
Despite these advances, faulty instruments, imprecise measurements, recording errors or other factors may still result in an inaccurate survey, and these errors are often difficult to detect. Some cave surveyors measure each station twice, recording a back-sight to the previous station in the opposite direction. A back-sight compass reading that is different by 180 degrees and a clinometer reading that is the same value but with the reverse direction (positive rather than negative, for example) indicates that the original measurement was accurate.
When a loop within a cave is surveyed back to its starting point, the resulting line-plot should also form a closed loop. Any gap between the first and last stations is called a loop-closure error. If no single error is apparent, one may assume the loop-closure error is due to cumulative inaccuracies, and cave survey software can 'close the loop' by averaging possible errors throughout the loop stations. Loops to test survey accuracy may also be made by surveying across the surface between multiple entrances to the same cave.
The use of a low-frequency cave radio can also verify survey accuracy. A receiving unit on the surface can pinpoint the depth and location of a transmitter in a cave passage by measurement of the geometry of its radio waves. A survey over the surface from the receiver back to the cave entrance forms an artificial loop with the underground survey, whose loop-closure error can then be determined.
In the past, cavers were reluctant to redraw complex cave maps after detecting survey errors. Today, computer cartography can automatically redraw cave maps after data has been corrected.
A popular program for producing a centerline survey is Survex
, which was originally developed by members of the Cambridge University Caving Club for processing survey data from club expeditions to Austria
. It was released to the public in 1992. The centerline data can then be exported in various formats and the cave detail drawn in with various other programmes such as AutoCAD
, Adobe Illustrator
and Inkscape
. Other programmes such as Tunnel and Therion
have full centerline and map editing capabilities. Therion notably, when it closes survey loops, warps the passages to fit over their length, meaning that entire passages do not have to be redrawn.
has been utilized in the mining
industry. The technology utilizes a gyroscope
and an accelerometer
to aid in 3D-position determination.
Such automated methods have provided a more than fifty-fold increase in underground surveying productivity with more accurate and finer detail maps as well.
Map
A map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes....
of all or part of a cave
Cave
A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also includes smaller spaces like rock shelters, sea caves, and grottos.Speleology is the science of exploration and study...
system, which may be produced to meet differing standards of accuracy depending on the cave conditions and equipment available underground. Cave surveying and cartography
Cartography
Cartography is the study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.The fundamental problems of traditional cartography are to:*Set the map's...
, i.e. the creation of an accurate, detailed map, is one of the most common technical activities undertaken within a cave and is a fundamental part of speleology
Speleology
Speleology is the scientific study of caves and other karst features, their make-up, structure, physical properties, history, life forms, and the processes by which they form and change over time...
. Surveys can be used to compare caves to each other by length, depth and volume, may reveal clues on speleogenesis
Speleogenesis
Speleogenesis is the origin and development of caves, the primary process that determines essential features of the hydrogeology of karst and guides its evolution...
, provide a spatial reference for other areas of scientific study and assist visitors with route-finding.
Traditionally, cave surveys are produced in two-dimensional form due to the confines of print, but given the three-dimensional environment inside a cave, modern techniques using computer aided design are increasingly used to allow a more realistic representation of a cave system.
History
The first known plan of a cave dates from 1546, and was of a man-made cavern in tufa called the Stufe di Nerone (Nero's Oven) in PozzuoliPozzuoli
Pozzuoli is a city and comune of the province of Naples, in the Italian region of Campania. It is the main city of the Phlegrean peninsula.-History:Pozzuoli began as the Greek colony of Dicaearchia...
near Naples
Naples
Naples is a city in Southern Italy, situated on the country's west coast by the Gulf of Naples. Lying between two notable volcanic regions, Mount Vesuvius and the Phlegraean Fields, it is the capital of the region of Campania and of the province of Naples...
in Italy. The first natural cave to be mapped was the Baumannshöhle
Baumann's Cave
Baumann's Cave is, like nearby Hermann's Cave, a show cave in Rübeland in the district of Harz and is Germany's oldest show cave.The grotto was formed in the Devonian limestone of the Elbingerode complex as the Bode Valley was being shaped. It was discovered in the 16th century and was...
in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, of which a sketch from 1656 survives.
Another early survey dates from before 1680, and was made by John Aubrey
John Aubrey
John Aubrey FRS, was an English antiquary, natural philosopher and writer. He is perhaps best known as the author of the collection of short biographical pieces usually referred to as Brief Lives...
of Long Hole in the Cheddar Gorge. it consists of a elevational section of the cave. Numerous other surveys of caves were made in the following years, though most are sketches and are limited in accuracy. The first cave that is likely to have been accurately surveyed with instruments is the Grotte de Miremont in France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. This was surveyed by a civil engineer in 1765 and includes numerous cross-sections. Édouard-Alfred Martel
Édouard-Alfred Martel
, the 'father of modern speleology', was a world pioneer of cave exploration, study, and documentation...
was the first person to describe surveying technique. His surveys were made by having an assistant walk down the passage until they were almost out of sight. Martel would then take a compass bearing to the assistant's light, and measure the distance by pacing up to the assistant. This would equate to a modern day BCRA Grade 2 survey.
The first cave to have its centreline calculated by a computer is the Fergus River Cave in Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
, which was plotted by members of the UBSS in 1964. The software was programed onto a large university mainframe computer and a paper plot was produced.
Methodology
There are many variations to surveying methodology, but most are based on a similar set of steps.Surveying
A survey team begins at a fixed point (such as the cave entrance) and measures a series of consecutive line-of-sight measurements between stations. The stations are temporary fixed locations chosen chiefly for their ease of access and clear sight along the cave passage. In some cases, survey stations may be permanently marked to create a fixed reference point to which to return at a later date.The measurements taken between the stations include:
- direction (azimuth or bearing) taken with a compassCompassA compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...
- inclination from horizontal (dip) taken with a clinometer
- distance measured with a low-stretch tape or laser rangefinder
Coincident with recording straight-line data, details of passage dimensions, shape, gradual or sudden changes in elevation, the presence or absence of still or flowing water, the location of notable features and the material on the floor are recorded, often by means of a sketch map.
Drawing a line-plot
Later, the cartographer analyses the recorded data, converting them into two-dimensional measurements by way of geometricalGeometry
Geometry arose as the field of knowledge dealing with spatial relationships. Geometry was one of the two fields of pre-modern mathematics, the other being the study of numbers ....
calculations. From them he/she creates a line-plot; a scaled geometrical representation of the path through the cave.
Finalising
The cartographer then draws details around the line-plot, using the additional data of passage dimensions, water flow and floor/wall topography recorded at the time, to produce a completed cave survey. Cave surveys drawn on paper are often presented in two-dimensional plan and/or profile views, while computer surveys may simulate three dimensions. Although primarily designed to be functional, some cavers consider cave surveys as an art form.Hydrolevelling
Hydrolevelling is an alternative to measuring depth with clinometer and tape that has a long history of use in Russia. The technique is regularly used in building construction for finding two points with the same height, as in levelling a floor. In the simplest case, a tube with both ends open is used, attached to a strip of wood, and the tube is filled with water and the depth at each end marked. In Russia, measuring the depth of caves by hydrolevelling began in the 1970s, and was considered to be the most accurate means of measuring depth despite the difficulties in using the cumbersome equipment of the time. Interest in the method has been revived following the discovery of VoronjaVoronya Cave
The Krubera Cave is the deepest known cave on Earth. It is located in the Arabika Massif of the Gagrinsky Range of the Western Caucasus, in the Gagra district of Abkhazia, Georgia’s breakaway republic.The difference in the altitude of the cave's entrance and its deepest explored point is...
on the Arabica Massif in the Caucasus
Caucasus
The Caucasus, also Caucas or Caucasia , is a geopolitical region at the border of Europe and Asia, and situated between the Black and the Caspian sea...
—currently the world's deepest cave.
The hydrolevel device used in recent Voronja expeditions comprises a 50 metres (164 ft) transparent tube filled with water, which is coiled or placed on a reel. A rubber glove which acts as a reservoir is placed on one end of the tube, and a metal box with a transparent window is placed on the other. A diver's digital wristwatch with a depth gauge function is submerged in the box. If the rubber glove is placed on one station and the box with the depth gauge is placed on a lower one, then the hydrostatic pressure between the two points depends only on the difference in heights and the density of the water, i.e. the route of the tube does not affect the pressure in the box. Reading the depth gauge gives the apparent depth change between the higher and lower station. Depth changes are 'apparent' because depth gauges are calibrated for sea water, and the hydrolevel is filled with fresh water. Therefore a coefficient must be determined to convert apparent depth changes to true depth changes. Adding the readings for consecutive pairs of stations gives the total depth of the cave.
Accuracy
The accuracy, or grade, of a cave survey is dependent on the methodology of measurement. A common survey grading system is that created by the British Cave Research AssociationBritish Cave Research Association
The British Cave Research Association is a speleological organisation in the United Kingdom. Its object is to promote the study of caves and associated phenomena, and it attains this by supporting cave & karst research, encouraging original exploration , collecting and publishing speleological...
in the 1960s, which uses a scale of six grades.
BCRA gradings for a cave line survey
Grade 1- Sketch of low accuracy where no measurements have been made
Grade 2 (use only if necessary, see note 7)
- 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 ±2.5 º; distances measured to ±50 cm; station position error less than 50 cm.
Grade 4 (use only if necessary, see note 7)
- 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 ±1 º; distances should be observed and recorded to the nearest centimetre and station positions identified to less than 10 cm.
Grade 6
- A magnetic survey that is more accurate than grade 5, (see note 5).
Grade X
- A survey that is based primarily on the use of a theodolite or total station instead of a compass, (see notes 6 and 10 below).
BCRA gradings for recording cave passage detail
Class A- All passage details based on memory.
Class B
- Passage details estimated and recorded in the cave.
Class C
- Measurements of detail made at survey stations only.
Class D
- Measurements of detail made at survey stations and wherever else needed to show significant changes in passage dimensions.
Survey error detection
The equipment used to undertake a cave survey continues to improve. The use of computers, inertia systems, and electronic distance finders has been proposed, but few practical underground applications have evolved at present.Despite these advances, faulty instruments, imprecise measurements, recording errors or other factors may still result in an inaccurate survey, and these errors are often difficult to detect. Some cave surveyors measure each station twice, recording a back-sight to the previous station in the opposite direction. A back-sight compass reading that is different by 180 degrees and a clinometer reading that is the same value but with the reverse direction (positive rather than negative, for example) indicates that the original measurement was accurate.
When a loop within a cave is surveyed back to its starting point, the resulting line-plot should also form a closed loop. Any gap between the first and last stations is called a loop-closure error. If no single error is apparent, one may assume the loop-closure error is due to cumulative inaccuracies, and cave survey software can 'close the loop' by averaging possible errors throughout the loop stations. Loops to test survey accuracy may also be made by surveying across the surface between multiple entrances to the same cave.
The use of a low-frequency cave radio can also verify survey accuracy. A receiving unit on the surface can pinpoint the depth and location of a transmitter in a cave passage by measurement of the geometry of its radio waves. A survey over the surface from the receiver back to the cave entrance forms an artificial loop with the underground survey, whose loop-closure error can then be determined.
In the past, cavers were reluctant to redraw complex cave maps after detecting survey errors. Today, computer cartography can automatically redraw cave maps after data has been corrected.
Surveying software
There is a large number of surveying packages available on various computer platforms, most of which have been developed by cavers with a basis in computer programming. Many of the packages perform particularly well for specific tasks, and as such many cave surveyors will not solely choose one product over another for all cartographic tasks.A popular program for producing a centerline survey is Survex
Survex
Survex is an open source cave surveying software package, licensed under the GPL. It is designed to be portable and can be run on a variety of platforms, including Microsoft Windows, Mac OS X, and Unix...
, which was originally developed by members of the Cambridge University Caving Club for processing survey data from club expeditions to Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...
. It was released to the public in 1992. The centerline data can then be exported in various formats and the cave detail drawn in with various other programmes such as AutoCAD
AutoCAD
AutoCAD is a software application for computer-aided design and drafting in both 2D and 3D. It is developed and sold by Autodesk, Inc. First released in December 1982, AutoCAD was one of the first CAD programs to run on personal computers, notably the IBM PC...
, Adobe Illustrator
Adobe Illustrator
Adobe Illustrator is a vector graphics editor developed and marketed by Adobe Systems. Illustrator is similar in scope, intended market, and functionality to its competitors, CorelDraw, Xara Designer Pro and Macromedia FreeHand....
and Inkscape
Inkscape
Inkscape is a free software vector graphics editor, licensed under the GNU General Public License. Its goal is to implement full support for the Scalable Vector Graphics 1.1 standard....
. Other programmes such as Tunnel and Therion
Therion (software)
Therion is a open source cave surveying software package designed for the purpose of drawing cave maps and archiving the data describing the cave.-Description:...
have full centerline and map editing capabilities. Therion notably, when it closes survey loops, warps the passages to fit over their length, meaning that entire passages do not have to be redrawn.
Automated methods
In recent years an underground geographic positioning technology called HORTAHORTA (mining)
HORTA is an underground geographic positioning technology utilized in the mining industry and being considered for extraterrestrial space mining applications...
has been utilized in the mining
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
industry. The technology utilizes a gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...
and an accelerometer
Accelerometer
An accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...
to aid in 3D-position determination.
Such automated methods have provided a more than fifty-fold increase in underground surveying productivity with more accurate and finer detail maps as well.
External links
- Compass Points, the official journal of the BCRA Cave Surveying Group
- CaveMaps.org Surveys, A collection of Surveys of British Caves