Chapter 3 - Surveying

Table of Contents | Chapter 1 | Chapter 2 | Chapter 4 | Chapter 5

Cave Surveying Basics:

Cave Survey Gear:
Tape - preferably fiberglass
Compass & Clinometer - Suunto or Silva
Survey Book - weatherproof or waterproof
LED or flashlight - for illuminating the instruments while reading
Pencils - cheap mechanical ones
Protractor - small, cheap, plastic
Chalk, or flagging for marking stations.
Pulling Tape/Setting Stations:
The person on lead tape sets the survey stations and tries to maximize the survey shots. The placement of the survey stations must be carefully selected to accomodate the needs of the sketcher as well as the instrument reader. A poorly placed survey station can cause undo delays and hassles for the rest of the survey crew. The tape is used to measure the linear distance (D) between stations
Shooting Instruments:
In conjunction with the distance measurement, a bearing (compass reading) and a slope (clinometer reading) must be measured along the survey line to determine the coordinates of each survey station. By combining the distance, bearing and slope with a little trigonometry (on a computer of course), the three-dimensional location (X,Y,Z) of each survey station can be determined. These coordinates can be tied together and plotted graphically to represent the lines of the survey traverse.
The note-keeper/sketcher records all of the measurements, bearings, and slopes for later entry into a computer program. In addition, other data is recorded such as the distance to the cave walls at each station. Typically, this is done as "left, right, up, down", where a distance in feet from the survey station is estimated (or measured) in the four directions, roughly perpendicular to the line of the survey shot.
Probably the toughest part of cave surveying is keeping the sketch. Sketching requires a combination of skills that range from stenographer to drafter to artist. The role of the sketcher is to draw a rough representation of the cave passage along with relavent physical features in the cave. Such features may include: passage cross-sections, pits or drops, ceiling height changes, floor composition, streams, pools, upper/lower levels, formations, etc. All of this is usually drawn on a scaled line plot of the survey shots that is created on the fly in the sketcher's notebook. The use of graph paper, a ruler, and a protractor assist the sketcher in approximating the survey shots and cave passage orientation.

Advanced Techniques:

High Angle Shots  
Shifting the Station  
Backsights and Frontsights  
Splay Shots/Large Rooms or Passage  
Sketching in Very Wet or Muddy Conditions  

Reducing the Survey Data:

Cleaning up the Notes  
Entering the Data  
Identifying Errors  
Correction Techniques  
Loop Problems  

Plotting the Data: