The surveyor measures from the survey station to the first knot on the line, then swims along the line adding 10 feet (3m) for every knot he passes, then measures from the final knot to the next survey station. Such line typically has knots every 10 feet (3m). The first is to use knotted cave line when exploring a cave. Most surveyors in Mexico use one of two quick and reasonably accurate methods. In reality, these methods are often more cumbersome and time consuming than they are worth, and laser or sonar measuring devices do not always work well in caves with heavy percolation. In an ideal situation, divers would use measuring tape or an electronic measuring device to get a highly accurate reading.
Measuring the distance between survey points can also be source of error. If the cave line is poorly laid, bending around or over rocks and cave features, the compass heading will not represent the azimuth of the entire line, and will affect the survey’s accuracy. The angle at which a surveyor views the compass, how steadily he holds it, and which eye he looks though will all affect the accuracy of the compass reading. Analog compasses must be held perfectly flat, and most serious surveyors have a small bubble level glued to their compass or survey slate to help.
Digital depth gauges make the depth measurement highly accurate however, the compass and distance measurements are subject to quite a bit of error. This process is trickier than it may sound. He then measures the length from between the current station and the next, and records the data on slate or notebook. At each tie off along the line (or survey station), the diver records the depth at the line and the compass heading to the next station. A cave surveyor uses a method of measuring distance, along with compass and depth gauge, to create his survey. The creation of a cave survey is straight forward, but accuracy takes practice. For many explorers including myself, the mapping process stops with the basic survey. This is a graphic representation of the cave line with no detail about the walls or cave features. The first step of creating a map is called the survey, or ‘stick map’. Creating a map is a great deal more work than one might think, and it’s a multistep process. I am not an underwater cartographer, but I know a few, and I am impressed with their level of commitment and drive. A cartographer must achieve a balance between the level of detail and the ‘big picture’ overview to create a usable map for cave divers. Photo: Cyril BuchetĪ well-made map of an underwater cave is a beautiful thing. An excellent skills set, accuracy, dedication and little pot of money are required to make a good cave map.
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