Booking of the Field Data
Traversing involves taking bearings and distances from one station to the other until the last station is encountered. The survey book has two parallel lines running through the centre of each page. Booking is usually started from the last page of the book and from the bottom to the top of each page. The stations are represented as triangles enclosing serial numbers or letters specific to each station.
The bearing from A to B is recorded at the top of the triangle enclosing A. The distance from A to B is recorded at the base of the Triangle enclosing B. Any feature encountered, such as the footpath or the stream, is sketched at the point it crosses the survey line. Its distance from the previous station is recorded just below the sketch.
The Magnetic Declination; (MD), of the area of the survey is recorded at the bottom right hand corner, together with the date of completion of the survey and the names of the persons conducting the survey.
Indian Clinometer Survey
This is a simple instrument to measure the height of an object. Briefly explained, if you know the distance ab and the angle A, you can determine the length of side bc (or X). *Tangent is determined from a tangent chart.
Formula: ab x Tangent A = X Example: If ab = 36 feet
A = 35o x *Tan A = 0.7002 36 feet x 0.7002 = X
X = 25.2072 feet + Height of the man or height of the stole. *The height is approximately 25 feet.
An Example: Foresters Measure Trees the Smart Way
Calculating how much wood there might be in a forest is a bit like comparison shopping. Foresters do not count and measure every tree in the forest. That would simply take too long. Instead, they sample.
'We use sampling principles every day in our own lives,' says a Forester. If we're shopping for a stereo, he explains, we can't always check every price in every store. Instead, we sample a few brands and stores to get an estimate of what's available.
Similarly, foresters measure a few bits of the forest and, on the basis of those bits, estimate what the whole forest contains. Many of the techniques they use involve little more than careful measuring and some high-school mathematics. The first step is to choose which bits to sample. It is important to avoid picking samples that will give a false picture of the forest. The solution is to choose the sample plots randomly.
You could just throw darts at a map and sample where the darts land but affordable access is important. If your darts land well beyond the reach of roads, costs will soon eat up the sampling budget. Personal bias can be avoided by selecting locations on a map before going out in the field, rather than just walking through the forest and choosing good-looking trees. But once the locations are chosen, you have to stick with them, no matter what you find when you actually visit them.
'If one of your plots is in a clearing with very few trees, it is tempting to move it to an area with more trees. But you have to remember, that clearing represents lots of other clearings in the forest.' For biological studies, the most common approach to estimating the amount of wood is called a fixed area plot. The plots can be any shape, but all plots within a study must have exactly the same shape and dimensions. 'For estimating tree volume, fixed area plot size is chosen with the aim of including 12 to 20 trees.'
The next step is to measure the trees within the plot. Although the goal is to estimate volume, it is not easy to measure that directly without destroying the tree. Instead, you measure the tree's height and its diameter and use those two numbers to calculate the volume. You can determine the tree's height by using trigonometry. If you measure the horizontal distance between yourself and the tree, and measure the angles leading to the tree's top and base, you have enough information to calculate the tree's height. That is where you use the instrument called the Indian Clinometer.
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