Forest Measurement and Modelling.
The Spiegel Relaskop, also known as a Relaskop, is a sophisticated instrument that can be used to measure stand basal area and tree height and diameter at any point up a tree bole. In conjunction with other equipment, the Relaskop can be used in the estimation of distance (range) to an object and the number of trees / ha.
The Relaskop has a peep-hole at the rear and a clear window at the front. Three additional windows in the lower half of the instrument allow light to enter and illuminate the scale. A brake button, bottom half at the front of the instrument, allows a weighted wheel within the Relaskop to rotate. When looking through the peephole, a circular field of view is seen. The scales are seen in the bottom half of this field of view and scale readings are taken where the scale touches the line halfway up the field of view.
The standard metric Relaskop has three scales for measuring (vertical) height. The appropriate scale will depend on the horizontal distance from the tree.
If you depress the brake button and look straight up or down, the appropriate distance values can be seen alongside their scales.
Select a point that is 10 to 60 m (horizontal) from the tree of interest. The base and tip (or any other points of interest) must be clearly visible from the selected point. If the tree is leaning, the point where you observe the tree should be at 90 degrees to the plane of the lean. If the lean is severe (i.e. more than 10 degrees from vertical), the point directly beneath the tip of the tree should be located (e.g. using a pumb-bob) and the horizontal distance taken from this point. The actual distance chosen is related to an initial estimate of the tree height:
Once the observation point is found and the appropriate scale selected, sight through the peephole to the base of the tree. Tap the brake button several times until the scale settles then read the height directly from the appropriate scale. If you are looking down towards the base of the tree, this reading is the vertical height that the base of the tree is beneath your eye. Sight to the top of the tree (or other point) and again tap the brake button until the scale settles. The scale is a direct reading of the height above your eye to this new point. Add the two heights together if the base of the tree was below your eye to determine total (vertical) height. If the base of the tree was initially above your eye (i.e. the base if above you on sloping ground) subtract the initial height from the upper height to determine (vertical) height.
Height is determined (and recorded) to the nearest quarter metre (0, 1/4, 1/2, 3/4 m) for trees less than 20 m, or to the nearest half metre (0, 1/2 m) for trees greater than 20 m.
The band labelled with "1" and the four narrow (or quarter) bands along side are used to estimate diameter.
To determine the bole diameter for a known height on the tree:
To measure both height and diameter at one or more points up the stem:
Note that the above approaches only measure diameter along one axis of the bole. If the bole is elliptical, this measurement will over- or under-estimate the average diameter. The diameter measurement could be repeated at 90 degrees, but this is rarely carried out in practice.
|Stand basal area||
The Relaskop can generate nine basal area factors (BAFs) using bands 1, 2 and combinations of the quarter bands:|
|Band 1 + 1 quarter||1.5625||(25/16)|
|Band 1 + 2 quarters||2.25||(36/16)|
|Band 1 + 3 quarters||3.0625||(49/16)|
| Band 1 + 4 quarters |
Also called Band 4
Choose the appropriate BAF and combination of bands. Then, standing over the sample point, hold the brake button down and make a sweep of 360 degrees while comparing the tree diameters at breast height with the selected bands. Count the number of trees whose diameter at breast height appears greater (wider) than the selected bands - IN trees. Ensure trees are not hidden behind closer trees by stepping to one side and checking before returning to the sample point. Where trees appear to be the same width as the selected Relaskop bands, or it is not obvious that the tree diameter is larger, measure the distance to the tree and that tree dbh and refer to the borderline calculations. Once the sweep has been completed, multiply the count of IN trees by the appropriate BAF to get stand basal area (m^2/ha).
[relaskop.htm] Revision: 6/1999