Stockoscope - measure of diameter on standing trees above breast height

There are many older trees in our forests that, due to their age and size, represent
great values, both environmentally and economically, for the owner. 

Occasionally as forest farmers we get requests from sawmills and shipyards etc.
asking for trees with special demands on length, diameter and quality.
Such special products are sold at higher prices.

The forest farmer has an  interest in only cutting down trees that fulfil the
required specifications. It is simple to measure height and determine quality
but when it comes to diameters high above and beyond one's reach, it is 
more complicated to be sure to meet the specifications of the customer. 

The Stockoscope is used to measure upper diameter (top end diameter)
or log mid point diameter.

The theory of the Stockoscope is carefully described and explained in the manual 
"Stokoskopi - Diametermåling på stående træer i valgfri højde". 
The manual is in Danish and has not been translated into English.
                                                                                                                      
The upper diameter can be calculated by combining the measurements of distance, 
tree height and diameter. A Suunto Dendrometer is used for height measurements.
The distance can be measured with either measurement band or distance prism and
surveyor's staff.
The diameter is measured indirectly by using a slide caliper with a chain as a relascope.

The Stockoscope is in fact a relascope with an adjustable slit, with which You can make
a "reversed" relascope measurement. 

By combining geometry with statistics it is  possible to calculate the upper diameter and
log volume within a few percent of true values.

Instruction                                                      

A. Measuring of top end or log mid point diameter

1. Consider  the presence of any inclination of the tree and if the sectional area 
   has an oval form. Estimate the number of measures to be made (1 - 4, see 
   manual:  ILYX - measurements and limit of error). Make the same number of 
   marks in eye height, divided equally around the stem and under consideration 
   of the form. Estimate the stump height after felling.
2. Make a calibration of the instrument and Your self.  It is done by following points 3 - 7 
   and measure the tree diameter in eye height. The calculated diameter should not 
   diverge more than 2 - 3 % from the measured diameter.
3. The measuring band is placed 10 - 20 cm above ground level in the vertical plump 
   line of the Stockoscope measuring point. The band is normally fastened to the tree. 
   Where the vertical plump line is situated beside the tree due to inclination, the 
   band is fastened to the ground. Walk 15 meters away from the tree and mark the 
   spot on the ground for the Stockoscope readings. 
4. The values for eye mark, root and top end or mid point are made with a Suunto   
   Dendrometer.
5. The Stockoscope readings are taken from the same position (important!) 
6. Points 3 - 5 are repeated from the positions in the same distance from the tree 
   (I: 1 measurement, L: 2 measurements 90º, Y: 3 measurements 120º or 
   X: 4 measurements 90º).
7. Use the spreadsheet to find the average of the measurements.
   

B. Looking for a certain top end or log mid point diameter   

1. Determine the over measure with help from the spreadsheet and calculate the 
   adjustment of the Stockoscope. 
2. If the tree stand is situated on flat ground You can use the diagram from the 
   spreadsheet. On slopes You have to calculate by using the spreadsheet on a laptop.
3. Calibrate the instrument as shown above (A 2 - 7).
4. Find the distance: 15 meters, by using the measure band.
5. With the Dendrometer, find the spot where the wanted diameter is situated.
6. Adjust the Stockoscope to the calculated value of upper diameter and measure 
   the tree. If the tree diameter is less than the Stockoscope slit, the tree is to small. 
   Continue to the next tree. Else repeat the measurement of the diameter 1 - 3 times 
   to be sure of the result.

© Copyright Truls Wiberg 2001

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Skov- og landskabsingeniør

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