Relaskop / Spiegel Relaskop ©

An sophisticated, compact and robust but expensive instrument for measuring height, diameter, basal area and range. Has a variety of scales for the different uses.

Height measurement

There are three height scales (20, 25 and 30 m) on the standard metric version. (The wide angle Spiegel relaskop has a larger number of height scales). All the height scales are visible when sighting but they are not identified.

General instruction for use of the Relaskop for measuring height:

  1. Measure the desired horizontal distance from the base of the tree (or point directly beneath the tree tip) to a location where the required point (eg tree tip) can be seen;
  2. Sight at the required point, while holding the break button to allow the scales to freely rotate;
  3. Read the height from the appropriate scale once the scale has settled. Tapping and releasing the break button can help the scales to settle more quickly;
  4. Sight to the base of the tree and repeat the above two steps;
  5. Add the heights together to get total tree height
Comparison with other instruments

Diameter measurement

General instruction for use of the Relaskop for measuring diameter:
  1. Measure the desired horizontal distance (H metres) from the base of the tree (or point directly beneath the desired tree site) to a location where the required point (eg change in diameter) can be seen. Note that you must be at least 5 m away for every 20 cm anticipated diameter;
  2. Sight at the required point, while holding the break button to allow the scales to freely rotate;
  3. Read from the diameter scale once the scale has settled the number of large bands (with the number 1 printed on them) (L); the number of small bands (4 narrow bands immediately to the right of the large 1 band) (S); and an estimate of any fractional small band (s). Estimate the fractions of the small band as 0.2 (just into the band), 0.4 (almost half), 0.6 (just over half), 0.8 (amost full narrow band).
  4. Diameter is calculated as d (cm) = H*(L+0.25*(S+s))*2;
  5. Check to ensure the diameter appears correct. Note that L will be 0 or 1, S will be 0, 1, 2, 3, 4 and s will be a fraction less than 1.0.
If the sample tree above were 20 m away, the diameter would be: 
d (cm) = 20 * (1+0.25*(3+0.2)) * 2
           = 72 cm
Comparison with other instruments

Measuring Basal Area with the Relaskop

The original instrument of BITTERLICH was called a RELASKOP. It comprised a 1 metre rod with a 2 cm wide opaque blade mounted at one end at right angles to the rod axis - this generated the reference angle.

Disadvantages of Relaskop

These disadvantages become most apparent in use in the approximate BORDERLINE situation, i.e. the situation where the reference angle and the angle subtended by the tree are about the same.

Bitterlich, over the years, has repeatedly modified the original Relaskop. The latest model is a compact, multipurpose instrument called the SPIEGEL RELASKOP which can be used to measure tree height, stand height, tree diameter at any height from ground, stand basal area, and miscellaneous other tree/stand parameters.

The Spiegel Relaskop incorporates reflected scale images which allow a choice of as many as nine basal area factors. Through an adjustment of the calibration on the internal scale, the instrument automatically corrects for slope.

However, the disadvantages of the original Relaskop still apply to the latest Spiegel Relaskop.

Calibration checks

Checking Doubtful Trees when Angle Counting using Bitterlich's Spiegel Relaskop

(Also see Wood, G.B. 1982. Checking borderline trees by Spiegel Relaskop. Aust. For. 45(1):57-8).

Bitterlich's Spiegel Relaskop is a most versatile instrument for forest measurement. It is particularly useful and efficient for estimating stand basal area per unit area but has the disadvantage that it cannot establish precisely whether doubtful trees are in, out or truly borderline. Such cases occur on average in about 10% of the trees counted in an angle count sweep.

Precise estimation of stand basal area by Relaskop requires that all doubtful trees be checked by direct measurement. Checking is complicated by the fact that efficient use of the Relaskop requires the brake to be freed which corrects automatically for slope. This must be allowed for in calculating limiting or borderline slope distances.

The ready availability today of pocket calculators enables limiting slope distances for doubtful trees to be calculated quickly in the field using the formula:

Limiting slope distance (metres) = d (cm) x Sec ÿ x K

where d is dbhob, preferably measured by caliper at right angles to the line of sight from the observer.

and ÿ is the angle of slope from the observer's eye to the breast height mark.

Values of K for the nine bands or band combinations of the standard metric relaskop are presented in Table. Comparison of the calculated limiting slope distance with the measured slope distance then determines whether the doubtful tree is in, out or truly borderline.

K values for determining limiting distances when sweeping by standard Spiegel Relaskop with the brake freed.

             BAND                 BAF       K
          1 narrow band (NB)     0.0625     2
          2 NB                   0.25       1
          3 NB                   0.5625     0.6
          1                      1.0        0.5
          1 + 1 NB               1.5625     0.4
          1 + 2 NB               2.25       0.3
          1 + 3 NB               3.0625     0.2857
          2                      2.0        0.3536
          4                      4.0        0.25



Derivation of K:


BAF = 2500 (d/D)^2 /10 000,      where d is dbhob (cm) and D is the limiting distance (m).


In the true borderline situation, d/D is constant.  Hence D = d.K.  


Substituting for D in the equation, we have: 


K = 0.5/_BAF.





Dr Walter Bitterlich, who pioneered this approach, sees a  bright future for futher enhancement of the Relaskop. See his articles:




Index    Help    Authors 






Document URLhttp://online.anu.edu.au/Forestry/mensuration/RELAKOP.HTM

 Editor Cris Brack ©

Last Modified DateFri, 9 Feb 1996