Abney Level

The Abney Level is an engineering instrument which can be used to determine height. It is

moderately expensive and of medium size and weight. Although the Abney Level is relatively

robust, the bubble tube can be knocked out of alignment during rough treatment.

When used correctly, the Abney Level has an accuracy of about +/- 0.5 m for a 20 m tall tree (ie

about 2.5%).

Use Measure the horizontal distance from the base of a vertical tree (or the position directly

beneath the tree tip of a leaning tree) to a location where the required point on the tree (e.g.

tree tip) can be seen.

Sight at the required point and move the index arm over the scale until the bubble tube is level.

Read the percentage scale (or the degrees and minutes of the angle).

Calculate the height by multiplying the percentage read by the horizontal distance (or by

multiplying the horizontal distance by Tan of the angle).

Topographic Abney Level

A Topographic Abney Level is an instrument used in surveying which consists of a fixed sighting

tube, a movable spirit level that is connected to a pointing arm, and a protractor scale. The

Topographic Abney Level is an easy to use, relatively inexpensive, and when used correctly an

accurate surveying tool. The Topographic Abney Level is used to measure degrees, percent of

grade, topographic elevation, and chainage correction. By using trigonometry the user of a

Topographic Abney Level can determine height, volume, and grade. The Topographic Abney

Level is used at the eye height of the surveyor and is best employed when teamed with a

second surveyor of the same eye height. This allows for easy sighting of the level and greater

accuracy. A ranging pole can be marked at the eye height of the level user or the approximate

location of the eye height (i.e. chin, nose, top of head) of the level surveyor must be know of

the ranging surveyor.

Site to the base of the tree and repeat steps 2 - 4.

Combine the heights from steps 4 and 5 to determine total tree height:

Add the 2 heights together if you looked up to the required point in step 2 and down to the

base of the tree in step 5.

Subtract the height to the base of the tree from the height to the required point if you are on

sloping ground and had to look up to both the required point and the base of the tree.

Origins

The Abney level was invented by Sir William de Wiveleslie Abney (Born 24 Jul 1843 Died 3 Dec

1920) who was an English astronomer and chemist best know for his pioneering of color

photography and color vision. Sir Abney invented this instrument under the employment of the

School of Military Engineering in Chatham, England in the 1870's. It is described by W. & L. E.

Gurley as an English modification of the Locke hand level, noting that it gives angles of elevation

and is also divided for slopes, as 1 to 2, 2 to 1, etc. Since the main tube of this instrument is

square, it can be applied to any plane surface. The clinometer scale is graduated to degrees,

and read by vernier to 5 minutes.

Usage

Use of an Abney level is discussed in volume 12 of the Forest Quarterly1 published by the New

York State College of Forestry in 1914. Discussion on the use of the Abney level starts on page

370.

To determine the elevation difference between you and a specific point

Point the sight at the selected point for which you wish to know the elevation difference and

view the location through the sight. Holding the Abney steady read the angle difference from

vertical off the side. Next measure the ground distance from you to the selected point using

paces or a measuring tape. To calculate the vertical elevation change use Equation 1.

Vertical Distance = Ground Distance X sin (angle) equation 1

To determine multiple locations with the same elevation

Point the sight at a point with a determined elevation, noting the angle difference from the

vertical. Move the Abney in any direction that does not change the angle measurement on the

side of the Abney level. Record all significant locations seen through the sight. These are all

landmarks with the same elevation equivalent to the starting position.

What is an Abney

A device used to determine elevation difference between an observer and a selected viewable

location. It is sometimes called an Abney level or clinometer. It works by measuring the angle

between an observer and a viewable point. The angle combined with the distance between the

observer and the viewable point can give the elevation difference with simple geometry. An

Abney is simple constructed, handheld, and easy to use and is therefore appropriate technology

for the developing world and people without access to other common surveying and mapping

tools. An Abney consists of viewing sight, a pendulum, and an angle scale shown in Figure 5.

How to Build an Abney

Materials

1. Sight The sight can be any tube like material such as a pipe or straw or a target

much like on a gun.

2. Angle Measure This can be a protractor, or anything with angle marking inscribed on it.

3. Pendulum This can be simply a string, wire, rope with a weight tied to one end.

Procedure

For this example I will use a straw as the sight, a piece of cardboard as the angle measure, and

string and a hex nut as the pendulum. This example is also described with pictures HERE but

should look similar to Figure 1.

1. Tape a piece of cardboard to the side of a drinking straw at one edge of the cardboard.

2. Punch a hole in the cardboard near the middle of the straw (and next to the straw) and tie a

string around the straw.

3. Tie a hex nut to the other end of the string, so that it hangs down from the center of the

straw and is below the cardboard.

4. Mark multiple angle measurements on the cardboard radiating out from the hole below the

straw.