Using an Electronic Relaskop / Dendrometer for Variable Plot Cruising

and Measuring Form of Trees

Laser Technology, Inc. (LTI)(http://www.lasertech.com)

Bill Carr

2nd International Conference on Forest Measurements and Quantitative

Methods and Management - June 2004

Explanation of Terms

Variable Plot Sampling – Variable Point Sampling – Point Sampling – Angle Count Sampling (ACS) – Bitterlich Sampling – Sample tree selection frequency is based on a probability proportional to basal area (size). Tree selection is made by using an instrument that permits the cruiser to visually project a predetermined angle.

Relascope – An instrument for measuring horizontal angles and has automatic adjustment for slope from the instrument to DBH.

Dendrometer – An instrument designed to estimate the diameters of standing trees at any given height by sighting from the ground.

Brief History of Angle Projection Instrumentation

Cross-staff – 1947*

Prism - 1948

Angle Gauge - 1948Pendelrelaskop – 1949*

Spiegelrelaskop - 1950 Criterion - 1992*The Relascope Idea, Walter Bitterlich,1984, pg.70. *The Relascope Idea, Walter Bitterlich,1984, pg.81.

Limitations of these Instruments

Cross-staff to various angle gauges – The primary limitation is that slope corrections are prone to errors. Also, construction and wear often changes the distance the gauge is held from the eye (apex of the critical angle). Also, they can utilize only fixed BAF’s.

Prisms – Slope correction is made by rotating the prism, but if improperly done it changes the BAF. Prisms have a limited number of BAF’s.

Spiegelrelaskop – Misreading of scales causes errors in selection of sample trees, difficulty in reading scales in dim light conditions and the instrument is mechanical which makes it subject to wear and false correction for slope.

Criterion – Heavy, expensive and requires reading a scale which is difficult to read. Also, it’s no longer manufactured.

Consequences

There are Two Primary Consequences:

1. Errors in Number of Trees Selected on the Point

A. Each tree missed or added in error represents several trees/acre. A 10-inch tree on a 40 BAF cruise represents 73 trees per acre.

B. If tree attributes, such as value, DBH, defect, etc. are computed from the cruise it has a compounding effect.

2. Inefficiency

A. More time and care must be taken to prevent errors in selection.

B. More “questionable” trees will need to be measured.

Brief History of Dendrometer

InstrumentationBarr & Stroud - 1945

Relascope - 1950 Telerelascope – 1972*

Criterion - 1992

*The Relascope Idea, Walter Bitterlich,1984, pg. 93.

Limitations of These Dendrometers

The greater the accuracy the greater the expense ( $1,200 - $15,000 )

Have to read vernier, reticule or rotating scales to interpret diameters.

The greater the accuracy the greater the weight.

The Barr & Stroud and Criterion are no longer manufactured.

Challenge

Develop an instrument that would:

A. Function as a relascope and dendrometer.

B. Be accurate

C. Provide direct readout of diameters and heights

D. Be a stand alone instrument or capable of being connected to range finders or data recorders through serial ports.

E. Be user friendly for several applications.

F. Be light weight and small (cruiser vest friendly).

G. Be inexpensive.

Development – Alpha Unit

In 2003, four Alpha test units were manufactured with off the shelf components to evaluate the concept of making an electronic relascope / dendrometer.

Used as a stand alone instrument

Connected to an Impulse laser rangefinder and data recorder to download concatenated data

Alpha Evaluation Results

The optical solutions, heads-up display and firmware solutions were very successful. Being an Alpha unit there were some shortcomings. It was too big, too heavy, not as accurate as needed (+1-inch at 80 feet) and not as user friendly as needed.

Development – Beta Unit

Beta Unit Specifications

Dimensions: 2.75”W x 2.00”D x 6.5”L

Weight: 1.1 lbs.

Inclination measurement range: +90o

Inclination accuracy: +0.1o

BAF range: 1 to 134 ft.2/acre

Diameter range: 5” to 44” @ 80 feet (with magnifying lens attached)

Diameter accuracy: +0.25 inch @ 80 feet (with magnifying lens)

Height accuracy: +0.1 feet

Environmental: IP54 (waterproof)

Temperature: -30 to +60oC operating

Beta Unit Features

Keypad: 9-key, silicone rubber, LED backlit

Main Display: Backlit, custom LCD

Heads-up Display: Custom, projection LED, 4-digit, 7 segment, 114 segment diameter scale

Data communications: 2X, RS-232 serial data ports,Bi-directional, ASCII hex data interchange Compatible with LTI laser data output

Power: Internal, replaceable batteries – 2 ea. “AA” (alkaline, NiMh, LiInS2), or 1 ea. CRV3 (Li)

Optics: Relascope – zero magnification

Dendrometer – detachable 2.4X lens

Keypad

HUD – The heads-up display button is used to change the brightness of the display and to change the bar scale from ‘solid’ to ‘gap’.

Modes of Operation

5 Operating Modes:

SYSTEM – Used to set operating parameters

BAF – Used to store the Basal Area Factor (BAF)

IN / OUT – Used to determine if a “questionable” tree is “in” or “out” of the plot.

DIAMETER – Used to determine the diameter of a tree at a given height up the tree.

HEIGHT / DIAMETER – Used to determine the height up the tree at which a specific diameter is reached.

Full LCD

SYSTEM Mode

MAG: Used to let the instrument know if the magnifying lens is attached and to set the unique magnification constant for the specific lens.

UNITS: To set the instrument to Metric or Imperial units of measurement

DEG: To set the inclination sensor calibration and zero offset function.

SYSTEM Mode

Full LCD DisplaySYSTEM – UNITS

Display

BAF 20

BAF – (Basal Area Factor)

LCD HUD

Measurement bar length adjusted for slope

IN / OUT Trees

Enter DBH either by measuring with the instrument (in DIAMETER mode) or manually

Enter horizontal distance from plot center (instrument) to the face of the tree at DBH manually or automatically with Impulse laser

Press ENTER and the LCD and HUD will indicate if the tree is “IN” or “OUT” of the plot

DIAMETER Mode1. Enter the horizontal distance from the instrument to the face-of-the-tree at the point where the diameter is to be measured or shoot to that point with an Impulse laser and it will automatically load that value.

2. Aim at the base of the tree, press and release the trigger – the display will show degrees to the base of the tree.

3. Press the trigger and scan up the tree to where you want to measure the diameter. The HUD and LCD will display, in dynamic mode, the height as the instrument scans up the tree.

4. The position will be locked each time the trigger is released and the bar can be adjusted to the tree width. As the bar is adjusted the representative diameter will be displayed.

5. Press ENTER to transmit to a data recorder.

6. Repeat steps 3 through 5 as often as desired.

DIAMETER Mode

Bar set to GAP / Display shows HEIGHT

DIAMETER Mode

Display shows DIAMETER when the trigger is released

LCDHUD

HEIGHT / DIAMETER ModeEnter the horizontal distance from the instrument to the face-of-the-tree at the point where the diameter is to be measured or shoot to that point with an Impulse laser and it will automatically load that value.

Aim at the base of the tree, press and release the trigger – the display will show degrees to the base of the tree.

Enter a diameter that needs to be located (example: 80% of DBH on a 13-inch tree the target diameter is 10.4 inches) Enter 10.4 and press ENTER.

Press the trigger, which activates the inclination sensor and begins displaying on the HUD and LCD the heights. Releasing the trigger freezes the height sensor and measurement bar. Press and hold the trigger to scan to a different location. Repeat until the tree is exactly bracketed by the measurement bar.

HEIGHT / DIAMETER Mode

Significance of Horizontal

Distance Errors

Errors in diameter measurements will vary with distance from the tree, height on the tree where the diameter is being measured and the size of the diameter.

A 10-inch diameter being measured from 50 feet out from the tree and 50 feet up the tree will result in approximately 0.1-inch error in diameter for each foot of error in distance from the tree.

2 Considerations for

HORIZONTAL DISTANCE

1. For Determining Tree DIAMETER

Measure HD to the face of the tree.

2. For determining tree height for VOLUME

Measure HD to the central axis under the top of the tree.

Measuring Horizontal Distance to Attain Tree Diameter

HD

Solution for Measuring Distances to

Obscured Sections of a Tree or Leaning Trees

With an Impulse laser connected to the dendrometer measure the distance two or more clearly visible points on the tree. The slope distance to the point where the diameter measurement is needed can then be calculated based on the inclination to that point.

Or, if there is foliage obscuring the view to the tree toggle to the Gate Window menu and set the short gate distance to the approximate horizontal distance to the tree being measured.

Now the laser instrument will ignore the intervening foliage.

Measuring Horizontal Distance to Attain Tree Height for Volume Determination

HD

Impulse 200 - Standard

Dimensions: 6 x 2.5 x 5 inches

Weight: 2.2 pounds

Range Accuracy: +0.1 feet

Maximum Range: to a tree 450 feet or to a reflector 750 feet

Rugged, waterproof construction

Tree height measurements in seconds! Tree

Height

Consequences of Distance

Error to Tree HeightIf the cruiser is an equal distance from the tree as the tree is tall (45 degrees viewing angle to the top), for every 1% error in distance from the tree there is a 1% error in height.If nearer the tree there is more than 1% error in height for each 1% error in distance.

SignificanceTree height is used for volume, value and growth & yield determination.Volume (cf) of immature Douglas fir in British Columbia:

log V = 2.85805 + 1.739925 log D + 1.133187 log HSo calling a 20" DBH tree that's 120 ft. tall (5% error in height) results in a 5.5% error in volume.

Proper technique for

measuring tree heightsMeasure heights from a distance at least equal to the height of the tree, with the horizontal distance measured to a point located directly under the top of the tree andCorrect the length based on the measured height and the displacement of the top from the base.

Height error when lean is

towards the cruiser

Tree Height = 100 feet

Degree of lean Distance from base of tree50 feet 100 feet

1 degree 3.6% 1.8% 2 degrees 7.5% 3.6% 5 degrees 33.3% 9.5%

10 degrees 53.2% 21.0% 15 degrees 107.3% 34.9%

Height error when lean is

away from the cruiserTree Height = 100 feet

Degree of lean Distance from the base of tree50 feet 100 feet

1 degree -3.4% -1.7% 2 degrees -6.5% -3.4% 5 degrees - 14.8% - 8.0%

10 degrees - 25.8% - 14.8% 15 degrees -34.1% -20.6%

HD

The most accurate method to measure tree heights is with a laser instrument.

First, determine the horizontal distance (HD) to the central axis of the tree under the top.

Vertical Distance to BASE

Then shoot the angle to the base of the tree to determine the vertical distance from the horizontal to the base of the tree.

Vertical Distance to

TOP

Then shoot the angle to the top of the tree to determine the vertical distance from the horizontal to the top of the tree.

HEIGHT

The next push of the firing button solves for tree height.

Height

The Next Best Procedure

Place a reflector directly under the top of the tree, at the parallel to the base.

With the electronic filter turned ON, scan back and forth until the laser locks onto the reflector, fire the laser again to get the base angle and then shoot the angle to the top of the tree.

Happy Cruising !

MONTANA