Forest Management Tech Tips Logo of USDA Technology & Development Program
February 1998
2400 9824 1307–SDTDC



RANGEFINDER COMPARISON

Lois P. Sicking, Mechanical Engineer

INTRODUCTION
Rangefinders are used to measure distance in a variety of applications for various resource needs in the U.S. Department of Agriculture (USDA) Forest Service. Many different types of rangefinders are commercially available and there have been recent advances in rangefinder technology.

The cost of rangefinders varies from $60 to $12,000. Performance varies as much as cost. Significant factors in evaluating performance are range, accuracy, ease of use under field conditions, size, and weight.

The required accuracy varies accroding to the application or the task being performed. Typical applications include determining the distance to surrounding trees from a plot center, determining the distances from one fixed point to another as in traversing, and calculating tree heights. In addition, rangefinders can be used to help determine the volume of a specific tree or stands of timber. The current trend, in the USDA Forest Service and other agencies, is to use more tree measurement sales with lump sum payments. Consequently, it is imperative that the volumes stated in the contracts be very accurate.

Some rangefinders are very accurate, lightweight, and compact. Others are heavy and cumbersome. The size and weight of equipment carried in the field vest is a consideration for applications which entail walking long distances or on steep terrain.

OBJECTIVE
This test was designed to evaluate the performance of various rangefinder devices. The range, accuracy, size, and weight of these devices were compared. Test workers were surveyed for their opinion regarding ease of use. Comments were solicited on what effect the weather or other field conditions appeared to have on the readings. Additional performance features were noted. The project goal was to provide information to the field on the performance of various laser, ultrasonic and other current rangefinder devices. There is potential for considerable cost savings for field personnel using this information when selecting the appropriate rangefinder for the application.

RANGEFINDER TECHNOLOGIES

Ultrasonic
Ultrasonic distance-measuring devices use a wide band frequency from a transducer, sending out narrow beams of sound waves which “bounce” off an object. The return signal is picked up by a hand- held receiver. Accuracy is effected by the position of the receiver, outside sound waves, and noise. Noise generated by wind through the trees or brush, streams, rain, crew conversations, road traffic, or birds chirping can effect readings. When a horizontal distance measurement is being taken, the inclination or horizontal position of the receiver is critical. An outgoing wide band signal will be scattered, increasing the error, if the transducer is not positioned as close to horizontal as possible.


Optical
Optical distance-measuring devices typically use the coincidence method of determining distance; which uses a series of lenses and mirrors to produce a double image. The double images on mirrors are brought together by rotating a dial until both images merge into one. The dial has a distance indicator. When the two images merge, the distance to the target is read directly off the dial.


Laser
Pulse lasers determine distance by measuring the amount of time required for a pulse of infrared light to travel to the target and back. The speed of light is constant, so this amount of time is directly proportional to the distance. Many pulses are sent out and returned for each shot, improving the accuracy of the calculated value. Laser instruments are narrow band and require the operator to aim with some accuracy. The accuracy and maximum range of some laser instruments are dependent on the reflectivity of the target. Some laser instruments are affected by the power level of the batteries.

RANGEFINDER SELECTION CRITERIA
The rangefinders selected for testing were identified as representing the majority of commercially available rangefinders. In addition, rangefinder test devices were screened as meeting specific minimum criteria, appropriate for current typical applications. The minimum criteria for this test included size, weight, cost below $4,000, and no need for the placement of reflective target in order to obtain a measurement. The test devices were assembled and calibrated in accordance with manufacturers' recommendations.

INSTRUMENT DESCRIPTIONS
All ranges listed within the following product descriptions are manufacturer-rated ranges.


Sonin 60 (figure 1)

  • Operates as an ultrasonic device with a range of 1 to 60 feet
  • Measures units as small as 1 inch
  • Computes areas and volumes; adds and subtracts same
  • Equipped with a walking measurement mode and limited data storage
  • Capable of converting measurements from feet to inches, meters to centimeters, and deca feet to yards
  • Equipped with a carrying case
  • Requires a 9-volt battery
  • Equipped with an automatic shutoff
Figure 1—Sonin 60 rangefinder.
Figure 1—Sonin 60 rangefinder.


Power Disto (figure 2)
  • Operates as a laser device with a range of 1 to 90 feet, without use of reflective target and 1 to 300 feet with a target
  • Measures units as small as 0.001 feet.
  • Computes areas and volumes; adds and subtracts same
  • Provides for data storage and retrieval
  • Capable of converting feet to meters
  • Equipped with a carrying case
  • Requires specific NiCad batteries
  • Equipped with a low-battery indicator and an automatic shutoff
  • Includes battery charger with adapter to charge off car battery
  • Designed to be rainproof to IP 52 and IEC 529
  • Approximately 400 measurements can be taken per charge, with a charging time of 1 hour
Figure 2—Power Disto rangefinder.
Figure 2—Power Disto rangefinder.


DME 70 (figure 3)
  • A laser device with a range of 10 to 225 feet
  • Measures units as small as 1 yard
  • Capable of converting measurements from yards to meters
  • Equipped with a carrying case
  • Requires a 9-volt battery
  • Equipped with a low-battery indicator and an automatic shutoff
  • Equipped with light and audio indicators for locking onto target
Figure 3—DME 70 rangefinder.
Figure 3—DME 70 rangefinder.


Lytespeed 400 (figure 4)
  • Operates for a range of 400 yards without the use of a reflective target, and up to 999 yards with a target
  • Measures units as small as 1 yard (0.9 m)
  • Capable of converting measurements from yards to meters
  • Equipped with a carrying case and straps
  • Requires a 9-volt battery
  • Equipped with a low-battery indicator and an automatic shutoff
  • Designed to be water and shock resistant
  • Operates as a laser-infrared device with amonocular to assist in target location
  • Designed with a target-quality gauge to scan targets that may be difficult to lock onto and to find the most reflective point
  • Designed with a Rain Mode feqture that allows measurements to be taken in light pricipitation with a range of 65 to 400 yards
  • Equipped with a Brush Mode filter that allows targeting an object through light brush in a range of 115 to 400 yards
Figure 4—Lytespeed 400 rangefinder.
Figure 4—Lytespeed 400 rangefinder.


Impulse 200 (figure 5)
  • Operates as a laser device with a range of up to 1,640 feet with the use of a reflective target
  • Measures units as small as 0.01 feet
  • Calculates height, horizontal, vertical, and slope distances, cumulative and difference distances, and inclination.
  • Equipped with data storage and retrieval via serial interface using an RS-232 port, accessed with a LEMO 4-pin to DB 9-pin cable or LEMO 4-pin to HP 200/48 10-pin cable.
  • Designed to run available data collection software including LTI Map, LTI Face Profiler, and Traverse Handheld
  • Interfaces available for GPS mapping systems include Ashtech Reliance, Trimble Pathfinder, and CMT MC-PS
  • Capable of converting measurements from feet to meters and degrees to grads to percent slope
  • Equipped with carrying case, hand strap, and belt clip
  • Requires two AA batteries for a power supply of up to 20 hours of continuous use
  • Equipped with low-battery and battery-voltage indicators, with multiple error condition indicators
  • Equipped with an automatic shutoff
  • Designed to operate with optional mechanical compass and mount, monopod, tripod yoke, and mount
  • Equipped with a filter mode for shooting through foliage
  • Waterproof to IP 67 and NEMA 6
  • Allows for aligning and calibrating the tilt sensor and realigning the scope by user
  • Converts easily for left- or right-handed use
Figure 5—Impulse 200 rangefinder.
Figure 5—Impulse 200 rangefinder.


Laser Atlanta Advantage (figure 6)
  • Operates as a laser device with a range of 5 to 32,000 feet with the use of a reflective target.
  • Measures units as small as 0.1 feet
  • Calculates the missing line distance, incscribed, right triangular, and rectangular areas based on two or more points
  • Capable of data storage and retrieval via configurable RS-232 port and via PCMCIA Type II SRAM Cards
  • Designed to be compatible with GPS, Pen Computer, and Data Logger software
  • Capable of converting measurements from feet to meters
  • Equipped with a water resistant carrying case
  • Requires 6-volt NiCad batteries
  • Equipped with an additional battery pack
  • Designed for each battery pack to provide power for 5 hours of continuous use
  • Requires a charging time of 10 to 12 hours
  • Equipped with a low battery indicator and an automatic shutoff
  • Includes a battery charger and adapter to charge off car battery
  • Contains an integrated digital compass/inclinometer in the C/I version
  • Equipped with a compass that is a strapped-down magnetometer
  • Designed for optional 8X monoscope for distant viewing, monopod and tripod for mounting
Figure 6—Laser Atlanta Advantage rangefinder.
Figure 6—Laser Atlanta Advantage rangefinder.


Swarovski Optik RF-1 (figure 7)
  • Operates as a laser device with a range of 22 to 1,100 yards without the use of a reflective target
  • Measures units as small as 1 yard
  • Equipped with a protective lens cap and carrying case
  • Requires six AA batteries
  • Designed for each battery pack to last up to 2,000 measurements
  • Equipped with a low-battery indicator
  • Equipped with a 6X monocular viewer, with an integrated 6- by 24-inch telescope with focusing capabilities
Figure 7—Swarovski Optik RF-1 rangefinder.
Figure 7—Swarovski Optik RF-1 rangefinder.


Ranging 400 (figure 8)
  • Operates as an optical device which uses the coincidence method of determining distance, with a range of 20 to 400 yards
  • Measures smallest units from 0.5 to 1 yard on a dial indicator
  • Available with optional carrying case
  • Requires no battery
  • Includes a 3X monocular to assist in locating the target
  • Allows for a calibration adjustment image adjustment by the user
Figure 8—Ranging 400 rangefinder.
Figure 8—Ranging 400 rangefinder.

RANGEFINDER TESTING
Testing was conducted on the Mount Baldy Ranger District of the Angeles National Forest. The same target was used for all devices, so the measurements could be compared with statistical validity. Flagging was placed on the target at diameter breast height of 4 feet 8 inches.

An Electronic Distance Measuring (EDM) infrared rangefinder was designated as the reference device used to measure the true distance (i.e., standard measurement). A professional land surveyor team used the EDM to measure all data points from the target, forward and backward. The range of distance was 500 feet. All devices were tested at 10-foot increments, up to 100 feet, then continuing at 25- foot increments up to 110 percent of the maximum manufacturer's rated range, or 500 feet, whichever was greater.

Three operators were selected to participate in testing, all of similar height. Two operators were experienced in taking slope distance measurements.

STATISTICAL METHODS AND RESULTS
Accuracy denotes the absolute nearness to the truth. In contrast, precision denotes degree of repeatability in the taking of a measurement. The range of percent differences is an indicator of precision. The data reduction results are presented in table 1.


Percent Inaccuracy
The percent inaccuracy is the inaccuracy specification that could be met at the 95 percent confidence level. Assumptions are made that the data here was not a 1-in-20 or rarer anomaly and that the test measurements follow a normal distribution with the mean equal to the standard measurement. From these results, the smallest inaccuracy standard is met by the Laser Atlanta Advantage, followed closely by the Impulse 200.


Percent Bias
Percent bias indicates whether the tool consistently over- or under- measures values. Bias can be used as a correction factor for measured values to obtain the true value. This correction factor is specific for each tool and may vary across the range of measured values. The percent bias values in table 1 were averaged across the range of values. From these results, the smallest bias standard is met by the Laser Atlanta Advantage, followed closely by the Impulse 200.


Percent Differences
Percent differences were calculated between the standard measurement and the test device measurement. The smaller the range of percent difference, the better. The smallest range of percent differences is met by the Impulse 200, followed closely by the Laser Atlanta Advantage.
Table 1—Rangefinder Data Reduction Results.
  Sonin 60 Power Disto DME 70 Lytespeed 400 Impulse 200 Laser Atlanta Advtg. Swarovski Optik RF-1 Ranging 400

Percent Inaccuracy
Operator 1 11.62 0.36 4.32 1.43 0.35 0.21 1.22 3.28
Operator 2 9.76 1.36 4.55 1.47 0.43 0.20 1.15 3.65
Operator 3 11.11 0.73 3.01 1.51 0.31 0.19 1.40 4.59
All Operators 10.83 0.82 4.00 1.47 0.36 0.20 1.26 3.74
Percent Bias
Operator 1 -11.59 0.12 -4.16 1.11 -0.32 -0.06 -1.15 3.58
Operator 2 -11.11 1.35 -4.48 1.13 -0.42 0.01 -1.00 -3.93
Operator 3 -11.11 1.17 -2.72 1.21 -0.26 -0.01 -1.14 -5.80
All Operators -11.30 0.88 -3.79 1.15 -0.34 -0.02 -1.14 -2.16
Range of Percent Differences for all Operators
Minimum -13.0 -0.63 -8.9 -1.03 -0.95 -0.88 -3.79 -40
Maximum -7.7 1.67 -1.0 5.98 0.30 0.94 0.68 13
Total Range 5.3 2.30 7.9 7.01 1.25 1.82 4.47 53

DISCUSSION
Percent differences were calculated between the standard measurement and the test device measurement. The smaller the range of percent difference, the better. The smallest range of percent differences is met by the Impulse 200, followed closely by the Laser Atlanta Advantage.

There was minimal difference in measured values, percent inaccuracy, percent bias, and percent differences between inexperienced and experienced operators.

The same target, a market section of bark, was used for all operators. No reflective targets were used in the testing. Surface finish, color, size, and shape of the bark affect reflectivity and range. All readings were taken at the same height and on the same tree surface. No optional monoscopes for distant viewing were used, only built-in monoscopes. No monopods or tripods were used for mounting. Test conditions were the same for all operators.

As recommended by laser rangefinder manufacturers, all testing was conducted with fresh batteries for each operator in order to avoid varying performance caused by battery decays. Operators noted that rangefinders are much easier to carry through the workday with the use of a neck strap or shoulder yoke. Some rangefinders provided neither. Both neck straps and shoulder yokes are readily available commercially and easily adaptable to the rangefinders used in this study.

User manuals were supplied with all rangefinders and were available to all operators before testing. Brief verbal instructions were also given to all operators.

An attempt was made to shoot through light, medium, and dense foliage with the test rangefinders. Only the rangefinders with a filter were able to shoot through brush and only on a limited basis.

In addition to accuracy testing, each operator was asked to subjectively rate the instruments on a scale of 1 to 8, with 1 being the most favorable. The ratings are as indicated in table 2.

Table 2—Operator Rating of Test Instruments.
  Targets Ease to Locate Ease of Use Readings Dependable Easy to Learn Better than Log Tape or Survey Chain Overall Rank

Sonin 60 8 5 8 7 7 7
Power Disto 6 1 6 5 6 6
DME 70 5 3 5 1 5 5
Lytespeed 400 2 5 3 3 2 4
Impulse 200 3 3 1 5 1 1
Laser Atlanta Advtg 4 2 1 4 2 1
Swarovski Optik RF-1 1 5 4 2 2 3
Ranging 400 7 8 7 8 7 8
Test operators were asked for comments regarding the rangefinders immediately after testing was completed. Their comments are as indicated in table 3.


Table 3—Comments on Rangefinder Test Units by Operators Immediately After Testing.
Rangefinder Pros Cons
Sonin 60 Fits easily into cruiser vest pocket.
Inexpensive
Measures for short distance only. Must shoot
absolutely level to tree to get good reading.
Power Disto Fits into cruiser vest back pocket. Measures for short distance only.Must shoot
absolutely level to tree. Not appropriate for outdoor
use. Expensive.
DME 70 Very small. Shoots quickly. Audio
signal helpful. Inexpensive
Not weatherproof. No plastic case. Measures in yards
and meters only. Does not magnify target. Hard to use
with gloves on.
Lytespeed 400 Magnifies target. Reading inside the
viewer. Neck strap. Soft rubber eye-
piece for comfort and is removable if
wearing glasses. Inexpensive.
Measures in yards and meters only. Hard to push
button with gloves on.
Impulse 200 Easy aim. Quick shot. Left- or right-
handed use. Hand strap.
Confusing to operate. Does not look weatherproof.
More options and more complicated. For its weight, it
should have a neck strap for easy transport. Does
not magnify, so target is hard to see at far distances.
Laser Atlanta Advantage Shoots slope and horizontal distance
quickly. Switches easily between feet/
yards/meters. Has data card; data re-
corder adapter; rechargeable battery
in the handle; backup battery
Very heavy and bulky. Not something I would like to
hike around with for a long distance. Reading given
the viewer is less accurate (1 foot) than the
reading on the instrument face (0.1 foot).
To manually record readings, operator must look up onto
instrument face.
Swarovski Optik RF-1 Magnifies target. Easy operation. One
button only. Reading inside the viewer.
Neck strap. Fits easily into cruiser
vest pocket.
Measures in 2-yard increments and have to find
where values change between even yards to determine
the 1 yard (0.9 m)measurement. Feels topheavy.
Expensive.
Ranging 400 No batteries. Inexpensive. Hard to focus. Takes longer to use. Hard plastic eyepiece.
Small eyepiece. Difficult to operate.

Table 4 provides a comparison by range, price, weight, and size.

Table 4—Comparison of Range, Price, Weight, and Size of Test Instruments.
  Range capability
noted in testing
(Feet)
(m)
Price

($)
Weight
incl. batteries
(Pounds)
(Kg)
Size

(Inch)
(mm)
Sonin 60 5 to 15
(1.5 to 4.6)
70 0.4
(0.2)
5.6 by 2.7 by 1
(142 by 69 by 25)
Power Disto 10 to 60
(3 to 18)
1,795 1.8
(0.8)
9.3 by 4 by 2.2
(236 by 102 by 56)
DME 70 10 to 250
(3 to 76)
290 0.6
(0.3)
5 by 1.75 by 4
(127 by 45 by 102)
Lytespeed 400 60 to 500*
(18 to 152)
260 1.0
(0.5)
6 by 2.5 by 5
(152 by 64 by 127)
Impulse 200 10 to 500*
(3 to 152)
2,900 2.2
(1.0)
6 by 2.5 by 5
(152 by 64 by 127)
Laser Atlanta Advantage 10 to 500*
(3 to 152)
3,000 4.4
(2.0)
10 by 3 by 11
(254 by 76 by 279)
Swarovski Optik RF-1 60 to 500*
(18 to 152)
3,300 2.4
(1.1)
5.9 by 4.7 by 2.4
(150 by 119 by 61)
Ranging 400 60 to 500*
(18 to 152)
70 1.3
(0.6)
10.5 by 2 by 4
(267 by 51 by 102)
Note* = Rangefinder was measured to the maximum test range. Distance/accuracy beyond the maximum test
range, up to the maximum manufacturer range was not tested. See Instrument Descriptions.

CONCLUSION
This report includes information on rangefinder descriptions, percent inaccuracy, percent bias, user comments, user rankings, cost, weight, and size. The user in the field has an indepth knowledge of what is required to get the job done. Consequently, with this knowledge base and the results of this comparison study, the user is equipped to determine the best instrument for the job.

MANUFACTURERS
DME 70
DME Golf
3180 Red Hill Avenue
Costa Mesa, CA 92626
714–432–7100

Impulse 200
Laser Technology Incorporated
7070 South Tucson Way
Englewood, CO 80112
303–649–9710

Laser Atlanta Advantage
Laser Atlanta Optics, Incorporated
2827 Peterson Place
Norcross, GA 30071
770–446–3866

Lytespeed 400
Bushnell Sports Optics Worldwide
9200 Cody
Overland Park, KS 66214-3259
913–752–3400

Power Disto
Leica Incorporated
BAC Department
3155 Medlock Bridge Road
Norcross, GA 30071
800–367–9453

Ranging 400
Ranging Company
Routes 5 & 20
East Bloomfield, NY 14443
716–657–6161

Sonin 60
Sonin Incorporated
670 White Plains Road
Scarsdale, NY 10583
914–725–0202

Swarovski Optik RF-1
Swarovski Optik
4023 City View
San Antonio, TX 78228
800–635–3890

ACKNOWLEDGMENTS
This report is the result of the efforts of many USDA Forest Service employees, with a special thanks to:

Jim Landrum
Measurement Specialist
Angeles National Forest

Cliff Johnson
Professional Land Surveyor
Realty Specialist
Angeles National Forest

Hal Seyden
Vegetation Management Team Leader
San Bernardino National Forest

Thomas Threlkeld (retired)
Measurement Specialist
Region 1

Brian Wagner
Measurement Specialist
Region 1

Ben Lowman
Program Leader
Missoula Technology and Development Center

Bill Carr
Member, Board of Directors
Laser Technology Incorporated


TD logo
For Additional Information Contact:
Forest Management Program Leader
San Dimas Technology and Development Center
444 East Bonita Avenue, San Dimas CA 91773-3198
Phone 909-599-1267; TDD: 909-599-2357; FAX: 909-592-2309
E-mail: mailroom_wo_sdtdc@fs.fed.us

Information contained in this document has been developed for the guidance of employees of the Forest Service, United States Department of Agriculture (USDA), its contractors, and cooperating Federal and State agencies. The USDA assumes no responsibility for the interpretation or use of this information by other than its own employees. The use of trade, firm, or corporation names is for the information and convenience of the reader. Such use does not constitute an official evaluation, conclusion, recommendation, endorsement, or approval of any product or service to the exclusion of others that may be suitable.

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