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Laser technology used in forest inventory

Columnist Jim Hilton explores the use of light detection and ranging in forestry.

Most people are familiar with the use of radar for detection of airplanes or on ships for detection of hazards but for forest inventory a new system called LiDAR (Light Detection and Ranging) or ALS (Airborne Laser Scanning) is relatively new to most foresters, even though it has been around for 25 years.

It appears that it takes time for the technology to develop and for professionals  to accept new concepts.

Forest inventory has traditionally been done using airphotos which were used to stratify the forests into units (polygons) with similar attributes (species, age, heights , volumes, etc.)

This classifying of forests was done using stereo pairs of photos which allowed the user to see the trees and landscape in three dimensions.

Not everyone has the ability  to use stereo airphotos but with practice some people can become very skilled at identifying unique forest stand structures which allow the production of inventory maps needed for the calculation of the annual allowable cut and orderly harvesting practices.

The accuracy of the photo interpretation is improved with field checks and air calls (visual as well as photo aided checks) using helicopters.

The inherent weakness in the photo interpretation approach is the reliance on the subjectivity of the photo interpreters and trying to get consistency between the practitioners.

The ALS equipment (laser ranging unit, scanner control and GPS monitoring devices) are mounted in a fixed wing aircraft or a helicopter for use in more rugged terrain.

The entire area of interest is scanned and provides a detailed objective series of polygons with similar heights, stem densities and tree canopy structures.

A carefully planned field check program allows the study of additional attributes like species and volumes which when combined with the traditional photo inventory information produces a much more objective, accurate and useful product.

While the LiDAR technology  is relatively expensive at this time, some of the users feel it is worth the effort and claim they have covered the extra costs in a couple of years because of the improved accuracy and information that is provided.

Like most new technologies  the instruments improve and the costs usually decrease as they are used by more people.

Some governments like Alberta have seen the benefits and invested in developing the first stage of the process of deploying it over a large portion of the landscape which can then be used by a variety of natural resource users.

Some BC companies have used it on their private lands and area based tenures. Ontario also seems to be using the new technology and many of their forests.

Ken Day and staff at the UBC Research Forest have used the technology on the lands they manage and are providing an introductory training session on the results of their work.

A local forest company has also used the technology on their tree farm licences and no doubt some of the community forests will be interested as well.

Jim Hilton is a professional agrologist and forester who has lived and worked in the Cariboo Chilcotin for the past 40 years. Now retired, Hilton still volunteers his skills with local community forests organizations.