LIDAR-QUEBEC-BOREAL
ENGLISH
Here's a summary of the thesis:
Forest
covers 40 % of terrestrial areas and Canada holds 10 % of it
alone, mostly in a boreal setting. The need for planning and
supervising implied by this reality couldn't be filled entirely
by traditional means (forest inventories), especially for wood
volume, an essential measurement for ecology researchers and
forest engineers. A technology named "laser altimetry",
which has been in development for several years, seems promising
in that regard. It is based on geometric properties: the reflection
of a laser beam by any object intercepted. The time elapsed
between emission and reception gives the distance between the
instrument and the object and, by way of calculation, the
elevation of surfaces. Combining a high-resolution scanning laser
with a higher sampling intensity, a precise positioning by INS-GPS
and an adequate volume model should resolve any remaining
shortcomings of that technology so far.
The experimental method was applied mostly on stands which
contained two species, a deciduous tree (Populus
tremuloides Michx.) and a coniferous one (Picea
glauca [Moench] Voss), both abundant in the
Conservation Zone of "Forêt d'Enseignement et de Recherche
du Lac Duparquet" (FERLD), in Abitibi, Québec. Volume derived
from a sample inventory (38 square plots of 400 m2) done in
the summer of 1999 were compared with calculations obtained from
the data of an airborne LIDAR (Optech ALTM1020), taken from three
flights in the summer of 1998 (400 000 ground points and two
million vegetation points). Many of the one-variable relationships
tried out proved significant in explaining the ground-truth
volume (r2 = 0,52 to 0,77); but the statistical tests linking
each of the 8 laser pseudo-volumes to ground wood volumes by a
quadratic model gave better results, especially in the case of a laser
interpolation were values less than the mean height were left out.
Combining that calculation with the cover ratio gives even better
results, at least for aspen (r2 = 0,88, good up to 50 m3/ha of
variation). If small volumes would have been taken into account (less
than 200 m3/ha), results would have been even better still. With
the help of stratified classes (density, height and species
groupings), a practical cartography of the study zone could be
achieved (digital terrain models and vegetation surface models).
You might also be interested in taking a look at the section of the site named "Cartes" (Maps).
Keywords: altimetry, laser, LIDAR, height, volume, forest, FERLD,
Duparquet, Abitibi
Conception: Alain Renaud, août 2000