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Airborne Laser Scanning of Forest Stem Volume in a Mountainous Environment

View Article: PubMed Central

ABSTRACT

Airborne laser scanning (ALS) is an active remote sensing technique that uses the time-of-flight measurement principle to capture the three-dimensional structure of the earth's surface with pulsed lasers that transmit nanosecond-long laser pulses with a high pulse repetition frequency. Over forested areas most of the laser pulses are reflected by the leaves and branches of the trees, but a certain fraction of the laser pulses reaches the forest floor through small gaps in the canopy. Thus it is possible to reconstruct both the three-dimensional structure of the forest canopy and the terrain surface. For the retrieval of quantitative forest parameters such as stem volume or biomass it is necessary to use models that combine ALS with inventory data. One approach is to use multiplicative regression models that are trained with local inventory data. This method has been widely applied over boreal forest regions, but so far little experience exists with applying this method for mapping alpine forest. In this study the transferability of this approach to a 128 km2 large mountainous region in Vorarlberg, Austria, was evaluated. For the calibration of the model, inventory data as operationally collected by Austrian foresters were used. Despite these inventory data are based on variable sample plot sizes, they could be used for mapping stem volume for the entire alpine study area. The coefficient of determination R2 was 0.85 and the root mean square error (RMSE) 90.9 m3ha−1 (relative error of 21.4%) which is comparable to results of ALS studies conducted over topographically less complex environments. Due to the increasing availability, ALS data could become an operational part of Austrian's forest inventories.

No MeSH data available.


Related in: MedlinePlus

The location of the study area Montafon in the western part of the Austrian Alps. The left image shows the flight paths for the airborne laser scanner acquisition during the summer and the winter campaign, overlain over the shaded terrain model. The right image shows the location of the forest inventory plots overlain over the shaded terrain model with highlighted forested areas.
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f1-sensors-07-01559: The location of the study area Montafon in the western part of the Austrian Alps. The left image shows the flight paths for the airborne laser scanner acquisition during the summer and the winter campaign, overlain over the shaded terrain model. The right image shows the location of the forest inventory plots overlain over the shaded terrain model with highlighted forested areas.

Mentions: The study area is situated in the southern part of the federal state of Vorarlberg, Austria (Figure 1) and covers 128 km2 of the Montafon region. The complex alpine landscape of the study area has high relief energy, whereas the elevations range between 800 and 2,900 m. The land cover is characterized by coniferous and mixed forests, shrubs, meadows, and sparsely settled areas in the valley floors. According to the Stand Montafon Forstfonds1 the main tree species in the area are spruce (Picea abies) with 96% and fir (Abies alba) with 3%. Especially in valleys and sunny slopes, mixed forests with the species red beech (Fagus sylvatica) can be found. The mean stem volume of the Montafon region is 465 m3ha−1, which is high compared to 325 m3ha−1 2 representing the average Austrian stem volume. Two thirds of the forests are located above 1,000 m sea level, whereas the timberline is at about 1,950 m. As a result of the mountainous terrain 6% of the forests grow on a slope inclination of more than 45°, and 61% between 30° and 45°. Furthermore, 28% of the forests grow on slopes between 15° and 30°, and only 5% on slopes less than 15°. Approximately 80% of the forested area is managed forest with a protection function (protection forest with yield), 10% is managed forest (commercial forest), and the rest is unmanaged protection forest (protection forest without yield) on extreme sites or at the timberline. In alpine regions protection forests are of great importance to protect inhabited areas, roads and railway lines from natural hazards such as rockfalls and snow avalanches. About half of the forests in the study area are managed by the forest administration Stand Montafon Forstfonds, which is the largest forest owner in Vorarlberg. They operate a precise forest inventory, which provides the field data used in this study. The forested areas managed by the Stand Montafon Forstfonds are regularly distributed over the entire test site and therefore, this forest inventory data are representative for the entire study area. Within the study area the average forest stand size is approximately 3.5 ha and is equal to the average area of private owned forests in Austria.


Airborne Laser Scanning of Forest Stem Volume in a Mountainous Environment
The location of the study area Montafon in the western part of the Austrian Alps. The left image shows the flight paths for the airborne laser scanner acquisition during the summer and the winter campaign, overlain over the shaded terrain model. The right image shows the location of the forest inventory plots overlain over the shaded terrain model with highlighted forested areas.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3814869&req=5

f1-sensors-07-01559: The location of the study area Montafon in the western part of the Austrian Alps. The left image shows the flight paths for the airborne laser scanner acquisition during the summer and the winter campaign, overlain over the shaded terrain model. The right image shows the location of the forest inventory plots overlain over the shaded terrain model with highlighted forested areas.
Mentions: The study area is situated in the southern part of the federal state of Vorarlberg, Austria (Figure 1) and covers 128 km2 of the Montafon region. The complex alpine landscape of the study area has high relief energy, whereas the elevations range between 800 and 2,900 m. The land cover is characterized by coniferous and mixed forests, shrubs, meadows, and sparsely settled areas in the valley floors. According to the Stand Montafon Forstfonds1 the main tree species in the area are spruce (Picea abies) with 96% and fir (Abies alba) with 3%. Especially in valleys and sunny slopes, mixed forests with the species red beech (Fagus sylvatica) can be found. The mean stem volume of the Montafon region is 465 m3ha−1, which is high compared to 325 m3ha−1 2 representing the average Austrian stem volume. Two thirds of the forests are located above 1,000 m sea level, whereas the timberline is at about 1,950 m. As a result of the mountainous terrain 6% of the forests grow on a slope inclination of more than 45°, and 61% between 30° and 45°. Furthermore, 28% of the forests grow on slopes between 15° and 30°, and only 5% on slopes less than 15°. Approximately 80% of the forested area is managed forest with a protection function (protection forest with yield), 10% is managed forest (commercial forest), and the rest is unmanaged protection forest (protection forest without yield) on extreme sites or at the timberline. In alpine regions protection forests are of great importance to protect inhabited areas, roads and railway lines from natural hazards such as rockfalls and snow avalanches. About half of the forests in the study area are managed by the forest administration Stand Montafon Forstfonds, which is the largest forest owner in Vorarlberg. They operate a precise forest inventory, which provides the field data used in this study. The forested areas managed by the Stand Montafon Forstfonds are regularly distributed over the entire test site and therefore, this forest inventory data are representative for the entire study area. Within the study area the average forest stand size is approximately 3.5 ha and is equal to the average area of private owned forests in Austria.

View Article: PubMed Central

ABSTRACT

Airborne laser scanning (ALS) is an active remote sensing technique that uses the time-of-flight measurement principle to capture the three-dimensional structure of the earth's surface with pulsed lasers that transmit nanosecond-long laser pulses with a high pulse repetition frequency. Over forested areas most of the laser pulses are reflected by the leaves and branches of the trees, but a certain fraction of the laser pulses reaches the forest floor through small gaps in the canopy. Thus it is possible to reconstruct both the three-dimensional structure of the forest canopy and the terrain surface. For the retrieval of quantitative forest parameters such as stem volume or biomass it is necessary to use models that combine ALS with inventory data. One approach is to use multiplicative regression models that are trained with local inventory data. This method has been widely applied over boreal forest regions, but so far little experience exists with applying this method for mapping alpine forest. In this study the transferability of this approach to a 128 km2 large mountainous region in Vorarlberg, Austria, was evaluated. For the calibration of the model, inventory data as operationally collected by Austrian foresters were used. Despite these inventory data are based on variable sample plot sizes, they could be used for mapping stem volume for the entire alpine study area. The coefficient of determination R2 was 0.85 and the root mean square error (RMSE) 90.9 m3ha−1 (relative error of 21.4%) which is comparable to results of ALS studies conducted over topographically less complex environments. Due to the increasing availability, ALS data could become an operational part of Austrian's forest inventories.

No MeSH data available.


Related in: MedlinePlus