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M. Hollaus, W. Dorigo, W. Wagner, K. Schadauer, B. Höfle, B. Maier:
"Operational wide-area stem volume estimation based on airborne laser scanning and national forest inventory data";
International Journal of Remote Sensing, 30 (2009), 19; 5159 - 5175.

This paper evaluates the performance of a recently developed approach for widearea
stem volume estimations based on airborne laser scanning (ALS) and national
forest inventory (NFI) data in the case where data recorded under operational
conditions are used as input. This entails that neither ALS data nor NFI samples
were collected and optimized for the current study. The approach was tested for the
Austrian state of Vorarlberg, which covers an area of 2601 km2 and encloses about
970 km2 of forest land.ALS data with point densities varying between 1 and 4 points
m-2 were acquired in the framework of a commercial state-wide terrain mapping
project during several winter- and summer-flight campaigns. The stem volume
model was calibrated with allNFI data available for Vorarlberg, whereas additional
local forest inventory data were used for independent validation.Moreover, several
relevant operational issueswere addressed in this study, such as the determination of
the optimum area used to calculate the reference laser metrics input to themodel, the
effect of gridding point cloud data to speed up processing, and the stratification of
input data into coniferous and deciduous sample plots.
Without tree species stratification and based on the 3D laser heights model,
calibration provided a maximum R2 of 0.79 and a standard deviation (SD) of
residuals derived from cross-validation of 107.4 m3 ha-1 (31.5%). Calibrating the
model only with coniferous samples increased the achieved R2 to 0.81 and
decreased SD to 104.8 m3 ha-1 (29.7%). As only eight NFI sample plots were
available for deciduous forest a robust calibration of a separate model could not
be obtained. Calibrating the model with a rasterized canopy height model (CHM)
instead of using the 3D laser heights just led to a slight decrease in accuracy
(R2 = 0.75, SD = 120.9 m3 ha-1 (35.5%) without forest-type stratification and
R2 = 0.78 and SD = 117.2 m3 ha-1 (33.1%) for the coniferous stem volume
model). Finally, the stem volume model calibrated with CHM data was adopted
to generate a stem volume map of the entire State of Vorarlberg. Validation of this
map with the additional local forest inventory data confirmed the accuracies
(R2 = 0.75; SD = 135.6 m3 ha-1 (32.3%)) that were derived during calibration
of the stem volume model based on the NFI data. The models and methods
presented in this study are used operationally for forest and environment policy
purposes and practical applications in Austria.

http://dx.doi.org/10.1080/01431160903022894