88
4.3.1.1 Measurements of Leaf Optical Properties
To obtain the optical properties of tree foliage, we used an integrating sphere coupled with an Analytical Spectral Devices (ASD) FieldSpec-3. Measurements of
hemispherical and directional reflectance and transmittance, both from the abaxial
and adaxial side of the leaves, were taken. To take into account the vertical variability of LOPs, we sampled in three different crown parts (top, middle, bottom), representing different lighting conditions in the canopy (e.g., sunlit, transitional, shaded).
Deciduous leaves were collected from ten individual trees of five species (Acer
pseudoplatanus spp., Fagus excelsior, F. sylvatica, Ulmus glabra, and Tilia platyphyllos). Measurements of aerosol optical depth (AOD) and precipitable amount of
water (PAW) were provided by the aerosol robotic network (AERONET) as level
2.0 quality-assured data. For details of the sampling and measurement scheme, see
Schneider et al. (2014).
4.3.1.2 Forest Inventory
An exhaustive forest inventory was carried out, individually addressing all single
trees with a diameter at breast height (DBH) above 20 cm on the 300 m × 300 m site.
Variables recorded for each tree included DBH, species, social status, and crown
shift (i.e., an estimation of the magnitude and horizontal direction of the crown
center in respect to the foot of the stem). The latter is of particular relevance on the
Laegeren site because many trees have leaning stems due to topography and shallow
soils. A geodetic tachymeter was used for the surveying, enabling fast and accurate
electronic tree location measurements. Using all measured points, a polygonal traverse was calculated resulting in the x, y, z coordinates for each measurement position with an error range of millimeters for the TLS measurements and a maximum
of 10 cm in x, y, and z for all other field measurements. The relative locations were
transformed to absolute Swiss national coordinates using three differentially corrected global positioning system (GPS) base points, which were placed in canopy
gaps. See Fig. 4.3 for a visualization of the tree inventory.
4.3.2 RS Data
4.3.2.1 Airborne Laser Scanning
To provide 3-D structure information across the whole study area, we relied on two
airborne laser scanning campaigns, using a RIEGL LMS-Q680i scanner under leafon conditions and a RIEGL LMS-Q560 scanner under leaf-off conditions. Flight
strips have an overlap of approximately 50%. Full-waveform features, namely, echo
width and intensity, were extracted from the data using the software RiANALYZE
and were assigned to the individual returns in the multiple-echo point cloud.
F. Morsdorf et al.
4.3.1.1 Measurements of Leaf Optical Properties
To obtain the optical properties of tree foliage, we used an integrating sphere coupled with an Analytical Spectral Devices (ASD) FieldSpec-3. Measurements of
hemispherical and directional reflectance and transmittance, both from the abaxial
and adaxial side of the leaves, were taken. To take into account the vertical variability of LOPs, we sampled in three different crown parts (top, middle, bottom), representing different lighting conditions in the canopy (e.g., sunlit, transitional, shaded).
Deciduous leaves were collected from ten individual trees of five species (Acer
pseudoplatanus spp., Fagus excelsior, F. sylvatica, Ulmus glabra, and Tilia platyphyllos). Measurements of aerosol optical depth (AOD) and precipitable amount of
water (PAW) were provided by the aerosol robotic network (AERONET) as level
2.0 quality-assured data. For details of the sampling and measurement scheme, see
Schneider et al. (2014).
4.3.1.2 Forest Inventory
An exhaustive forest inventory was carried out, individually addressing all single
trees with a diameter at breast height (DBH) above 20 cm on the 300 m × 300 m site.
Variables recorded for each tree included DBH, species, social status, and crown
shift (i.e., an estimation of the magnitude and horizontal direction of the crown
center in respect to the foot of the stem). The latter is of particular relevance on the
Laegeren site because many trees have leaning stems due to topography and shallow
soils. A geodetic tachymeter was used for the surveying, enabling fast and accurate
electronic tree location measurements. Using all measured points, a polygonal traverse was calculated resulting in the x, y, z coordinates for each measurement position with an error range of millimeters for the TLS measurements and a maximum
of 10 cm in x, y, and z for all other field measurements. The relative locations were
transformed to absolute Swiss national coordinates using three differentially corrected global positioning system (GPS) base points, which were placed in canopy
gaps. See Fig. 4.3 for a visualization of the tree inventory.
4.3.2 RS Data
4.3.2.1 Airborne Laser Scanning
To provide 3-D structure information across the whole study area, we relied on two
airborne laser scanning campaigns, using a RIEGL LMS-Q680i scanner under leafon conditions and a RIEGL LMS-Q560 scanner under leaf-off conditions. Flight
strips have an overlap of approximately 50%. Full-waveform features, namely, echo
width and intensity, were extracted from the data using the software RiANALYZE
and were assigned to the individual returns in the multiple-echo point cloud.
F. Morsdorf et al.