Other Tree Insights
Tree Crown Density and Background Noise
Results:
- There was little effect of background noise on tree crown transflectance levels
- Net foliage transflectance level of sparse foliage measured was lower than that of dense foliage
“Sparse foliage degrades tree radiative performance”
Results:
- Maximum tree crown transflectance levels appeared at 1.8 m height nearly without concave shapes in the measuring patch
- The minimum tree crown transflectance levels appeared at 2.5 m height,with concave shapes accounting for approximately half of the area of the viewing vision
- The tree crown transflectance levels at other heights with concave shapes of different extents fell in between
“Concave crown contours decrease tree radiative performance, while vice versa, convex contours maximizes tree radiative performance”
Results:
- Tree crown transflectance increased as solar altitude rises on sunny days
- The correlation could be seen for the other 9 species of trees measured
- However, the results were slightly more inconsistent for Betula pendula and Aesculus hippocastanum trees. It was presumably due to the sparse leaf density of the former species, and the development of horse chestnut leaf-miner during summer for the later species.
“Tree radiative performance increases as solar altitude rises”
Spatial distribution – Horizontal loop
Results:
- Maximum transflectance appeared along the solar azimuth direction
- Minimum transflectance was recorded along the solar azimuth + 180° direction
- Transflectance levels in directions in solar azimuth + 90° and + 270° were similar, when no obvious concave contours could be viewed on both sides.
“Tree crown transflectance is the highest on the sunlit side of trees,
and lowest on the shade side”
Spatial distribution – Vertical loop and aligned with the solar azimuth direction
Results:
- Points ‘1’, ‘2’, ‘3’, ‘4’, ‘5’ in the frontal sunlit area of the tree had high transflectance levels, while point ‘4’ (60° looking downwards) had the maximum transflectance values
- However, the point which holds the maximum transflectance value changed throughout the day, as transflectance value of the sunlit area at different viewing angles varied with solar time
- Other points had relatively lower transflectance values
“The strongest tree crown transflection was found primarily towards the sky on the sunlit side of trees rather than towards the zenith”
Spatial distribution – Vertical loop perpendicular to the solar azimuth direction
Results:
- Point ‘3’, in the frontal sunlit area of the tree had the highest transflectance level, while other points lower transflectance values.
“Confirms that the strongest tree crown transflection was found primarily towards the sky on the sunlit side of trees rather than towards the zenith”