Angular reflectance of leaves with a dual-wavelength terrestrial lidar and its implications for leaf-bark separation and leaf moisture estimation

Hancock, S; Gaulton, R; Danson, FM

Abstract

A new generation of multi-wavelength lidars offer
the potential to measure the structure and biochemistry of
vegetation simultaneously, using range resolved spectra indices
to overcome the confounding effects in passive optical measurements.
However, the reflectance of leaves depends on angle of
incidence and if this dependence varies between wavelengths,
the resulting spectral indices will also vary with angle of
incidence, complicating their use in separating structural and
biochemical effects in vegetation canopies. The SALCA dualwavelength
terrestrial laser scanner (Salford Advanced Laser
Canopy Analyser) was used to measure the angular dependence
of reflectance for a range of leaves at the wavelengths used by the
new generation of multi-wavelength lidars, 1063 nm and 1545nm,
as used by SALCA, DWEL and the Optech Titan. The influence
of the angle of incidence on the Normalised Difference Index of
these wavelengths (NDI) was also assessed.
The reflectance at both wavelengths depended on the angle
of incidence, was non-Lambertian and could be well modelled
as a cosine. The change in NDI with leaf angle of incidence
was small compared to the observed difference in NDI between
fresh and dry leaves and between leaf and bark. Therefore it
is concluded that angular effects will not significantly impact
leaf moisture retrievals or prevent leaf/bark separation for the
wavelengths used in the new generation of 1063 nm and 1545
nm multi-wavelength lidars.

Citation

Hancock, S., Gaulton, R., & Danson, F. (2017). Angular reflectance of leaves with a dual-wavelength terrestrial lidar and its implications for leaf-bark separation and leaf moisture estimation. IEEE Transactions on Geoscience and Remote Sensing, 55(6), https://doi.org/10.1109/TGRS.2017.2652140

• Journal Article Type: Article
• Online Publication Date: Mar 15, 2017
• Publication Date: Mar 15, 2017
• Deposit Date: Feb 2, 2017
• Publicly Available Date: Apr 5, 2017
• Journal: IEEE Transactions on Geoscience and Remote Sensing
• Print ISSN: 0196-2892
• Publisher: Institute of Electrical and Electronics Engineers
• Volume: 55
• Issue: 6
• DOI: https://doi.org/10.1109/TGRS.2017.2652140
• Publisher URL: http://dx.doi.org/10.1109/TGRS.2017.2652140
• Related Public URLs: http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?reload=true&punumber=36