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CRC PUBLICATIONS |
Optical Properties of Leaves in the Visible and Near Infra-Red Under Beam and Diffuse Radiance
Iain Hume,
Tim McVicar,
Michael Roderick
Publication Type:
Technical Report
This is a publication of the current CRC for Catchment Hydrology
CRC Program:
Predicting Catchment Behaviour
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Publication Keywords:
Leaves (of Plants)
Optical Properties
Light
Infrared Analysis
Diffusion
Remote Sensing
Satellite Imagery
Reflection
Shade
Habitat
Vegetation
Radiometry
Instrumentation
Landsat
AVHRR
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Abstract / Summary:
Methods and equipment were developed to measure the directional transmittance and hemispherical reflectance and transmittance of diffuse light. The hemispherical reflectance (p), absorptance (a) and transmittance (t) of both beam and diffuse light by dicot and monocot leaves of varying thicknesses was estimated. Measurements were made at 1 nm increments in the visible and NIR parts of the spectrum (350-2500 nm).
Transmittance of diffuse light was aniostropic with more light was transmitted at angles close to the leaf surface normal. We found both dicot and monocot leaves exhibited this focusing of diffuse light. Dicot leaves transmitted a greater proportion of red and NIR light than monocot leaves at incidence angles up to 60o from the leaf normal. However, there were no differences in the hemispherical transmittance of dicot and moncot leaves.
The hemispherical reflectance of beam and diffuse light was almost identical at all wavelengths. Leaf thickness had minimal effect on the p, t, and a. The reflectance of beam near-infrared light by grass or tree leaves was statistically the same (P = 0.05). We conclude then that tree and understory leaves cannot be distinguished by their remotely sensed broad-band reflectance.
At visible wavelengths the optical properties of leaves were the same under either beam and diffuse illumination with most light (c. 85%) being absorbed. However, in the near-infrared, the optical properties depended on whether the incident light was beam or diffuse. The reflection of beam and diffuse near-infrared light were similar (c. 5%) but the absorption of diffuse light was much higher (23%) than of beam light (5%). This finding is consistent with the strong angular dependence of leaf optical properties in the near infrared. This result has important implications for modeling the energy balance of plant canopies.
This report is available for downloading below. Printed copies of the report can be purchased from the Centre Office. (Price $27.50 per copy).
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Centre Office:
CRC for Catchment Hydrology
Dept of Civil Engineering
Building 60
Monash University Vic 3800
Tel: +61 3 9905 2704
Fax: +61 3 9905 5033
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