Conifer shoot bidirectional scattering: methodology and preliminary results

Biophysical models describing radiant energy partitioning at the surface are dependent on our knowledge of the distribution of radiation on canopy elements and resulting interactions (i.e., reflectance, transmittance and absorptance) as well as on the existing state of coupled physiological parameters (such as stomatal conductance and photosynthesis). However, research on optical properties of coniferous forest canopy elements, particularly at the conifer shoot level, has been limited. The objective of this paper is to describe the methodology developed in the investigation of scattering from boreal forest conifer shoots and to present preliminary results using the methodology. An automated goniometer system and procedure were developed for characterizing the bidirectional scattering of conifer shoots. The system includes a computer-controlled goniometer, an SE-590 spectroradiometer, projected area device, sample stand, reference panel and artificial light source. Preliminary results of conifer shoot scattering indicate backscattering and forward scattering features specific to illumination-view-shoot geometries. The methodology presented offers an automated and fairly simple means of characterizing the bidirectional scattering from canopy elements where numerous measures are required. Such measurements are important in advancing our understanding regarding the dynamics of shoot-level absorptance of solar energy for physiological processes and interpreting remotely-sensed canopy reflectance in radiative transfer parameterization