Bidirectional spectral reflectances measured above coniferous forests from a ground-based platform

摘要

Spectral reflectances were acquired above three different coniferous forest stands. Continuous visible/near-infrared (0.400 - 1.100 $mu@m) spectra were collected at multiple (8 - 12) view angles in the solar principal plane by a spectroradiometer (SE590, Spectron Engineering, Denver, CO) placed on ground-based platforms that extended above the forest tops. Data were collected over a full sun angle range in August 1991 above a 14 m high mixed spruce-hemlock stand at a research site managed by the University of Maine in Howland. Data were also collected at multiple sun angles in June/July 1992 at the Petawawa National Forest Institute in Petawawa, Ontario, Canada above two stands: a 14 m high jack pine stand and a 18 m high red pine stand. Reflectances were calculated from calibrated radiances, and corrected for panel anisotropy per sun angle. As a function of view angle per sun angle, forwardscatter and backscatter spectra from all sites were used to compute vegetation indices and Photosynthetically Active Radiation (PAR, 0.400 - 0.700 $mu@m) reflectance. These unique data sets reveal that these forest stands were highly anisotropic, both in terms of sun angle, view angle, and spectral wavebands. Additionally, the vegetation indices exhibited sun and view angle changes, with maximum values at moderately oblique forwardscatter view angles (approximately 30 - 40$DGR@).