Canopy Structure and Spectral Leaf Albedo from Multiangular Imaging Spectroscopy

Imaging spectroscopy, or hyperspectral remote sensing, has great potential in environmental monitoring. Among many application areas, this technology has large potential for monitoring the status and functioning of forest at regional to global scales, for both environmental and commercial purposes. The reflectance signal of a vegetation canopy measured by an imaging spectrometer can be viewed as consisting of biochemical and structural components. The former corresponds to leaf reflectance which depends on the concentration of optically active pigments. The latter is formed as the biochemical signal is modulated in the vegetation layer as photons interact with canopy elements (leaves or needles) multiple times. To make best use of the measured spectral reflectance of a forest, the structural and biochemical components of total reflectance should be separated. The problem can also be posed as follows: if we could separate the contribution of photons which have interacted with vegetation canopy only once, we could measure the biochemical signal. The remainder, or the multiple scattered reflectance component, depends on the amount and structure of vegetation. In this study, the separation of forest reflectance into first and higher scattering orders is achieved using multiangular remote measurements. The first-order scattering component is shown to depend linearly on the single-scattering albedo of leaves. Multiple scattering behaves in a more complex manner and no direct conclusions can be drawn. However, the effects of canopy structure are visible in the decomposed signal.