Spatial and temporal variability of surface cover at BOREAS using reflectance from a helicopter platform

Helicopter-based radiometric measurements of forested sites acquired during the Boreal Ecosystem-Atmosphere Study (BOREAS) were used to examine the spatial, temporal, and spectral variability in surface reflectance and vegetation indices (VI), including the normalized difference vegetation index (NDVI) and the simple ratio (SR), and for comparison with surface cover and fluxes. Of the two VIs examined, results showed that the NDVI offered more predictive information than the SR regarding temporal and spatial variations in surface characteristics. Linear regression analyses between the surface biophysical measurements and the helicopter reflectances and VIs resulted in low r² values (consistently < 0.5), which may be explained by the effects of incomplete canopy cover and background effects. Only among sites that were mainly vegetated by Aspen (Populus tremuloides) and observed during the summer IFC was a stronger relationship observed.