Spectral detection of subarctic vegetation phenophases

Boreal and subarctic plant phenophases are good indicators of global climatic change. Ground information is needed for satellite remote sensing to assess plant phenophases. A boom-mounted four-band spectroradiometer was installed to observe shrub canopies during the 1994 growing season in northernmost Finland. It measured the reflectance factors of four fixed ground plots each once an hour in green (520-600 nm), red (630-690 nm), near-infrared (765-900 nm) and midinfrared (1570-1730 nm) spectral bands. The turning point dates (date when the slope, or trend in time of the reflectance curve changes) of seasonal near-infrared (765-900 nm) and red (630-690 nm) reflectance factors indicated the end of growth and beginning of autumn changes of shrubs, respectively. The ratio of green (520-600 nm) and red (630-690 nm) band reflectance factors, however seemed to be more accurate in estimating them.