Seasonal changes observed in AVIRIS images of Jasper Ridge, California

The authors examined three 1992 Airborne Visible Infrared Imaging Spectrometer (AVIRIS) images of Jasper Ridge Biological Preserve (JRBP) for spectral changes associated with community type and for phenological patterns over the growing season. The images were obtained on June 2, September 4, and October 6, 1992 and were calibrated to surface reflectance. Images were analyzed with spectral mixture analysis using library endmembers representing green foliage, non-photosynthetic vegetation, and soils characteristic of the site. The images were co-registered in a Geographic Information System (GIS), along with a digital elevation model (DEM) of the Menlo Park 7.5 min. Quandrangle obtained from US Geological Service and a field-based vegetation map provided by the JRBP. Vegetation endmember fractions were used to define vegetation communities and compared to the field-based vegetation map. Because there the terrain did not have steep north and south facing slopes, adding a DEM to the analysis did not increase accuracy of the classification. Vegetation fractions can be related to patterns expected for wetlands and grasslands, and for evergreen and deciduous shrub and tree communities. After vegetation boundaries were defined using the field-based map, the authors extracted the mean vegetation spectrum and standard deviation of the spectrum for each vegetation type. Changes in AVIRIS spectra over the season were compared among communities and these spectra were compared to field-based reflectance and biochemistry measurements of foliage that were representative of each community over the same seasonal period