MAPPING SNOW ALGAE CONCENTRATIONS IN THE SIERRA NEVADA WITH IMAGING SPECTROSCOPY

We present spectral reflectance measurements of algal snow and a model to retrieve snow algal concentration from imaging spectrometer data collected in the Tioga Pass region of the Sierra Nevada, California. Spectral reflectance measurements of snow containing the algae Chlamydomonas Nivalas exhibit carotenoid absorption in the wavelength range 0.4 — 0.58 pm and chlorophyll—a,-b absorption in the wavelength range 0.6 — 0.7 pm. The integral of the scaled chlorophyll-a,-b absorption feature, 1680, varies with algal concentration, Ca. The relationship appears to be exponential but this model is not yet statistically significant due to limited data at high concentrations. Using the relationship, Ca = 922.61 exp(13.56 Isub680), we inverted Airborne Visible Imaging Spectrometer (AVIRIS) data for algae concentration. In the 5.5 km , imaged region, the mean algal concentration was 880 cells/mL with a standard deviation of 1445 cells/mL. We calculated the total imaged algal biomass, Ba = 11.1 kg. From the field spectral measurements, we fit a model relating snow albedo, AsubS, to Ca. We inverted algae concentration images for albedo using this model. Mean retrieved albedo was 0.595 with a standard deviation of 0.009, a minimum of 0.43, and a maximum of 0.62.