We describe spectral reflectance measurements of snow containing the snow a
lga Chlamydomonas nivalis and a model to retrieve snow algal concentrations
from airborne imaging spectrometer data. Because cells of C. nivalis absor
b at specific wavelengths in regions indicative of carotenoids (astaxanthin
esters, lutein, beta -carotene) and chlorophylls a and b, the spectral sig
nature of snow containing C. nivalis is distinct from that of snow without
algae. The spectral reflectance of snow containing C. nivalis is separable
from that of snow without algae due to carotenoid absorption in the wavelen
gth range from 0.4 to 0.58 mum and chlorophyll a and b absorption in the wa
velength range from 0.6 to 0.7 mum. The integral of the scaled chlorophyll
a and b absorption feature (I-0.68) varies with algal concentration (C-a).
Using the relationship C-a = 81019.2 I-0.68 + 845.2, we inverted Airborne V
isible Infrared Imaging Spectrometer reflectance data collected in the Tiog
a Pass region of the Sierra Nevada in California to determine algal concent
ration. For the 5.5-km(2) region imaged, the mean algal concentration was 1
,306 cells ml(-1), the standard deviation was 1,740 cells ml(-1), and the c
oefficient of variation was 1.33. The retrieved spatial distribution was co
nsistent with observations made in the field. From the spatial estimates of
algal concentration, we calculated a total imaged algal biomass of 16.55 k
g for the 0.495-km(2) snow-covered area, which gave an areal biomass concen
tration of 0.033 g/m(2).