NASA Airborne Snow Observatory: Analysis of Snow Algae in the Sierra Nevada Snowpack

Seasonal snowfields host a variety of microbial life including snow algae that perform microbiological processes such as heterotrophy, photosynthesis and nutrient cycling when the snow melts. A previous study (Painter et al 2001) performed detection and quantification of snow algae using the National Air and Space Administration/Jet Propulsion Laboratory Airborne Visible Infrared Imaging Spectrometer (AVIRIS) to estimate algal biomass at the snowfield scale. Spectral reflectance measurements in snow containing algae show carotenoid absorption and chlorophyll absorption at wavelengths of approximately 0.55 and 0.68 mm. The Painter algorithm was able to spatially quantify snow algae concentration and create a model to predict algae concentration based on subsequent reflectance spectra.

In the spring of 2017, the Sierra Nevada of California had anecdotally the largest expanse of snow algae in known history. While the Painter algorithm was developed on data from the Sierra Nevada, this leveraged a single acquisition and pointed the way to performing scientific inquiry on snow algae processes. Fortunately, the NASA Airborne Snow Observatory (ASO) acquired many acquisitions throughout the central Sierra Nevada across many springs/summers, including those of 2017. ASO uses an imaging spectrometer and scanning LiDAR system to quantify snow depth, snow water equivalent and snow albedo. This presentation will describe data collected in the central Sierra Nevada using the ASO platform across multiple years. The retrievals will include the estimation of the imaged biomass based on the Painter model and a physiographic analysis of the controls on algae concentrations across the mountain landscape and how those change with time.

This analysis of snow algae with imaging spectroscopy lays groundwork for coming Earth and planetary NASA spectrometer missions. Among these are the 2017 Earth Science Decadal Survey Surface Biology and Geology concept, for which understanding Earth's snow spectral albedo and its controls was a motivating objective and the coming Mapping Imaging Spectrometer for Europa (MISE) that will fly on the NASA Europa Clipper in the next decade to explore habitability and distributions of potential extremophiles or remnant life forms embedded in the Europan ice surface.