Measuring Spatial Distribution of Snow Water Equivalent and Snow Albedo

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The two most critical properties for understanding snowmelt runoff and timing are the spatial and temporal distributions of snow water equivalent (SWE) and snow albedo. Despite their importance in controlling volume and timing of runoff, snowpack albedo and SWE are still largely unquantified in the US and not at all in most of the globe, leaving runoff models poorly constrained. NASA/JPL, in partnership with the California Department of Water Resources, has developed the Airborne Snow Observatory (ASO), an imaging spectrometer and scanning lidar system, to quantify SWE and snow albedo, generate unprecedented knowledge of snow properties for cutting edge cryospheric science, and provide complete, robust inputs to water management models and systems of the future.


Funding provided by NASA Terrestrial Hydrology, NASA Applied Sciences, and California Department of Water Resources


MAPS


SWE 2014 Slow-Motion

Albedo 2014 Slow-Motion

Instruments

NASA/JPL has created the Airborne Snow Observatory (ASO), a coupled imaging spectrometer and scanning lidar system. ASO uses the imaging spectrometer to quantify spectral albedo, broadband albedo, and radiative forcing by dust and black carbon in snow. The scanning lidar is used to determine snow depth against snow-free acquisitions and quantifies snow water equivalent when combined with in-situ constrained modeling of snow density.

Spectrometer
Imaging Spectrometer

Imaging Spectrometer

ASO uses an ITRES CASI-1500 imaging spectrometer, which captures imagery in 72 spectral bands from the visible to the near-Infrared. Ground pixel size is approximately 2m from a flight altitude of 15,000ft above ground level. This provides spectral albedo of the snow surface, which is used to determine the energy absorbed from incoming sunlight. This, combined with energy balance modeled from meteorological conditions, yields snowmelt rates.

LIDAR
LIDAR

LIDAR

ASO uses a Riegl Q1560 scanning lidar, which captures the surface topography with < 10 cm vertical accuracy. Depth is calculated by subtracting a summer “snow-free” dataset from each winter “snow-on” dataset. The accuracy of these data is dependent upon precise knowledge of the aircraft position during the measurements. An integrated Applanix Inertial Measurement Unit (IMU) and GPS provide aircraft attitude and position information, and this information is combined with error corrections from an existing network of GPS base stations at fixed locations near the survey area. This combined use of the IMU for high-speed attitude information, along with the differential GPS solution for absolute position, yields the sub-decimeter aircraft trajectory accuracy necessary for LiDAR snow depth measurements.

Media

New Technology Measures Snowpack Amid California Drought
National Geographic - August 5, 2014
Finding Water in Snow
Earth Observatory - April 3, 2014
Yosemite's largest ice mass is melting fast
Los Angeles Times - October 01, 2013
How soot killed the Little Ice Age
Nature - September 02, 2013
NASA Opens New Era in Measuring Western U.S. Snowpack
The Daily Camera - March 08, 2013
Dan Goods, JPL's science seer
Los Angeles Times - February 20, 2013
Global Warming Might Threaten Water Supply
Voice of America - November 11, 2012

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