Terra MODIS & S-NPP VIIRS Observe Snowpack in Sierra Nevada Mt. Range
The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor is located aboard NASA’s Terra and Aqua satellites. The Visible Infrared Imaging Radiometer Suite (VIIRS) sensor is aboard the Suomi National Polar-orbiting Partnership (S-NPP) satellite. Together these sensors provide us with over two decades of crucial data for studying changes that have occurred on the surface of the Earth, including times of drought.
This video uses images produced from Terra MODIS and S-NPP VIIRS Surface Reflectance data over the Sierra Nevada Mountain Range to show changes in the snow cover from 2000 to 2021. You might notice these images of the Earth don’t look like we typically see using our eyes. looks like to our eyes. That is because these images are shown using band combinations that highlight snow and ice on the Earth’s surface. For Terra MODIS this band combination is 3-6-7 for S-NPP VIIRS it is M3-I3-M11. These band combinations are used to map snow and ice because these features are very reflective at blue wavelengths in the visible part of the electromagnetic spectrum and are absorbed at SWIR wavelengths. This helps us identify snow from ice and clouds.
Here snow and ice will appear as bright red-orange, vegetation as green, bare soil and deserts as bright cyan, clouds as white, and water as dark blue or black. In the Terra MODIS images small ice crystals in high-level clouds will appear a peach, whereas in the S-NPP VIIRS images they will appear as pink. Observe the interannual variation in the snow cover (red) as the video progresses through the images for each year, allowing scientists and water managers to see how much snow cover existed in the Sierra Nevada mountains each year. Scientists use in-situ measurements of snowpack as a key indicator of drought, as the water from the melting snowpack is a source of fresh water for Californians.
The California Department of Water Resources measures the snowpack in the mountains every year on April 1, to provide consistent data and to study the size of the snowpack. Notice how in the drought years, for example 2003 and 2015, the snowpack is smaller in size than it is during the wetter years, for example 2005 and 2019. In 2021, the snowpack was measured by scientists at 61 percent of the historical average, indicating a drier year. A smaller snowpack in spring can be problematic during times of drought, as water resources for California residents can be limited.
To learn more about these data and other data products distributed by the LP DAAC, please visit https://lpdaac.usgs.gov/.
The Land Processes Distributed Active Archive Center (LP DAAC) is one of the NASA Earth Observing System Data and Information System (EOSDIS) DAACs and operates as a partnership with the United States Geological Survey (USGS). It is located at the USGS Earth Resources Observation and Science (EROS) Center in Sioux Falls, South Dakota. Want to learn more about data from the LP DAAC? Sign up for the LP DAAC listserv: https://lists.nasa.gov/mailman/listinfo/lpdaac