Space-Time Series of MODIS Snow Cover Products Jeff Dozier, James E Frew, Thomas H Painter

Topics Spectral reflectance of snow and its variability Implications for energy balance of snowpack Remote sensing of snow-covered area and albedo Fractional (subpixel) snow cover and grain size from MODIS, every day Time series corrections for clouds, viewing geometry, and other noise Available for use by others for hydrologic models

Seasonal solar radiation, Mammoth Mountain

Snow is a collection of scattering grains

Snow spectral reflectance and absorption coefficient of ice

Spectra with MODIS “land” bands

MODIS image of Sierra Nevada EOS Terra MODIS 07 March 2004 MOD09 Surface Reflectance 0.555 0.645 0.858

Snow covered-area and grain size – Sierra Nevada (the MODSCAG model)

Spectral mixture analysis, generalized Spectral mixture equation, per pixel Spectral residuals, per pixel RMS error, per pixel MODSCAG spectrally mixes with range of snow endmembers and chooses the result with the least RMS error for that pixel

Based on work with AVIRIS: Snow-covered area in the Tokopah Basin (Kaweah River drainage) 21 May 1997 05 May 1997 18 June 1997 20 km

Grain size in the Tokopah Basin (Kaweah River drainage) 21 May 1997 05 May 1997 18 June 1997 20 km

Analysis of MODIS data for a single day

But some days are cloudy

Noisy variability caused by look angle, small clouds, vegetation, topography detail Vegetation causes differences in view angle

Variability of snow cover and grain size at a pixel

Need to interpolate and smooth to fill the space-time cube Raw snow cover Interpolated snow cover

Time series, Tuolumne basin, Oct 2004 – July 2005

Comparison of fractional snow cover with “binary” (pixel snow-covered when f ≥ 0.5)

Products available from the Snow Server http://www.snow.ucsb.edu Fractional snow-covered area, grain size (and contaminants) from daily MODIS images Quality flags for cloud cover, highly oblique viewing Fractional coverage of other endmembers Best estimate of snow-covered area and broadband albedo on that date Extrapolating from previous values to that date and smoothing End-of-season reanalysis of daily snow-covered area and broadband albedo Interpolation, smoothing, comparison with in situ snow pillow data

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