Remote sensing of snow in visible and near-infrared wavelengths 3/28/2012 Remote sensing of snow in visible and near-infrared wavelengths Jeff Dozier – UCSB NASA Snow Remote Sensing Workshop Boulder, August 2013 ESM 236: Remote sensing of snow

Different concepts in different parts of spectrum Visible, near-infrared, and infrared Independent scattering Weak polarization Scalar radiative transfer Penetration near surface only ~0.3 m in blue, few mm in NIR and IR Small dielectric contrast between ice and water Microwave and millimeter wave Extinction per unit volume Polarized signal Vector radiative transfer Large penetration in dry snow, many m Effects of microstructure and stratigraphy Small penetration in wet snow Large dielectric contrast between ice and water

Optical properties of ice & water — visible and near-infrared wavelengths (Warren, Applied Optics, 1982) wavelength, m

N=n+ik, Index of refraction (complex) dx I0 I

Basic scattering properties of a single grain Mie theory, based on N and x=2r/  — single-scattering albedo g — asymmetry parameter Qext— extinction efficiency

Snow is a collection of scattering grains

Snow spectral reflectance and absorption coefficient of ice

Spectra with 7 MODIS “land” bands (500m resolution, global daily coverage)

Landsat Thematic Mapper (TM, on Landsats 4,5,7) 30 m spatial resolution 185 km FOV 16 day repeat pass Landsat 8 launched in February 2013

Landsat snow-cloud discrimination Bands 5 4 2 (V,nIR,swIR) Bands 3 2 1 (visible) Benefit of shortwave-infrared Landsat snow-cloud discrimination

MODIS: similar bands, wider swath (2300 km), bigger pixels (500 m), daily coverage

Snow cover from MODIS

Comparison of MODIS (500m) and Landsat (30m) fSCA 32 scenes with coincident MODIS and Landsat images Average RMSE = 7.8% Range from 2% to 12%

Cloudy, 20%-80% depending on where/when