1. 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

2. 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

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

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

5. 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

6. Snow is a collection of scattering grains

7. Snow spectral reflectance and absorption coefficient of ice

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

9. 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

10. Landsat snow-cloud discrimination
Bands (V,nIR,swIR)
Bands (visible)
Benefit of shortwave-infrared
Landsat snow-cloud discrimination

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

12. Snow cover from MODIS

13. 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%

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