Post on 23-Feb-2016
description
transcript
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Remote sensing of snow in visible and near-infrared
wavelengths
Jeff Dozier – UCSBNASA Snow Remote Sensing Workshop
Boulder, August 2013
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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
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Optical properties of ice & water — visible and near-infrared wavelengths
refractive index (real)
1.16
1.18
1.20
1.22
1.24
1.26
1.28
1.30
1.32
1.34
0.4
0.8
1.2
1.6
2.0
2.4
icewater
refractive index (imag)
1.0E-10
1.0E-9
1.0E-8
1.0E-7
1.0E-6
1.0E-5
1.0E-4
1.0E-3
1.0E-2
0.4
0.8
1.2
1.6
2.0
2.4
icewater
e-folding distance, m
0.00001
0.0001
0.001
0.01
0.1
1
10
100
0.4
0.8
1.2
1.6
2.0
2.4
icewater
wavelength, m(Warren, Applied Optics, 1982)
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N=n+ik, Index of refraction (complex)
0 sinsin
i
r
cnc
ir
I0 I
dx
4
0
4
kx
dI k IdxI eI
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Snow is a collection of scattering grains
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Snow spectral reflectance and absorption coefficient of ice
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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
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Benefit of shortwave-infrared
Landsat snow-cloud
discrimination
Bands 3 2 1
(visible)
Bands 5 4 2
(V,nIR,swIR)
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MODIS: similar bands, wider swath (2300 km), bigger pixels (500 m), daily coverage
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Snow cover from MODIS
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Comparison of MODIS (500m) and Landsat (30m) fSCA
32 scenes with coincident MODIS and Landsat imagesAverage RMSE = 7.8%Range from 2% to 12%
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Cloudy, 20%-80% depending on where/when
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