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ESM 266: Remote sensing of water 1
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ESM 266: Remote Sensing of
Water
Jeff Dozier
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Earth: the water planet
By volume, 96% in oceans, 3% in snow and
ice, 1% in ground water
74% of surface
Components of reflectance from water
Total radiance, (Lt) recorded by
a remote sensing system over
water is a function of the
electromagnetic energy receivedfrom:
Lp = atmospheric path radiance
Ls = free-surface layerreflectance
Lv = subsurface volumetricreflectance
Lb = bottom reflectance
Total radiance, (Lt) recorded by
a remote sensing system over
water is a function of the
electromagnetic energy received
from:
Lp = atmospheric path radiance
Ls = free-surface layerreflectance
Lv = subsurface volumetricreflectance
Lb = bottom reflectance
Absorption
and
scattering in
pure water
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Examples: dark in NIR, sunglint
Black and white infrared photograph
of water bodies in Florida
Black and white infrared photograph
of water bodies in Florida Black and white infrared
photograph with sunglint
Black and white infrared
photograph with sunglint
Water penetration
SPOT Band 1 (0.5 -0.59 m) green
SPOT Band 1 (0.5 -0.59 m) greenSPOT Band 2 (0.61 -0.68 m) red
SPOT Band 2 (0.61 -0.68 m) redSPOT Band 3 (0.79 -0.89 m) NIR
SPOT Band 3 (0.79 -0.89 m)NIR
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Spectral response of water
Inorganic and organic suspensions Particles range from fine clay (3-4mm), to silt (5-40
mm), to fine-grain sand (40-130mm), and coarse grainsand (131 - 1250 mm)
Concentrated in the inland and nearshore water bodies
Clear, deep ocean (Case 1 water) far from shore rarelycontains suspended minerals greater than 1mm indiameter
Plankton Chlorophyll a is a reasonable surrogate
Dissolved organic matter Related to phytoplankton production
Gelbstoff(yellow stuff)
Field measurementsclay
clay
silt
silt
400 450 500 550 600 650 700 750 800 850 9000
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Wavelength (nm)
PercentReflectance
50
100
150
200
250
clear water
400 450 500 550 600 650 700 750 800 850 9000
Wavelength (nm)
2
4
6
8
10
12
14
PercentReflectance
300
1,000 mg/l
1,000 mg/l
600
clear water
50
100
150
200250
300350
400
450500550
a.
b.
Clayey soil
Silty soil
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ESM 266: Remote sensing of water 3
Suspended sediments
MississippiDelta,
12/27/2001
http://visibleearth.nasa.gov/
Reflectance of algae-laden water
400 500 600 700 800 900
0
0.5
1
1.5
2
2.5
3
3.5
4
Wavelength (nm)
PercentReflectance clear
water
5
10
15
20
25
PercentReflectance
a.
algae-laden
water
400 500 600 700 800 900
0
Wavelength (nm)
b.
500 mg/l
0 mg/l
Algae-Laden Water with Various
Suspended Sediment Concentrations
Note the strong chlorophyll a absorption
of blue light between 400 and 500 nm
and of red light at approximately 675
nm
Chlorophyll a fall 1997, g/m3
W. Gregg and N. Casey, GSFC
Independent validation of
MODIS chlorophyll
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Aqua: 1840Terra: 1535
Chlorophyll a Feb 26, 2003
Floods in western Australia, Jan 2003
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Aqua: 1840Terra: 1535
Daytime SST Feb 26, 2003
differences partially due to diurnal warming
Sea surface temperature, March 4, 1999
Adjusted to highlight nearshore
temperature differences
Adjusted to highlight nearshore
temperature differencesAdjusted to highlight Gulf Stream
temperature differences
Adjusted to highlight Gulf Stream
temperature differences
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Gulf Stream temperatures from MODIS, May
2, 2001
MODIS global sea-surface temperature, May
2002
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Scatterometry (Seawinds)