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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

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1

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2

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3

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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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Suspended sediments

MississippiDelta,

12/27/2001

http://visibleearth.nasa.gov/

Reflectance of algae-laden water

400 500 600 700 800 900

0

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2

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3

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Wavelength (nm)

PercentReflectance clear

water

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10

15

20

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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


Adjusted to highlight Gulf Stream



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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)

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