Presentation Transcript
Quick Review of Remote Sensing Basic Theory Paolo Antonelli CIMSS University of Wisconsin-Madison South Africa, April 2006: Quick Review of Remote Sensing Basic Theory Paolo Antonelli CIMSS University of Wisconsin-Madison South Africa, April 2006
Outline: Outline Visible: RGB, Radiance and Reflectance
Near Infrared: Absorption
Infrared: Radiance and Brightness Temperature
Slide3: Visible
(Reflective Bands) Infrared
(Emissive Bands)
Sensor Geometry: Sensor Geometry Sensor Optics Electronics
Slide5: Terminology of radiant energy Energy from
the Earth Atmosphere
Slide6: Definitions of Radiation
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QUANTITY SYMBOL UNITS
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Energy dQ Joules
Flux dQ/dt Joules/sec = Watts
Irradiance dQ/dt/dA Watts/meter2
Monochromatic dQ/dt/dA/d W/m2/micron
Irradiance
or
dQ/dt/dA/d W/m2/cm-1
Radiance dQ/dt/dA/d/d W/m2/micron/ster
or
dQ/dt/dA/d/d W/m2/cm-1/ster
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Visible: Reflective Bands: Visible: Reflective Bands Used to observe solar energy reflected by the Earth system in the:
Visible between .4 and .7 µm
NIR between .7 and 3 µm
About 99% of the energy observed between 0 and 4 µm is solar reflected energy
Only 1% is observed above 4 µm
Slide13: Radiances
On Same
Color Scale
Reflectance: Reflectance To properly compare different reflective channels we need to convert observed radiance into a target physical property
In the visible and near infrared this is done through the ratio of the observed radiance divided by the incoming energy at the top of the atmosphere
The physical quantity is the Reflectance i.e. the fraction of solar energy reflected by the observed target
Slide16: Soil Vegetation Snow Ocean
Slide17: Reflectances
On Same
Color Scale
Slide19: Radiance observed
In the Blue Band
At 0.41 µm More than 75% of the
Observed energy
Over Ocean
In the blue bands
Is due to atmospheric
Scattering.
Less than 25% is due
to Water
Leaving Energy
Slide20: Band 4
(0.56 Micron) Band 1
Band 4
Band 3 Transects of Reflectance
Slide22: Band 20
1.38 micron
Strong H20
Slide23: Only High Clouds
Are Visible
Slide24: Band 20
1.38 micron
Slide25: Visible
(Reflective Bands) Infrared
(Emissive Bands)
Emissive Bands: Emissive Bands Used to observe terrestrial energy emitted by the Earth system in the IR between 4 and 15 µm
About 99% of the energy observed in this range is emitted by the Earth
Only 1% is observed below 4 µm
At 4 µm the solar reflected energy can significantly affect the observations of the Earth emitted energy
Slide27: Spectral Characteristics of Energy Sources and Sensing Systems IR 4 µm 11 µm
Observed Radiance at 4 micron: Observed Radiance at 4 micron Range [0.2 1.7] Values over land
Larger than over water Reflected Solar everywhere
Stronger over Sunglint Window Channel:
little atmospheric absorption
surface features clearly visible
Observed Radiance at 11 micron: Observed Radiance at 11 micron Range [2 13] Values over land
Larger than over water Undetectable Reflected Solar
Even over Sunglint Window Channel:
little atmospheric absorption
surface features clearly visible
Brightness Temperature: Brightness Temperature To properly compare different emissive channels we need to convert observed radiance into a target physical property
In the Infrared this is done through the Planck function
The physical quantity is the Brightness Temperature i.e. the Temperature of a black body emitting the observed radiance
Observed BT at 4 micron: Observed BT at 4 micron Range [250 335] Values over land
Larger than over water Reflected Solar everywhere
Stronger over Sunglint Window Channel:
little atmospheric absorption
surface features clearly visible Clouds are cold
Observed BT at 11 micron: Observed BT at 11 micron Range [220 320] Values over land
Larger than over water Undetectable Reflected Solar
Even over Sunglint Window Channel:
little atmospheric absorption
surface features clearly visible Clouds are cold
Conclusions: Conclusions Radiance is the Energy Flux (emitted and/or reflected by the Earth) which strikes the Detector Area at a given Spectral Wavelength (wavenumber) over a Solid Angle on the Earth;
Reflectance is the fraction of solar energy reflected to space by the target;
Given an observed radiance, the Brightness Temperature is the temperature, in Kelvin, of a blackbody that emits the observed radiance;
Knowing the spectral reflective (Vis) and emissive (IR) properties (spectral signatures) of different targets it is possible to detect: clouds, cloud properties, vegetation, fires, ice and snow, ocean color, land and ocean surface temperature ……