OC3522Summer 2001 OC3522 - Remote Sensing of the Atmosphere and Ocean - Summer 2001 Scattering by...
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Transcript of OC3522Summer 2001 OC3522 - Remote Sensing of the Atmosphere and Ocean - Summer 2001 Scattering by...
![Page 1: OC3522Summer 2001 OC3522 - Remote Sensing of the Atmosphere and Ocean - Summer 2001 Scattering by Clouds & Applications.](https://reader035.fdocuments.in/reader035/viewer/2022062422/56649e8e5503460f94b91b22/html5/thumbnails/1.jpg)
OC3522OC3522 - Remote Sensing of the Atmosphere and Ocean - Summer 2001Summer 2001
Scattering by Clouds & ApplicationsScattering by Clouds & Applications
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Clouds droplets form when air parcels reach critical supersaturation (RH>100%) and water vapor condenses on aerosol particles, growing them to large enough sizes where vapor continues to condense.
http://atmos.es.mq.edu.au/AMOS/weatherwatch/photos/1995/0129mb08.jpg
This allows droplets to grow to sizes that are on the order of 100 times larger than aerosol particles.
The change in particle cross-section (r2) then increases by a factor of 104 !
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10-2
10-1
100
101
102
103
103
4
3
2
1
101
10-1
10-3
0.02
0.06
0.04
Radius (m)0.1 1.0 10.0
r2
Qs
n(r)
ds/dr = r2 Qs n(r)
10-2
10-1
100
101
102
103
103
4
3
2
1
101
10-1
10-3
2
6
4
Radius (m)0.1 1.0 10.0
Cloud Droplets
No Color Separation
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Why does a cloud appear white in visible imagery?
In VIS - cloud droplets are geometric scatterers - Qs ~ 2; s ~ 0.1m-1
The distribution of cloud droplet sizes with large values of = 2r/s, all are scattered equally
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This increase in s results in cloud optical depths between about 10 and 80.
Therefore the forward RT problem relies on a very complicated path radiance term:
€
Lt(λ,Θ,Φ) = L0(λ,Θ,Φ)e-δ(λ)/μ +γs(r,r',λ,X)L(r',λ,X)dΩ
4π∫
σ e(λ,z)e-δ(λ,z)/μ
0
δ(λ)
∫ dδμ
Since the radiance from all directions is required.
Path radiance
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The composition of clouds (liquid water or ice crystals) controls the potential for absorption as solar photons transfer through a cloudy atmosphere. The single scatter albedo (0) describes this potential and is determined by the imaginary index of refraction:
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The physical attributes of a cloud that control reflectance then includes:
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CLOUD TYPESWhen clouds are present: indicator of presence of moisture and cooling mechanisms
cause of cooling: - upward motion, radiative cooling, advection
Categories of clouds: 1) Low level (< 3 km)
2) Middle Level (3-7km) 3) High Level (7-12km)
4) Precipitating cloud: Nimbus
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Current Western US - 1kmCurrent GOES-10 Full Disk
Information available in Visible Imagery:
Brightness
DARK BRIGHT
Ocean
Land
Snow/Ice
Cumulonimbus
Cumulus
Stratus/StratocumulusCirrus
Locale
Texture
Cu Ci St, Cb
Climate Zones Seasons others… Synoptic Weather PersistenceDiurnal Cycles Surface Observations
Shadows
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altostratus
Examples from Euromet satellite meteorology page
stratus cumulonimbus cirrus
VIS
IR
IR
VIS
stratocumulus
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Threshold value is chosen at which anything brighter or colder - pixel is a cloud used in SST analysis
Problems with this method
Histogram shows clusters of values that represent surface or clouds
Pattern Recognition use of area means and standard
Cloud detection & Classification
Spatial coherence
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http://atmos.es.mq.edu.au/AMOS/weatherwatch/photos/1991/0120mb04.jpghttp://atmos.es.mq.edu.au/AMOS/weatherwatch/photos/1995/0205mb12.jpg
http://atmos.es.mq.edu.au/AMOS/weatherwatch/photos/1996/0731jd24.jpg http://www.cira.colostate.edu/
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http://atmos.es.mq.edu.au/AMOS/weatherwatch/photos/1991/0120mb01.jpghttp://atmos.es.mq.edu.au/AMOS/weatherwatch/photos/1995/0129mb08.jpg
http://atmos.es.mq.edu.au/AMOS/weatherwatch/photos/1996/0731jd09.jpghttp://www.orbimage.com/main/imgweek/highsnow01_99_2ns.jpg
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http://atmos.es.mq.edu.au/AMOS/weatherwatch/photos/1995/0415jd01.jpg
http://earth.jsc.nasa.gov/lores.cgi?PHOTO=STS043-076-061
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http://atmos.es.mq.edu.au/AMOS/weatherwatch/photos/1996/0731jd23.jpghttp://atmos.es.mq.edu.au/AMOS/weatherwatch/photos/1996/0731jd38.jpg
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Hurricane MitchHurricane Mitch
http://rsd.gsfc.nasa.gov/rsd/images/Mitch/mitch3_lg.jpg