Applications of Satellite Derived
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Applications of Satellite Derived Ocean Surface Vector Winds in
Operational Marine Weather Forecasting
Joe Sienkiewicz, NOAA/NWS Ocean Prediction CenterZorana Jelenak, UCAR/NOAA NESDIS
How is Wind Measured Over the Ocean?
Direct Measurements
• Buoy, Ships– Pros
• Provide frequent updates at a single point, meeting or exceeding 1-hr refresh
• Provide reference points for real-time diagnostics in the generation of the forecast/warning package
• Complements synoptic scale satellite information by providing a frequently updated reference measurement
– Cons• Limited coverage – only provide limited point measurements
Indirect Measurements
OSCAT Descending Passes
ASCAT Descending Passes
Wind speed and direction information needs to be derived from satellite measurements
NSCAT
August 1996
Wind Vector Measurements Through History
Stick
Scatterometer
ERS 1 & 2
Aug 1991, April 1995
Stick
Scatterometer
SeaSAT 1978
110 days
SeaWinds+AMSR
Dec 2002
Pencil-beam
Scatterometer
QuikSCAT
June 1999-Nov 2009
Stick
ScatterometerASCAT-B
Sep 2012
C-band
Ku-band
Pencil-beam
Scatterometer
OceanSat-2
Sep 2009
ASCAT
Oct 2006
What are Scatterometers?• Microwave Radars on Polar orbiters
– C-band ~5GHz (~5cm), Ku-band ~14GHz (~2cm)
• C-band (less impacted by rain than Ku)
• Ku-band (rain impact)
– designed to measure ocean surface backscatter (0 )• Capillary waves• infer wind speed
– Multiple samples from different azimuth angles
• wind direction solutions
t
r0 P
PG
Pr
Pt
Surface roughness relates to 0 and depends on friction velocity
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QuikSCAT Measurement Geometry
WVC – Wind Vector Cell
25km → 76 WVC across swath
Far Swath Far SwathMid Swath Mid SwathNadir
H-pol
V-pol
4 observations good azimuth diversity
4 observations poor azimuth diversity
2 observations
Measurement GeometryMeasurement Geometry
4-Look Solution
Most likely solution U=10m/s, χ=150°
16 December 2009
Rain EffectsRain Effects
• The radar signal is attenuated by the rain as it travels to and from the Earth’s surface σ0
•Retrieved wind speed
The radar signal is scattered by the raindrops. Some of this scattered energy returns to the instrument σ0
•Retrieved wind speed
•The roughness of the sea surface is increased because of the splashing due to raindrops σ0
•Retrieved wind speed•Directional information can be lost
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A S C A T
T R A C K
O S C A T
T R A C K
Rain Impact on OSCAT RetrievalsCase 1
Rain Impact on OSCAT RetrievalsCase 1
Examples
ASCAT 2100 UTC 02 NOV 2012
GDAS 2100 UTC 02 NOV 2012
NOAA Ocean Prediction Center – scatterometer impacts on operations
OSCAT and ASCAT Forecasters use every pass to: make warning and short-term forecast decisions and to estimate - cyclone location, intensity, extent of wind field - strength and extent of orographically enhanced jets - wind field near strong SST
gradientsResults in improved warning and forecast services over otherwise data sparse oceans
SUPER STORM Sandy – ASCAT 1419 UTC29 Oct 2012
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