noaa assessment of the oceansat-2 scatterometer
DESCRIPTION
NOAA Assessment of the Oceansat-2 Scatterometer. Seubson Soisuvarn Khalil Ahmad Zorana Jelenak Joseph Sienkiewicz Paul S. Chang. Introduction. NOAA has been receiving day old OSCAT data via ISRO dedicated FTP server since September 2010 - PowerPoint PPT PresentationTRANSCRIPT
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NOAA Assessment of the Oceansat-2 Scatterometer
Seubson Soisuvarn Khalil Ahmad
Zorana Jelenak Joseph Sienkiewicz
Paul S. Chang
9-11 May 2011 IOVWST Meeting, Annapolis, MD, USA 1
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IntroductionNOAA has been receiving day old OSCAT data via ISRO dedicated FTP server
since September 2010NRT OSCAT data flow from ISRO to EUMETSAT commenced in February 2011.
Since then EUMETSAT has been receives 12-14 orbits per day. In March 2011 NRT OSCAT data flow began at NOAA via EUMETSAT dedicated FTP server
NOAA is currently receiving all three levels of OSCAT data: L1B, L2A and L2BL2A and L2B
Gridded @ 50 km WVCLatest data as of February 2011 was used in analysis
Near real-time received through EUMETSATCollocation of GDAS wind vector was done for L1B (slice) and L2A (composite)
Sigma0
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OSCAT Data Flow and Processing Within STAR
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EUM EXGAT
E Server
EUM FTP Data
Server
STAR FTP
Server
NASA/JPL
STAR OWDP
25kmMGDR L2B
NAWIPSAWIPSNWP Buff
L3
Established In Development Development not Started
WebProducts
L1B, L2A, L2B Data
Storing
KNMI JPL
3
ISRO
L1B, and 50km L2A and L2B
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L1B
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Signal & Noise PowerCalculates Signal power
(echo after noise subtraction) and Noise power from the following formulation
Plot as a function of wind speed
Signal is below noise level @ winds < 7.5 m/s in a mean!
s
ssnoise
noise
signals
sssignal
SNRXP
PP
SNR
XP
0
0
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Signal & Noise PowerOSCAT QuikSCAT
Signal Power
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Signal & Noise PowerOSCAT QuikSCAT
Noise PowerLow SNR
~7.5 m/s
Signal Power
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11 % 4 %
89 %96 %
OSCAT QuikSCAT
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Scan Angle Dependence
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L2A
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NEW ISRO 50km L2A
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Slice & Composite bias
SS
SSS
compX
X 0
0
X factor
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L1B → L2A (NOAA)
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OSCAT wind processor
Use QuikSCAT wind processor as a starting point
Process OSCAT data from Level 1B
Grid Sigma0 @ 25 km WVC (L2A)
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ISRO derived WVC index (i,j) from satellite position and velocity vectors(not currently available in routine L1B processing )
Derived WVC index (i,j) by approximation from orbital elements given in L1B attribute parameters, i.e.-Inclination = 98.28 deg-Semi-major axis = 7098.14 km-Eccentricity = 0.00113-Equator crossing longitude (descending node) = varied orbit-by-orbit
NOAA orbit (25 km)ISRO orbit (50 km)
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Composite Sigma0 and STD
SS
SSS
compX
X 0
0
σ0
1
σ0
2
σ0
3
We calculate standard deviation of each Sigma0 from the following formulation
2
00
0 1
Scomp
SS
SS
XX
NSTD
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V-POL Sigma0 Residual BiasFO
RE
LOO
KA
FT LOO
K
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V-POL Sigma0 Residual Bias(Normalized)
FORE LOOK AFT LOOK
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We normalize the residual bias by the standard deviation calculated above:
STDGMFbias comp
norm 0
0
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Residual Bias after Normalization
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Summary and ConclusionsOSCAT data has been flowing to NOAA in near real-time via
EUMETSAT since March 2011OSCAT L1B/L2A investigation shows:
High wind retrievals from OSCAT would be valuableSignal-to-Noise ratio is too low at low wind speeds < ~ 7.5 m/sSigma0 residual biases are significantly high at low wind speedsSigma0 are dependent on antenna scan position and
ascending/descending orbitNOAA is developing enhanced L2A product from ISRO’s L1B
25 km WVC gridL2A product will contain standard deviation of composite Sigma0
Is proving to be useful parameter in definition of objective function normalization during retrieval process
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