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C-band ScatterometersFrom ERS to ASCAT and Beyond
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’ ’2020 ’ ’1010 ’ ’0000 ’ ’9090
ASCAT-3ASCAT-3
ASCAT-2ASCAT-2
ASCAT-1ASCAT-1
SeaWinds-2SeaWinds-2
SeaWinds-1SeaWinds-1
NSCATNSCAT
ERS-2ERS-2
ERS-1ERS-1
?
RFSCAT ??RFSCAT ??
Continuity of C-band scatterometers?
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Outline
• ERS scatterometer (SCAT)
• Advanced SCAT (ASCAT)
• Satellite Application Facilities (SAF) / Products
• Rotating Fan-beam SCATterometer (RFSCAT)
• Summary and references
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Scatterometers
• Improved forecasts of cyclones and storms (no rain gaps)
Isaksen & Stoffelen, 2000
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Local revived real-time ERS scatterometer service
ERS Monday 6 Sep 04
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http://www.knmi.nl/scatterometer
ERS Monday 6 Sep 04
Mouse click
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http://www.knmi.nl/scatterometer
ERS Monday 6 Sep 04
Mouse click
Remnence of Frances
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Fast developing
low over the ocean
missed by HiRLAM
ESA press release
“Nowcasting”
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The METOP Instrument Payload
IASI
HIRS-4
AVHRR-3
AMSU-A1
AMSU-A2MHS
GOME-2GRAS
ASCAT
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The ASCAT Mission
• Primary objective: To provide global ocean wind vector measurements operationally. Main application: assimilation in Numerical Weather Prediction models
• Additional objectives supported: – Retrieval of sea ice boundaries, concentration and
type– Retrieval of land surface parameters: snow cover
and soil moisture– Nowcasting– Probably stress product
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Heritage from ERS scatterometers and new ASCAT features
45o
135o
90o
Beam geometry
C-BandVV polarisation
Spatial averagingin overlapping cells(one o ‘triplet’ per WVC)
50 km resolution; one WVC every 25 km (19 across swath)
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Heritage from ERS scatterometers and new ASCAT features
45o
135o
90o
Beam geometry
C-BandVV polarisation
Spatial averagingin overlapping cells(one o ‘triplet’ per node)
Additional product at ~25 km resolution, every 12.5 km(41 nodes per swath)
Improved instrument design and on-board processing concept
45o
135o
90o
Increased time and swath coverage
550 km
Higher incidence angle range
i.a.: 25o - 65o
50 km resolution; one WVC every 25 km (19 across swath)
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The spatial averaging: one and consecutive 50 km resolution WVCs
100 km
50 km50 km 50 km
25 km
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ASCAT Products
• Level 1B (EUMETSAT)– 50 km resolution o triplets with a 25 km WVC
spacing– ~25 km resolution o triplets with a 12.5 km WVC
spacing– Full-resolution o values for the three beams on each
swath (research product)
• Level 2 (Ocean and Sea Ice SAF)– 50 km resolution wind vectors with a 25 km WVC
spacing– ~25 km resolution wind vectors with a 12.5 km WVC
spacing
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ASCAT products disseminated to usersProduct Contents Format Dissemination Timeliness
Source
Level 0 ASCAT EPS HRPT NRT MetOpsource packets format L-band real time platform
Level 1B o triplets EPS NRT terminals 2h 15 minEUMETSAT
50 and ~25km BUFR EuMetCast >15 minresolution
Level 2 winds + o BUFR RMDCN, 2 h 30 min OSI SAFtriplets internet and >20 min information EuMetCast over ocean
ADP data processor s/w - - OSI SAF
NRT terminals are being substituted by increased EuMetCast capability
Note that o data is available in both L1B and Level 2 products
Archive data is available from EUMETSAT from 2007 including full resolution
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The SAF concept
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Satellite Application Facilities
Scatterometer sea surface wind R&D– Quality control, rain and ice screening – Spatial averaging (100 km 25 km)– Inversion: Computation of wind solutions and associated
probabilities from measurement information– Determination of information content; Observation operator
Ambiguity removal (spatial filter to determine unique field)– Active monitoring and control (of instrument and processing)– Web site (visualisation) and product distribution
ERS and QuikScat product enhancement Preparation for ASCAT wind production (METOP; 2006)
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Flow around rain cells
12 July 2004 1:30Z
Mesoscale flow
Rain Contamination ?
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C- and Ku-band synergy
QuikScat 5 GMT
ERS-2 21:30 GMT
September 2004
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– CMOD5 provides cone– Ice model (ice age a)– WVC dependence through
incidence angle
Ice Line & Wind Cone
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OverlapCone andLine
Mixed points
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Along-the-ice parameter
indicates ice type
•Red/yellow: multi-year ice
•Green/blue: first-year ice
0<-10 >10a
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Blended Operational Ocean/Ice Products
• DNMI:OSI SAF at high-lat. – Under Météo France
contract to with DNMI (N), DMI (DK) and SMHI (SWE).
• 3 Std. OSI SAF Products– Ice concentration (%) – Ice edge: probability of
ice coverage – Ice type: probability of
multi-year/ first-year
• Sensors– SSM/I + ERS Scatt +
AVHRR - blended ice concentration
– QSCAT vector wind (dealiased)
• Blended Products (see right)
– Ice Coverage/Type (as above) + Wind (HIRLAM + QSCAT)
– Used in “met. workstation” by met. Institutes in Eumetsat
See: OSI-SAF web page
Courtesy Lars-Anders Breivik - DNMI
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climexp.knmi.nl
• ERS and NCEP re-analysis stresses deviate substantially • Few gaps in dynamic areas (unbiased)
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Rotating Fan Beam Scatterometer (RFSCAT)
– Coverage– Resolution– Quality
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RFSCAT options
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Comparison
• Figure of Merit (FoM)– Complementary
quality in a WVC– User
requirement– Errors– Wind ambiguity
– Coverage not yet included
– H-pol useful
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RFSCATPreliminary conclusions
• A C-band VV-pol RFSCAT does not gain much performance on ASCAT
• An added HH-pol channel provides more information around the satellite ground track.
• With a polarimetric RFSCAT at moderate cost for RF power a significant gain in wind retrieval may be achieved, but capitalizing this in spatial resolution remains to be seen
• Wind variability within a WVC limits performance at high SNR
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C-band scatterometers
• Continuity may be possible ERS-1 -> ERS-2 -> ASCAT-1,2,3 -> ?
• Proven useful for dynamic weather forecasts
• Few gaps in dynamic areas (no climatological bias)
• Combination of H-pol and V-pol would improve performance
• Wind, land, ice, nowcasting
• Ongoing improvement of GMF, its inversion, QC, data assimilation, monitoring
• Near coastal application remains to be investigated (see SAR)
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For more info...
…on the web
• EUMETSAT web page, www.eumetsat.de
• ESA MetOp web page, www.esa.int/export/esaME/
• KNMI OSI SAF, page www.knmi.nl/scatterometer or mail [email protected]
…publications
• ESA bulletin, Special Issue on MetOp (nr. 102, May 2000)
• J. Figa-Saldaña, J.J.W.Wilson, E.Attema, R.Gelsthorpe, M.R.Drinkwater and A.Stoffelen, The Advanced scatterometer (ASCAT) on the meteorological operational (MetOp) platform: A follow on for European wind scatterometers, Can. J. Remote Sensing, Vol.28, No.3, pp. 404 - 412, 2002
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Scatterometer
• Verbeterde voorspelling van cyclonen
Isaksen & Stoffelen, 2000
IsabelGeen ERS Scatterometer Wel ERS
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NWP impact@100-km
At DNMI and DMI:
About 10% gain in forecast length for Autumn 2001
More neutral in January 2002
Gain
© Frank Tveter, DNMI
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N
ioNi
osi
omi
KpNMLE
1
2
)(
1
space
zz o 625.0
constant
Calibration method:
Look for the transf.
oa constant
N
isimi zz
NMLE
1
21
)()|(
)|(os
os
om
om
os
PP
P
noise cone shape
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Problem: CMOD5 cone too wide
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Ifremer ice map Distance to ice line
0 >51 2 3 4dice
ERS-2, Jan.3-Jan.9, 2000
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3. Wind Retrieval
• Bayesian approach:
• MLE inversion:
• constant
• Is MLE inversion still valid?
)()|()|( os
os
om
om
os PPP
N
ioNi
osi
omi
KpNMLE
1
2
)(
1
)( osP
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ERS Scatterometer SeaWinds
• In general, wind retrieval of reasonable quality
• However, wind direction distributions present unrealistic peaks & gaps
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WVC x
x
x
x
x
x
x
x
1
865
3
24
7
FOV
uFOV = uFOV + u
vFOV = vFOV + vu, v N(0,0.75)
Generally, <GMF(uFOV, vFOV)> <GMF(uWVC, vWVC)>
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EUMETSAT Polar System: an Integrated European Effort
Areas of involvement
• ESA: Space Segment (MetOp platforms and ASCAT, GRAS, GOME instruments)
• EUMETSAT:Space Segment, Ground Segment, Launcher services, EPS Operations – EUMETSAT Member States: Satellite
Applications Facilities (SAFs)
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EPS operational mission schedule
Operational mission planned for 14 years of operations
• Three MetOp platforms launched in: – October 2005– 2010– 2014
• Commissioning planned to last 6 months for each of the three satellites
• Overlaps between missions foreseen during the Commissioning periods
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ASCAT Instrument Design/ on-board processing
Long pulse with LFM (‘chirp’)
• After de-chirping, the resulting signal is spectrally analysed and detected. In the power spectrum, frequency maps into slant range.
• The above processing is in effect a pulse compression, which provides range resolution.
• Radiometric and geometric performance specification in line with ERS scatterometers
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ASCAT calibration
• Internal calibration– compensates for transmitter power and receiver gain
variations. Automatic mechanism applied during the ground processing.
• External calibration– Objective is that o from a target is accurately measured
(absolute calibration) over all incidence angles and between beams (relative calibration), during the whole mission (calibration stability).
– Baseline is absolute and relative calibration with 3 transponders and calibration stability monitoring over natural targets (rainforest, ice and ocean).
– Additionally, cross-calibration with the ERS scatterometers will be assessed.
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The spatial averaging: objectives and method
• Objective: to achieve radiometric resolution or Kp (standard noise of the measurement)
• Hamming window of two different sizes at two different spatial grids:– 50 km resolution at 25 km node spacing– ~25 km resolution at 12.5 m node spacing
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Archived ASCAT products available to users
Product Contents Format Source“Timeliness”
Level 1B o triplets EPS and UMARF 8-9 h
at 50 and 25-30 km HDF formats resolution
Level 1B o values EPS and UMARF 8-9 h
Full resolution before spatial HDF formats averaging
Level 2 winds + BUFR and UMARF 8-9 hessential o HDF formatsinformation over ocean
UMARF is the EUMETSAT Unified Meteorological Archive and Retrieval Facility
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Summary
• ASCAT mission: Integrated European effort: (3) scatterometers, 14 years of operations, planned for launch aboard MetOp in 2005
• Objectives: operational retrieval of ocean winds, sea ice and land surface parameters
• Heritage from ERS scatterometers with improved coverage, performance and an additional high resolution product
• Data processing and distribution: joint effort between EUMETSAT central facility and the Ocean and Sea Ice SAF
• Products from ASCAT provide a continuation of the already long time series of ERS C-band backscatter measurements
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MetOp Operational orbit
• Assumption– EPS is the European contribution to the polar-orbiting
operational global observing system, where Europe (EUMETSAT) will cover the morning orbit and the USA (NOAA) will cover the afternoon orbit
• Main characteristics of the orbit– Sun-synchronous– MLST at descending node is 9:30– Orbit repeat cycle of 29 days– Minimum orbit height of 822 km– Launch first METOP (2!) end 2005 still, then 2010 &
2014
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Scatterometer Data Processor
Observations Inversion Ambiguity Removal
Wind Field
OUTPUTOcean Surface Radar Backscatter Observations
Inversion Ambiguity Removal
Quality Control
Pre- Process
Wind Field
INPUTOUTPUT
Quality Monitor
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Scatterometers at KNMI;Towards Increased Resolution
[email protected] BeysensHans BonekampJos de KloeMarcos PortabellaAnton VerhoefJeroen Verspeek
http://www.knmi.nl/scatterometer
Isabel
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NWP Impact @ 100 km
Storm near
HIRLAM misses wave;SeaWinds should bebeneficial!
29 10 2002
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Way forward
Scatterometer winds contain mesoscale detail not captured by NWP fields
This information is useful for nowcasting
MSS is an effective way of controling the noise
Spatial analysis in progress
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Further ReferencesFurther ReferencesFor scatterometer-related papers, documentation, and
wind products of the SAFs please refer to
http://www.knmi.nl/scatterometer
We look forward to sharing
- Our scatterometer processing software
- Our ERS and QuikScat products
- Our new wind stress products
- Our experience
We fund visiting scientists
E-mail: [email protected]
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Timeliness of QuikScat files
-50 0 50 100 150 200 250
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Timeliness of QuikScat files
60% loss in KNMI HiRLAM
assimilation cycle
-50 0 50 100 150 200 250
UsedLost
Update cycle implemented
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http://www.knmi.nl/scatterometer
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Satellite Application Facilities (SAF)Scatterometer participation at KNMI
• NWP SAF– Scatterometer Wind Processing Software and Observation Operator for
NWP Data Assimilation: SeaWinds Wind Processor version 1
• Ocean and Sea Ice SAF (OSI SAF)– Scatterometer Wind Production, Monitoring and Web Visualisation:
100-km NRT SeaWinds product on FTP site; ASCAT L2 in 2006
• Climate Monitoring SAF (CM SAF)– 10-year ERS Scatterometer Wind Stress Data Base (1991-2000):
available this year (based on CMOD5)
Effective international collaboration is essential to try and exploit the many available satellite data
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NWP Impact @ 100 km
Storm near
HIRLAM misses wave;SeaWinds should bebeneficial!
29 10 2002
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Spatial resolution
• Scatterometers provide information on scales of ~50 km
• NWP models have great difficulty to assimilate detailed
information (< 200 km)
Scatterometer winds contain mesoscale detail not captured by NWP fields, due to poor GOS aloft