ocean vector winds workshop 8-10 feb. 2005 1 c-band scatterometers from ers to ascat and beyond...

Ocean Vector Winds Workshop 8-10 Feb. 2005 1

C-band ScatterometersFrom ERS to ASCAT and Beyond

Ad.Stoffelen@KNMI.nl

Ocean Vector Winds Workshop 8-10 Feb. 2005 2

’ ’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

Ocean Vector Winds Workshop 8-10 Feb. 2005 7

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 scat@knmi.nl

…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

Ocean Vector Winds Workshop 8-10 Feb. 2005 36

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

Ocean Vector Winds Workshop 8-10 Feb. 2005 40

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

Ocean Vector Winds Workshop 8-10 Feb. 2005 51

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

Ocean Vector Winds Workshop 8-10 Feb. 2005 53

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

Ocean Vector Winds Workshop 8-10 Feb. 2005 54

Scatterometers at KNMI;Towards Increased Resolution

Ad.Stoffelen@KNMI.nlJeroen BeysensHans BonekampJos de KloeMarcos PortabellaAnton VerhoefJeroen Verspeek

http://www.knmi.nl/scatterometer

Isabel

Ocean Vector Winds Workshop 8-10 Feb. 2005 55

NWP Impact @ 100 km

Storm near

HIRLAM misses wave;SeaWinds should bebeneficial!

29 10 2002

Ocean Vector Winds Workshop 8-10 Feb. 2005 56

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

Ocean Vector Winds Workshop 8-10 Feb. 2005 57

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: scat@KNMI.nl

Ocean Vector Winds Workshop 8-10 Feb. 2005 58

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

Ocean Vector Winds Workshop 8-10 Feb. 2005 60

http://www.knmi.nl/scatterometer

Ocean Vector Winds Workshop 8-10 Feb. 2005 61

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

Ocean Vector Winds Workshop 8-10 Feb. 2005 70

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