Bringing satellite winds to hub-height

Bringing satellite winds to hub-heightMerete Badger, DTU Wind Energy, Denmark

Rolv Erlend Bredesen, Erik BergeKjeller Vindteknikk, Norway

Alfredo Peña, Andrea Hahmann, Jake Badger, Ioanna Karagali, Charlotte Hasager, Torben MikkelsenDTU Wind Energy, Denmark

DTU Wind Energy, Technical University of Denmark

Ocean wind fields from satellites

2 04/19/2023

Scatterometer Synthetic Aperture Radar (SAR)

Retrieved parameters Wind speed and direction Wind speed

Spatial resolution 0.25°lat/lon 500 m

Spatial coverage Global Selected areas

Coastal mask Up to 70 km from coastline None

Temporal resolution Twice daily Variable – less than one per day

Temporal coverage Systematically since 1991 ScanSAR since 1995

Current sensors ASCAT, OSCAT, HY2A, MetOp-B

Envisat ASAR, Radarsat-1/2

Rain sensitivity High – rain flags provided Low


Level of detail for scatterometer and SAR winds

Presentation name3 21 Jan 2012QuikScat mean wind speed Envisat ASAR mean wind speed


From radar backscatter to wind

Presentation name4 21 Jan 2012

A geophysical model function is applied to retrieve 10-meter ocean winds from radar backscatter.

DTU Wind Energy, Technical University of Denmark Presentation name5 21 Jan 2012

Application 1:Wind resource mapping from SAR wind fields- and model validation


Application 2:Wind farm wake analyses using SAR wind fields - and wake model validation


Wind speed from ERS-2 SAR,February 25, 2003

From: Christiansen, M. B. & Hasager, C. B. 2005, Wake effects of large offshore wind farms identified from satellite SAR. Remote Sensing of Environment, 98, 251-268


Challenges for the application of SAR wind fields in offshore wind energy

Challenge 1: Dealing with a limited number of samples

See: Badger et al. 2010, Wind class sampling of satellite SAR imagery for offshore wind resource mapping. J. Appl. Meteor. Climat., 49, 2474-2491.

Challenge 2: Bringing satellite winds from the 10-m vertical level to the hub-height of modern wind turbines

- the topic of this presentation



Recent advances - which make the lifting of SAR wind fields possible

• A validated description of vertical wind profiles at high levels is available

(Peña, A. et al. 2008, Measurements and Modelling of the Wind Speed Profile in the Marine Atmospheric Boundary Layer, Bound.-Layer Meteor., 129, pp. 479-495)

• Wind retrieval algorithms can produce Equivalent Neutral Winds (ENW)

(Hersbach, H. 2010, Comparison of C-band Scatterometer CMOD5.N Equivalent

Neutral Winds with ECMWF, J. Atmos. Oceanic Technol., 27, pp. 721-736)

• Satellite SAR imagery is available in larger quantities

(500-1,000 overlapping scenes over sites in the European Seas)

• Mesoscale modeling has been performed for significant areas and time periods

• Offshore measurements are available for validation (masts and LiDAR)



Bringing satellite winds to hub-height (100 m)

• Friction velocity, u* from the satellite ENW:

,

• Obukhov length, L

- using WRF parameters T2 and HFX:

LWRF/SAR > 0: stable

LWRF/SAR ≤ 0: unstable


g

uz SAR

c0

2

WRF

WRFSARSARWRF HFXg

T2uL

3

/

0

SARSAR10 z

uu

10ln


Bringing satellite winds to hub-height (100 m)

• Stability function, ψ(z/L):

LWRF/SAR > 0 :

LWRF/SAR ≤ 0 : ,

• Wind speed at 100 m, u100

- using WRF parameters T2, HFX, PBLH:

LWRF/SAR > 0 :

LWRF/SAR ≤ 0 :


33

12arctan3

3

1ln2

3 2

/

xxx

SARWRFL

z

3/1

/

121

SARWRFL

zx

SARWRFL

z L

z

SARWRF /)(

7.4/

PBLHz

uu

SARWRFL0

SARSAR100 2

1001

100ln

/

100

SARWRFL0

SARSAR100 z

uu

/

100

100ln


Envisat ASAR data collection


Data archive at DTU:

>8,000 ASAR WSM scenes

Mainly for 2006-2011

Additional scenes can be ordered from ESA (2002- ) – now free of charge

Daily download of new scenes covering the NORSEWIND domain:


100-m winds at Fino-1



100-m Weibull fit at Fino-1



Spatial wind variability over the North Sea



Sampling effects over the North Sea



Special situation: Low boundary-layer height

• The applied wind profile equations are valid within the atmospheric boundary-layer

• Data are discarded when the boundary-layer height is <50 m

• Up to 4% of the WRF samples are discarded over the North Sea over a year

• None of the 80 SAR scenes, and concurrent WRF samples, are discarded



Conclusions

• Satellite SAR data lifted to 100 m under-estimate the wind speed at Fino-1

• Concurrent WRF simulations also under-estimate the 100-m wind speed at Fino-1

• SAR-WRF agreement is generally good over the North Sea with the largest differences near the coast of Germany

• The number of SAR samples (80) is insufficient to describe the mean wind climate accurately

• Work is in progress to improve the accuracy of lifted satellite wind fields

• Satellite observations represent a valuable source of information for offshore wind energy applications (e.g. wind resource mapping, wind farm wake analyses)



Acknowledgements

Satellite data:

The European Space Agency (ESA)

Remote Sensing Systems (RSS)

SAR wind field retrieval:

Collecte Localisation Satellites (CLS)

The Johns Hopkins University, Applied Physics Laboratory (JHU/APL)

Fino-1 and Fino-2 mast data:

Bundesministerium für Umwelt (BMU), Projektträger Juelich (PTJ), Deutsches Windenergie Institut (DEWI)

Funding:

EU-NORSEWInD (TREN-FP7EN-21908)

18 21 Jan 2012Presentation name

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Bringing satellite winds to hub-height