Wr4-2 Srtm Maps

7/28/2019 Wr4-2 Srtm Maps

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Niels G. Mortensen & the WAsP team


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Outline

Introduction to SRTM mission and

How to get SRTM data

Conversion to WAsP maps

SRTM ma s are not et com lete

Pitfalls

Be careful!

WAsP and raster maps

Jan 2012Course 457002 DTU Wind Energy


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Shuttle Radar Topography Mission

Space Shuttle February 2000

Resolution ~ 2525 m2

80% of the Earths land mass

9 terabytes of raw data

r po n e eva ons or every

1 arc-sec (~30 m) for USA

3 arc-sec (~90 m) outside

Vertical accuracy 5-10 m (z)

Unedited and finished data (v 2.1)

Digital Surface Model rather than

Digital Elevation Model

For more information, visithttp://www2.jpl.nasa.gov/srtm/



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SRTM coverage map


Colour indicates number of passes by space shuttle Endeavour


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Hand-digitised and SRTM maps

3110

3110

3100

Gulf of Suez

3100

Gulf of Suez

3090

hing[km]

N

NW

3090

hing[km]

N

NW

3080N

ort

Gulf of El-Zayt

3080N

ort

Gulf of El-Zayt

3070 SW

Ras El-Behar 3070 SW

Ras El-Behar


Easting [km] Easting [km]

Hand-digitised SRTM map


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Example from Portugal

Hand-digitised map SRTM map Wind

StationElevation

[m a.s.l.]

RIX

[%]

Elevation

[m a.s.l.]

RIX

[%]

U10

[m/s]

Port 06 933 25 930 28 4.49

Port 07 982 29 980 33 5.16

Port 08 1047 17 1040 18 6.06

Port 09 1082 9 1070 10 5.84

Port 10 1012 9 1010 11 5.56



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SRTM and reference maps

Referencezis

by IGeoE

Unedited SRTMprocessed likedescribed above

Spacing of gridpoints is 100 m

Difference iscalculated as =z zref foreach grid pointand coloured, see

.

= 2.5 m

= 5.7 m


-


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Map characteristics

Hand-digitised from 1:25,000 maps

50- and 10-m height contours

Contoured from SRTM data (Surfer)

10-m height contours all over


Spot elevations Spot elevation (mast only) added


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Comparison of WAsP cross-predictions

10

8

9

ps)[ms-1] Up @ 10, 50, 100 m

Y= 0.99 X+ 0.08

7

eed(SRTM

m

5

6

ictedwindsp

3

4Pre


Predicted wind speed (handmade maps) [ms-1]


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Three sample 20-MW wind farms

Turbine type Gamesa G47 Nordex N62 Enercon E66

Rated power 30660 kW 161300 kW 111800 kW

Hub height 50 m a.g.l. 69 m a.g.l. 67 m a.g.l.

Total net AEP 57.7 GWh 56.8 GWh 58.3 GWh

Ran e [GWh] 1.77-2.17 3.10-3.99 5.11-5.43

SRTM maps* = -0.9% = -0.4% = -1.7%

Range [GWh] 1.76-2.18 3.19-4.07 5.17-5.44

*Details onl addedaround themet. station not the turbine sites!



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Transformation to WAsP maps

SRTM grid coordinates are non-projected (latitude, longitude).

or zon a re erence sys em a um s

Vertical reference system is the EGM96 geoid

Transformation of coordinates to metric system

Construction of height contours (vector) from grid data (raster)

Map examples shown above have used

Geo-projection utility or Map editor for coordinate transformation

Surfer 9 (Golden Software) for contouring (see www.wasp.dk)

Other software exist to view and transform SRTM data, such as

Global Mapper 11 (commercial, Global Mapper Software LLC)

-



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Construction of height contours from grid data



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Download SRTM data from web site

http://dds.cr.usgs.gov/srtm/version2_1/ File name-

left (LL) corner of11 degree tile

HGT format iss m ar o eGTOPO30 DEMformat which is

supported by e.g.Surfer

Coastline dataexist as well onweb site (SWBD)

Some void-filleddata sets exist aswell, e.g. CGIAR-CSI 4



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SRTM data conversion be careful!

The result is a WAsP ASCII map that can be used for WAsP analysis.

If spikes and voids represent large problems, the more comprehensivemethod described at www.wasp.dk could be used.

Do remember...

that the SRTM elevation data have not been tested in all parts of the.

that when you carry out a WAsP project, you are in charge andresponsible for evaluating the WAsP inputs and the results includingthe availability and quality of SRTM data.

More data sets are coming

ASTER Global Digital Elevation Model



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ASTER Global Digital Elevation Model (GDEM)

Earths land surface between 83N and 83S (99%)


11 degree tiles in GEOTIFF format, 1 arc-sec resolution (~ 30 m)

Documents

Wr4-2 Srtm Maps