Procedure for downloading a 90-meter SRTM Digital Elevation Model from the EBM server at NCEAS

Author: Matthew Perry (perrygeo@gmail.com)

Date: 04/13/2006

Original Data and Metadata: http://srtm.csi.cgiar.org/

1.      Go to http://ebm.nceas.ucsb.edu/mapping/srtm.php4

2.      Use the zoom tools to locate your area of interest

3.      Click the Download SRTM button in the upper-right

4.      Your browser will save the data to your disk (probably to your Desktop) as a file named ‘mapserv’. Once the download completes, rename the file to something like ‘srtm.img’. The prefix can be anything you’d like but the file extension should always be ‘.img’

5.      Open ArcMap and add the newly created .img file to your map

6.      Show the ArcToolbox window and go to Spatial Analysis Tools > Conditional > Set Null

7.      Open the Set Null Tool and enter the downloaded img file for the first two parameters, the desired output grid for the third parameter and “Value = -32768” for the fourth. This step removes null values for non-land areas of the SRTM data.

8.   The output raster should be added to you display and is now ready to go. The projection of the SRTM data is Geographic with a WGS84 datum so you may need to reproject it to work with other datasets.

Accessing directly through WCS request

http://ebm.nceas.ucsb.edu/cgi-bin/mapserv?map=/maps/srtm_90m.map&Version=1.0.0&request=GetCoverage&Coverage=srtm&service=WCS&CRS=EPSG:4326&Format=image/hfaint16&resx=0.0008333333333&resy=0.0008333333333&BBOX=-120,34,-119,35

• image/geotiffint16 : 16-bit integer geotiff
• image/aaigridint16 : Integer ascii raster
• image/hfaint16 : 16-bit ERDAS img (HFA)
  
• image/jp2kint16 : 16 bit integer jpeg2000
• image/hdfint16 : 16 bit HDF
  
• image/pngint16 : 16-bit PNG