Windhoek - Namibia - Continued
|  | False colour infrared MERIS image acquired on on 19 August 2007 | |
Water for Windhoek
There is a long-standing discussion on a project to provide water to Windhoek and the surrounding cities and settlements from the distant Okavango River.
This river flows from the Angolan Highlands into the Kalahari Depression, where it ends in a huge inner delta. Look up the geographical situation in your atlas.
Does Namibia have access to the river?
And if so, how long must a channel or pipeline be to reach Windhoek?
The MERIS image showing the Okavango Inner Delta in the centre is provided in the file on the right. The part of the river belonging to Namibia starts at coordinate 595,58 (17.3872S, 18.421E = 17-23-14S, 18-25-16E), and extends for some 370 kilometres southeastwards. The pixel size of the MERIS image is 300 m. Display the image, input the pixel size ('Image' – Pixel Size…) and, having filled the 2 fields, go to 'Measure tool' also under 'Image'. Do not forget to change 'Units' to metres.
Download Namibia_data.zip. Using the Mosaic_Namibia_MERIS_20070819_ bands 14, 7 and 5 as red, green and blue combination you can inspect the area in more details. If you have installed Google Earth click to open the file Google Earth MERIS mosaic 20070819RGB_14_7_5.kmz. In the Namibia Geology directory you will find a GIS. Use ArcExplorer to open the NAMIBI...ArcExplorerProject file.
Technical details for the generation of 'Namibia_asar325_meris_PC321'.
The generation of the 'Namibia_asar325_meris_PC321' image is not trivial. But using the LEOWorks software available on this site it is possible to do it.
Download Zip file Namibia_PC-Analysis.zip.
The radar image: 'Namibia_asar_ws_031112_325m_resol'
The optical/infrared false-colour MERIS image: 'Namibia_meris_031215'
The GCP-file (see text):
'Namibia_asar325_meris2.txt'
You need to display both images and then match them perfectly. Finally, you must process them to generate 'optimised' data sets. This means you need to compress the information of 4 bands into 3. All image processing is based on LEOWorks software that can be downloaded here.
After having displayed both images (on the main menu bar press 'File' – Open), use 'Tools' on the main menu bar, then press Registration – Image to Image. On the appearing window, click on the radar (ASAR) image as the maste,r and the MERIS image as the slave. Now you have to look for match points (GCP, Ground Control Points).
Find and click geographically identical points on both images and click 'Add Point'.
You need at least 5 well distributed pairs of points in the master image. Check the RMS value. It should be well below 3. If you fail to find good enough GCPs resulting to a low RMS value, you may use the GCP file we have prepared. To load this GCP file (Namibia_asar325_meris2.txt), press 'Option' on the GCPs Collection window and press 'Restore GCPs from Ascii', look for that file and open it. Now press 'Wrap Image', and a new window, named 'New Image', with the geometrically corrected image, will appear.
The next step is to produce 'optimised bands', the principal components, of both the ASAR and the corrected MERIS image. Split your 'New Image' into the 3 bands. Use 'Image' on the main menu bar, Split to… , [Red Green Blue] – and you will get the 3 bands of the corrected MERIS image as black and white images.
Now press 'Multivariate Analysis' on the main menu bar, and then 'Principal Components Analysis' and in the PCA window select by clicking on the 3 bands (resulting from the 'New Image') and on the radar image (Namibia_asar_031112_321m_resol). Keep the CTRL key pressed in order to select all the required images. Press OK.
The result of the processing will be 4 new windows with Principal Component 1,2,3 and 4. Enhance each of them by using 'Enhance' – Histogram Equalization. Now you can combine Component 1,2 and 3 in a new colour image, using 'Image' – Combine from… [Red Green Blue], and you will get a colour image similar to Namibia_asar325_meris_PC321. Of course you can try any kind of combination of the original (but geometrically adapted) MERIS bands and the radar image.
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