Exercise 2 - Annapurna Circuit - Continued
|  | Treeless mountains around Kagbeni on the Annapurna Circuit | |
Annapurna Circuit Profile
This exercise requires the LEOWorks software. If you have not downloaded the programme, do so now.
If you have not downloaded the satellite images of the Annapurna region either, go to the top of the section and download them now.
An additional dataset required for the following exercise can be downloaded as a ZIP file (see below). This is a 16 bit digital elevation model (DEM) of the Annapurna Conservation Area. The value of each pixel consequently corresponds to the height of that geographical point in metres.
Download the elevation model (subuint_annapurna.zip).
It is therefore possible to read out the heights of specific geographical features to update the attributes of the GIS files. We are going to collect the elevation data for the cities and lodges along the Annapurna Circuit, so as to draw an elevation profile of the trek. A profile of this kind is very useful when planning daily travel distances. 10 kilometres a day might not sound like a lot, but if you know that you have to climb 2,500 m in altitude with a heavy backpack, you certainly will look at the distance in a different way.
The DEM we are using was created using radar data from the Shuttle Radar Topography Mission (SRTM), and has a ground resolution of 100 m per pixel.
Unfortunately it is not so easy to handle a 16 bit file in LEOWorks. You must therefore follow the steps described below very carefully.
Open the LEOWorks programme. Open the elevation model subuint_annapurna.tif. The image looks kind of cracked. To enhance the picture, select Enhance>Interactive Stretching. Do not click Apply. The image will already have changed appearance, but if you click on Apply, the elevation information will be lost. So set the Interactive Stretching menu aside and leave it as is.
When you look at the image, you will find large and small black zones. These zones are undefined because the radar sensor was not able to collect sufficient data to calculate the elevation in these areas. A radar is an instrument that views from the side. Just as the Sun cannot illuminate areas that are hidden by mountains, radar sensors cannot obtain information regarding these areas.
Even so, the image is good enough to work with. The 4 elevation data for lodges which are missing in the model have already been prepared and stored in the database for the GIS layer City Lodge.
To open the GIS layers City Lodge and Annapurna Circuit, choose GIS>File>Open theme, and select the first layer City Lodge. To load the data, an Input Projection has to be defined.
The specifications are:
- Transformation Method: UTM
- Datum Name: WGS 84
- UTM Zone: 44
- UTM Hemisphere: North
Now choose Edit>Properties and select Cross (X) for Symbol.
Open the Annapurna Circuit layer in the same way, but leave the Properties unchanged.
| | | Elevation profile for the Annapurna Circuit |
The next step is to collect the elevation data. To do this select City Lodge in the GIS Toll for image window and choose Tools>Information. A pop-up menu Theme Information opens. Click the first point. The attribute and value appears in the window and the cross in the map changes to a plus. That is the point to which the attribute is assigned.
Place the crosshair on top of the cross and read the elevation in the status line at the lower left of the image frame. Write down the name and the elevation and repeat these steps for all points along the route.
When you have collected all the information, close the window Theme Information and open Edit>Properties. Type the elevation data acquired for the highlighted city or lodge into the column Height. When the table is complete, click OK and save the theme File>Save theme.
The elevation data for the cities, lodges and base camp(s) are now saved in the database of the GIS file City Lodge, like the Heights in the layer Peak.
To draw the elevation profile for the Annapurna Circuit, download the ready-made PDF file.
Simply print the file and transfer the heights of the locations onto paper. Connect the elevation points to obtain the profile.
The easiest way to read out the heights is to open the Properties for the layer City Lodge. The table of attributes provides the name and the height of each location.
Compare your manually prepared elevation profile with the ready-made one (pdf). What is the main difference between these profiles? What is the reason for these differences?
Consider the Thorung La pass in particular. Why is it missing in the manually drawn profile?
How would it be possible to manually create an elevation profile showing a similar data density? Try it for a small section of the route, for example between Kagbeni and Tukuche.
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