Kathmandu - Now and then with optical images - Urban detection
|  | False-colour image (4,2,1) of Kathmandu in 2001, 30 m/pixel | |
The City
Kathmandu is the capital of Nepal. It is a fast-growing city and has changed from a contemplative town with small, quirky alleys to a bustling metropolis accommodating nearly 1,100,000 inhabitants. Kathmandu was founded in the 8th century. Since 1769, when the Kingdom of Nepal was established by the Schah dynasty, it has been the capital and the royal residence of Nepal. The city is situated in the Kathmandu Valley, more than 1 300 m above sea level. The whole region was declared part of the world cultural heritage by UNESCO in 1979, due to the presence of more than 7 000 temples and other shrines in Kathmandu and the surrounding valley.
The growth of the city is clearly visible in the sequence of historic and more recent satellite images which we are going to produce in the following exercise. False-colour images are qualified to detect urban areas. Strong reflection of chlorophyll in the near infrared channel leads to a reddish coloured vegetation. The urban areas are displayed in a dark blue colour range. The extension of developed areas and the borderline vegetation are easily visible.
Open the LEOWorks programme. If you have not downloaded the images of Kathmandu yet, do so now (see right).
Choose File>Open. A dialogue box will pop up. Choose the folder
Kathmandu and select the first image
Kathmandu_Landsat_2001_Band_1.tif. Open
Kathmandu_Landsat_2001_Band_2.tif and
Kathmandu_Landsat_2001_Band_4.tif as well.
Choose Image>Combine from...>Red Green Blue. A pop-up menu will open.
Select image Kathmandu_Landsat_2001_Band_4.tif for Red,
Kathmandu_Landsat_2001_Band_2.tif for Green, and
Kathmandu_Landsat_2001_Band_1.tif for Blue, and click OK.
Improve the raw data by choosing Enhance>Interactive Stretching. A histogram will appear. Shift the left (blue) bar in the Input Histogram to the left start point of the Input Histogram. Then shift the right (red) bar to the right start point of the Input Histogram and click Apply. Note the changes in the combined image. Convert the other two images in the same way.
Note: The band combination for the Landsat MSS data is slightly different, due to the different sensor onboard the MSS. Use bands 6,5,4 to combine the RGB false-colour image.
How far you have to shift the bars for each band depends on your perception of colour and the colour adjustment of your screen.
Follow the above instructions to produce two other false-colour images, one using the 1989 Landsat TM data and the other using the 1976 Landsat MSS data. Then print the images.
The scale of the images (when printed without further print options) is 1 : 75.843. That means that 1 cm equals 758 m.
The goal of this exercise is to analyse the urban development of Kathmandu and its seasonal changes.
Study the different colours in the images. Allocate the colours to the four main classes of land cover: urban area, forest, arable land and bare soil.
Compare and describe the three images in terms of the vegetation, which is shown in reddish colours, and find out the differences and the similarities. Explain the reasons for both of these.
Take a sheet of tracing paper and cover the 1976 image with it. Mark the corners of the image with cross-bars and draw the city limits of Kathmandu in 1976. Put the paper on top of the 1989 image using the cross-bars. Draw the city limits of Kathmandu in 1989. Repeat the same steps to draw the city limits of Kathmandu in 2001. Colour the areas marked with different colours and describe the expansion of the city.
To calculate the approximate surface changes, place the tracing paper on top of a sheet of scale paper and count the squares in each polygon, taking into account that one square mm equals 0.0057 square km.
Based on the three images and your analysis of the urban expansion, discuss the possibilities and limits of further expansion of the city in the Kathmandu Valley.
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