Continued - Cairo - Then and Now
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Measuring
See: Surface Calculating - Cairo, in exercise 1:
Exercises using Landsat data
In the 'Orientation' exercise you tried to guess the size of the circumference of the city of Cairo in 1874.
Now we can measure the size, because the image Cairo_1874_REF.tif now has the same resolution as the Landsat images: 1 pixel = 30 metres.
Choose File>Open. A dialogue box will pop up. Choose the folder Cairo and select image Cairo_1874_REF.tif.
Choose Image>Pixel Size and set the value of X and Y to 30.
Choose Image>Measure Tool and choose Units>Metres.
Draw a polygon around the red built-up area of the 1874 city of Cairo. Start at the south side by clicking on the right mouse button. Draw the polygon along the city limits and close it by using the left mouse button.
All information is shown in the dialogue box: the length of every single vector, the length of the polygon and the surface area.
Convert the m² into km². Compare the measured circumference with that of your previous estimate.
GIS
ArcExplorer is a lightweight GIS data viewer developed by ESRI. This freely available software offers an easy way to perform basic GIS functions. ArcExplorer is used for a variety of display, query, and data retrieval applications, and supports a wide variety of standard data sources. It can be used on its own with local data sets, or as a client to Internet data and map server.
You can download ArcExplorer by clicking on the link on the right.
As you know from the previous exercises you did, Cairo is a city of change and expansion. The object of this exercise is to print an appealing file displaying the huge growth of the city of Cairo.
Choose File>Open form LEOWorks toolbar. A dialog box will pop up. Choose the folder Cairo and select image Cairo_1874_REF.tif.
Zoom into the image until it fills the screen. Then choose GIS from the toolbar.
A pop-up menu opens. Choose File>New Theme, name the theme '1874' and select Polygon. To start drawing select Edit>Start Edit.
Draw a polygon around the 1874 red built-up area of the city of Cairo. Start at the south side by clicking on the right mouse button.
Draw the polygon along the city limits and close it by using the left mouse button.
To stop drawing, select Edit>Stop Edit. Save the file as '1874' in the folder 'Cairo'. Exit the LEOWorks programme.
Open the ArcExplorer programme. If you have not downloaded the programme yet, do so now.
Choose Theme>Add Theme.... Choose the folder 'Cairo' and select image Cairo_Landsat_2000_Band_321.tif. Now select the vector-file 1874.shp produced in LEOWorks.
Both files appear in the ArcExplorer Local box. Activate the boxes to the left of the filenames.
For good print presentation we need to change the character of the vector file. Double-click on the file '1874' in the Local box. Choose Cross fill for Style and change the colour to red.
Now the image is good enough to show your friends and family! You can now print the image and take it home.
Landsat 1982
Cairo is a fast growing city and therefore it needs new subsoils for residential areas and an enlarged street network. Satellite images act as planning and control instruments and document the changes.
What changes can be identified by comparing Landsat data from 1982 and 2000? Did the city grow and enlarge its infrastructure over that period?
Open the LEOWorks programme. If you have not downloaded the images of Cairo yet, do so now.
Choose File>Open. A dialogue box will pop up. Choose the folder Cairo and select the image Cairo_Landsat_1982_Band_1.tif. Open image Cairo_Landsat_1982_Band_2.tif and Cairo_Landsat_1982_Band_3.tif, too.
Choose Image>Combine from...>Red Green Blue. A pop-up menu will open. Select image Cairo_Landsat_1982_Band_3.tif for Red, Cairo_Landsat_1982_Band_2.tif for Green, and Cairo_Landsat_1982_Band_1.tif for Blue, and click OK.
The new image is the true-colour image produced from the 3 visible light channels. But it is not in true colours yet, because it is unimproved raw data. Select (activate) the first image cairo_landsat_1.tif and choose Enhance>Interactive Stretching. A histogram will appear. Shift the left blue bar in the Input Histogram to the left initial point of the histogram. Then shift the right red bar to the right initial point of the Input Histogram and click Apply. Note the changes in the combined image. Convert the other two images in the same way.
The image shows Cairo in the year 1982. For a comparison of the urban development, open the image Cairo_Landsat_2000_Band_321.tif. Print both images in colour.
Take the print-out of Cairo in 1982 and draw in the new features on the image of Cairo in the year 2000. Use different colours to separate the road network, the city spread, the bridges and so on.
Compare your drawing with those of your classmates.
Describe the growth of Cairo over the past 18 years and compare the number of new features and the dynamics of the changes with those in your hometown.
ERS
ERS radar images are composed of 3 data sets/images acquired on 3 different dates. Each greyscale image is displayed in a different colour (red, green or blue) resulting in a full colour image due to changes that may have occurred on the ground between acquisitions (no change would result in a black and white image).
A radar is an active system which transmits microwave pulses (wavelength 5.6 cm) and receives the echo reflected from the ground. Radar images do not show any information related to the colour of the target surface or how it is illuminated. Instead, it shows information related to surface texture.
As vegetation cover grows, the ground surface acquires a rougher texture and hence appears brighter in a sequence of images. Woods are rather bright, and buildings are the brightest objects in an image. Water surfaces are often colourful, because their texture is rarely consistent due to changing wind conditions.
The multitemporal radar image of Cairo, Cairo_ERS_SAR.tif, is produced by using data from 1992, 1997 and 2002. 2002 is used for the red channel, 1997 for the green channel, and 1992 for the blue channel.
Which of the previously identified new features of Cairo are visible in the ERS image?
In which colour is the particular feature shown, and why is it shown in this colour?
Are you able to identify new features which were not visible in the true-colour images?
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