Exercise 1: Display of satellite images
Objective: Introduce students to the basic operations needed to display satellite data of the Araucanía Region.
Data: To perform this exercise you need to download the LEOWorks programme and the Landsat 7 satellite image of 24 March 2003 which is in the Villaricca.zip file. You can download both from the menu on the right.
The following five bands are available:
Villarrica_2003_B1.tif
Villarrica_2003_B2.tif
Villarrica_2003_B3.tif
Villarrica_2003_B4.tif
Villarrica_2003_B5.tif
The bands correspond to the Thematic Mapper sensor as follows:
Band 1: 0,45 - 0,52 μm (blue)
Band 2: 0,52 - 0,60 μm (green)
Band 3: 0,63 - 0,69 μm (red)
Band 4: 0,76 - 0,90 μm (near infrared)
Band 5: 1,55 - 1,75 μm (mid-infrared or SWIR)
Open and save an image
Open LEOWorks.
Open the data in LEOWorks using Open multiple images as a single file.
Show all bands in the Viewer and select Window/Tile Evenly.
Improve the image contrast of each band by Interactive Stretching, e.g.adjust the sliders to cover 95% of all pixels in the band. To compare the five bands, select Synchronise compatible product views and cursor position in the Navigation window.
Inspect the images and find the best bands to differentiate between lakes, vegetation , volcanic features and snow, and record your findings in a table like the one below.
| | Band (s) | | Lake | | | Vegetation | | | Volcanic features | | | Snow | |
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Can you explain your findings?
Using the ‘Pixel info’ inspection tool, we will now compare the reflection from water and vegetation by observing the pixel values. Record your findings in a table like the one below.
| Pixel value | Band 1 | Band 2 | Band 3 | Band 4 | Band 5 | | Water | | | | | | | Vegetation | | | | | |
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Compare your findings with the graph shown below.
Which bands show a better differentiation between water and vegetation?
Spectral signatures of soil, vegetation and water, and spectral bands of Landsat 7
Construct a colour RGB image using band4 for red, band5 for green, and band3 for blue. Improve the image contrast using Interactive Stretching, e.g. adjust the sliders to cover 95% of all the pixels in the band.
Describe the image.
Study the typical spectral signature of objects such as water, soil, vegetation, etc. presented in the graphic. It shows the reflection from different surfaces for each band in the Landsat image.
Identify the colours of the volcanoes and lakes, as well as the town of Villarrica.
Try to explain the colours using the information in the tables above, together the graph.
Example of an annotated image showing Lake Villarrica, the Villarrica Volcano, and Lake Colico
Try other band combinations to obtain a better differentiation of these objects and decide which combinations are the two best ones.
Save them with an appropriate name, e.g. Villarrica-RGB-4-5-3.tif (if you have chosen band4 in red, band5 in green and band3 in blue).
Using the toolbar in the final viewing, you can enlarge, reduce, and study the image information and the histograms of the different bands.
Create a map.
The Map tool can be used to create an annotated map. It is possible to draw lines and rectangles as well as write text on an image.
Create a map with the names of the volcanoes, lakes, and towns.
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