Lagos - Exercises using Landsat data
|  | Landsat 7 ETM | |
Description of Landsat data
The US satellite Landsat 7 ETM is NASA's 6th operational Earth observation satellite of this series (the launch of Landsat 6 failed in 1993). It is the latest in this series of Earth observation satellites dating back to 1972.
The Landsat system holds the longest continuous record of the Earth's surface.
The main tasks of all Landsat satellites are environmental monitoring, disaster assessment, land use and regional planning, cartography, range management, and oil and mineral exploration.
Landsat's mode of operation has been continuously improved throughout the years. Today, the Landsat ETM features 8 channels, from visible light (channels 1,2,3) to near and middle infrared (channels 4,5,7) and thermal radiation (channel 6). The ground resolution is 15 metres for the panchromatic channel (8) and 30 metres for channels 1 to 5 and 7. The thermal channel 6 provides a resolution of 80 metres. The Landsat 7 satellite operates in a circular, sun-synchronous, near polar orbit.
See the Technical data of Landsat bands table.
| | | Lagos, 2 February 2000 |
Description of the Lagos images
Open the LEOWorks programe. If you have not downloaded the images of Lagos yet, do so now.
Open the images. Choose File>Open. A dialogue box will pop up. Choose the folder Lagos and select the first image Lagos_Landsat_Band_1.tif. Open all the other single band images, too.
All the images need to be improved in brightness and contrast.
Select (activate) the first image Lagos_Landsat_Band_1.tif and choose Enhance>Histogram Equalization. The image will change. Convert all other images in the same way.
There are now 9 images on your screen. Every single image reflects a part of the electromagnetic spectrum between 0.45 µm and 12.5 µm (the part of the visible light ranges from 0.45 µm to 0.7 µm).
There are so many different bands because different features of the Earth's surface can be seen in different parts of the electromagnetic spectrum and the same features appear unequal in different parts of the spectrum. That means that all the imaged features or objects appear to us in different colours when illuminated with light (including infrared). In order to distinguish the objects by their colour we need an instrument capable of measuring in many bands, covering all the visible colours including the infrared sector.
Now have a look at the images and group them into two categories of similar appearance. Note the water and the north-eastern area of vegetation in particular.
Compare the two groups with the table containing the different Landsat data bands. Are these two groups identifiable here, too?
What is the significant difference between the images Lagos_Landsat_Band_61.tif and Lagos_Landsat_Band_62.tif and the rest of the images?
What is the special feature of lagos_landsat_pan.tif?
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