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Landsat ETM

RGB means red (channel 3), green (channel 2) and blue (channel 1) and uses the physical features of the additive colour system.

The colours of the different features depend on the bands selected for the combination, because every land cover has its own spectral fingerprint. Different combinations produce different images of the same feature. We will try out some of these in the following exercises.


a) True-Colour Combination

The true-colour combination requires the Red (band 3 - 0.63 - 0.69 µm), the Green (band 2 - 0.52 - 0.60 µm) and the Blue (band 1 - 0.45 - 0.52 µm) Landsat channels. This combination leads to an image closely resembling a colour photograph.

Open the LEOWorks programme. If you have not downloaded the images of Niger Inland Delta yet, do so now.

Choose File>Open. A dialogue box will pop up. Choose the folder Niger and select the first image Nigerdelta_Landsat_Band_1.tif. Open Nigerdelta_Landsat_Band_2.tif and Nigerdelta_Landsat_Band_3.tif, too.

Choose Image>Combine from>...Red Green Blue. A pop-up menu will open. Select images Nigerdelta_Landsat_Band_1.tif for Red, Nigerdelta_Landsat_Band_2.tif for Green, and Nigerdelta_Landsat_Band_3.tif for Blue, and click OK.

The new image is the true-colour image produced from the three visible light channels. But it is not in true colours yet, because of the unenhanced data. Select (activate) the first image Nigerdelta_Landsat_Band_3.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 Input 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.

False-colour combination of the Niger Inland Delta using bands 7, 4, 2

To increase the interpretability of satellite images, false-colour images are often used.

In most cases a false-colour image uses at least one infrared channel. The infrared range is very useful for interpreting the Earth's surface, because it consists of reflected and emitted energy.

Infrared is not visible to the human eye but transmits a lot of information. Plants in particular reflect much more energy in the near infrared than in the visible range of the electromagnetic spectrum. Even the health status of a plant can be ascertained from the intensity. Sometimes false-colour images even uncover invisible features.

Which are the unseen features in the true-colour image of the Niger Inland Delta?

Are there hidden parts of vegetation or water surfaces?

Open the LEOWorks programme. If you have not downloaded the Niger Inland Delta images yet, do so now.

Choose File>Open. A dialog box will pop up. Choose the folder Niger and select the first image Nigerdelta_Landsat_Band_2.tif. Open Nigerdelta_Landsat_Band_4.tif and Nigerdelta_Landsat_Band_7.tif.

Choose Image>Combine from...>Red Green Blue. A pop-up menu will open. Select image Nigerdelta_Landsat_Band_7.tif for Red, Nigerdelta_Landsat_Band_4.tif for Green and Nigerdelta_Landsat_Band_2.tif for Blue, and click OK. Improve the raw data the same way you did for the 'True-Colour Combination' exercise.

	False-colour combination of the Niger Inland Delta using bands 4, 3, 2.

Choose File>Open. A windows dialog box will pop up. Choose the folder Niger and select the first image Nigerdelta_Landsat_Band_2.tif. Open Nigerdelta_Landsat_Band_3.tif and Nigerdelta_Landsat_Band_4.tif, too.

Choose Image>Combine from...>Red Green Blue. A pop-up menu will open. Select image Nigerdelta_Landsat_Band_4.tif for Red, Nigerdelta_Landsat_Band_3.tif for Green and Nigerdelta_Landsat_Band_2.tif for Blue, and click OK. Improve the raw data the same way you did for the 'True-Colour Combination' exercise.

There is a lot of water in the Niger Inland Delta region. But vegetation (shown in red) is rare in this part of the image. Explain the reasons for the sparse vegetation cover.

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