Training Module on Monitoring Vegetation From Space

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• 2 - Physical concepts
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• 2.1 - Radiation principles
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• 2.2 - Interactions with matter
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• 2.3 - The effect of the atmosphere
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• 2.4 - Spectral signature of an object
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• 2.5 - Bidirectional reflection

2.4 - Spectral signature of an object

The reflectance values for different objects, over a range of wavelengths, may be plotted for comparison. Such plots are called "spectral response curves" or "spectral signatures." Differences among spectral signatures of landscape features are used to help classifying remotely sensed scenes, since the spectral signatures of similar features have similar shapes.

Figure 2.10 shows the spectral signatures of 3 different materials: conifers (in green), water (blue) and soil (red).

Figure 2.10: Spectral response curves for 3 different types of features on the surface of the Earth.

The previous figure implies that the mentioned feature types are normally spectrally separable. The degree of separation of landscape features depends, however, on the range of wavelengths we are considering. This means that two features may be indistinguishable for a certain spectral range and perfectly individualized for other spectral band.