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Remote Sensing - a tool for environmental observation

4 post classification analysis the two or more images

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4. Post-classification analysis: The two (or more) images acquired at different dates are first independently classified using the same legend (number of classes and type of classes). Next, the two images are overlaid and compared by subtracting or otherwise. It should be noted that the accuracy of the change detection depends on the accuracies of each of the individual classification results and the geometric match of the imagery. Detailed description of change detection studies are available in Mas (1999) and Singh (1989).
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95 6.5 Imaging Spectroscopy As already discussed in chapter 2, imaging spectroscopy refers to the acquisition of images in many, very narrow, contiguous spectral bands in the optical part of the spectrum (figure 2.5). Absorption features in soil and vegetation spectra are caused by the interaction between electro- magnetic radiation (photons) and matter at the level of molecules and electrons. Two major types of interaction cause diagnostic features in reflectance spectra throughout the optical region: electronic processes and vibrational processes: Electronic transitions refer to the changes in the energy state of electrons bound to atoms, molecules or crystal lattices. Electronic processes produce rather broad absorption bands for the weathered materials found at the soil surface. These bands occur mostly in the ultraviolet (< 0.4 μm) and extend as overtones with diminishing frequency into the visible and near infrared. Vibrational transitions refer to the very small displacements of atoms from their equilibrium positions induced by radiation. Vibrational processes produce relatively very sharp absorption bands for the weathered materials found at the soil surface (Hunt and Salisbury, 1970). No bands due to the fundamental vibrational modes occur in the range short of 2.5 μm. All features observed in the range short of 2.5 μm are exclusively overtones or combinations of tones of fundamental processes in the middle and far infrared (Hunt and Salisbury, 1976, 1970). Imaging spectrometers are nowadays also available aboard satellite systems. The first experiences with imaging spectrometry were with experimental sensors such as AVIRIS and GERIS . The first successful use of imaging spectroscopy was a mineral mapping campaign at Cuprite, Nevada (Kruse et al., 1990). Spectra of kaolinite, alunite and hematite could clearly be identified in the airborne images. Although the results were very good, this technique of mineral and soil mapping is fairly limited to bare or sparsely vegetated areas. At this moment two spaceborne spectrometers are operational: MODIS: Moderate resolution Imaging Spectrometer and ASTER. MODIS is a 36-channel spectrometer with bands in visible, near infrared, shortwave infrared and thermal wavelengths, its main objective is to collect information for ocean and cloud research. It will has a spatial resolution of 250 m: http://modis.gsfc.nasa.gov/ . Aster has bands in visible, near and mid infrared and thermal infrared. More information is available on: http://asterweb.jpl.nasa.gov/default.htm 6.6 Remote Sensing projects in the Netherlands
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