As you'll see later, land use and land cover mapping were previously accomplished by visual inspection of photographic imagery. At longer, near- and mid-infrared wavelengths, however, the two types are much easier to differentiate. Notice that the reflectances within the visual band are nearly identical. The two lines represent the spectral response patterns of conifer and deciduous trees. The next graph demonstrates one of the advantages of being able to see beyond the visible spectrum. (California Institute of Technology, 2002.) To explore the spectral response characteristics of thousands of natural and man made materials, visit the ASTER Spectral Library. Knowing their typical spectral response characteristics, it is possible to identify forests, crops, soils, and geological formations in remotely sensed imagery, and to evaluate their condition.įigure 8.5.1 The spectral response patterns of brownish-gray soil (mollisol), grass, and water. Water absorbs most incoming radiation across the entire range of wavelengths. Brownish gray soil reflects more energy at longer wavelengths than grass. About half of the incoming near-infrared radiation is reflected, however, which is characteristic of healthy, hydrated vegetation. Like most vegetation, the chlorophyll in grass absorbs visible energy (particularly in the blue and red wavelengths) for use during photosynthesis. The graph shows that grass, for instance, reflects relatively little energy in the visible band (although the spike in the middle of the visible band explains why grass looks green). The graph below illustrates the spectral response patterns of water, brownish gray soil, and grass between about 0.3 and 6.0 micrometers.
The magnitude of energy that an object reflects or emits across a range of wavelengths is called its spectral response pattern. The various objects that make up the surface absorb and reflect different amounts of energy at different wavelengths. The rest is either reflected by the atmosphere, or absorbed and re-radiated as infrared energy. The Earth's land surface reflects about three percent of all incoming solar radiation back to space.
0 kommentar(er)
