However, we cannot usually get too specific in ouridentification based on reflectance. Hence objects can beidentified to some degree based on their "spectralsignature," or combination of reflectances in variousbands. In fact, any objectthat had a strong infrared signal and a weak red visible signalwould almost certainly be vegetation. Healthy vegetation absorbs most visiblelight, but strongly reflects infrared. Snow reflectsenergy strongly, which is why it appears white (the combinationof all visible light wavelengths).
For example, water reflectsvery little visible or infrared energy. Groups of objects on Earth have typical reflections of energythat help identify the objects.
Interpretation of remotely-sensedimages relies largely on these differences in reflection in thebands of energy that the satellite records. Water is darker than snow orconcrete, for instance. It's these differences in reflectivitythat enable us to identify objects through remote sensing. You can understand this idea if you think about how you canrecognize objects from the air: partly it's the differencesin color or brightness, as we saw when we discussedinterpretation of air photos. Objects on Earth,such as forests, water, pavement or snow all reflect differentamounts of energy. The Sun sheds plenty ofenergy on Earth in the visible and infrared bands. Satellites record this energy after it reflects off the surfaceof Earth and bounces back toward space. Objects on Earth Vary in How Much Energy They Reflect In addition to understanding energy bands, you alsoneed to know about how objects reflect energy, how satellitesrecord energy data, and how the data are assembled back on Earthinto picture-like images. Now we see a few more details about how satellite imageryworks. Exercise 7(e): How Satellite Imagery Works Geog 296: Contemporary GeographicTechniques Exercise 7: How Satellite Imagery Works
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