ABSTRACT
Satellite images are digital images recorded from specific spectral regions. Remote sensing systems detect radiation from various portions of a continuous spectrum of radiation, called the electromagnetic spectrum. Incoming solar radiation is often called insolation. About half of the solar radiation entering the atmosphere reaches the earth's surface and half is reflected or absorbed within the earth's atmoshpere. Reflection occurs when incoming radiation is redirected by a non-transparent surface. Absorption and transmittance both vary with wavelength. It is important to understand the characteristic spectral pattern of various natural features, especially in the spectral regions commonly used by satellite sensors for natural resources applications. Vegetation generally has low reflectance and low transmittance in the visible part of the spectrum. Near-infrared reflectance values are often more useful than visible reflectance values in distinguishing forest types such as aspen versus spruce. Pure water strongly absorbs radiation from the mid-infrared spectral region.
