Glossary

Glossary

Albedo The ratio of reflected radiation (light) to incident radiation (light). Albedo values range from 0 (pitch black) to 1 (perfect reflector).
Apparent Surface Reflectance At-sensor radiance that has been transformed from units of radiance to percent reflectance. By accounting for and removing effects of atmospheric scattering, the result is more representative of surface reflectance.
At-sensor Radiance Radiance (e.g. W/m2/nm/sr) measured by the spectrometer. This measurement inherently includes scattering from the atmosphere. 
Electromagnetic Spectrum The range of all frequencies of electromagnetic radiation, which includes gamma rays, x-rays, ultraviolet light, visible light, infrared light, microwaves and radio waves. Terrestrial remote sensing primarily deals with visible and infrared radiation, or wavelengths ranging from approximately 350 nanometers (nm) to 2500 nm (see spectral bandwidth and spectral range).
Imaging Spectroscopy The study of light as a function of wavelength that has been emitted, reflected or scattered from a surface or medium.
Imaging Spectrometer Sometimes called a hyperspectral sensor, an instrument used to study light that has been reflected or scattered from a surface or medium. Imaging spectrometers typically measure light in contiguous, narrow wavelengths (channels) across a portion of the electromagnetic spectrum. Sensors that measure radiation in a few broad channels that are not contiguously spaced are not considered spectrometers (e.g. Landsat).
Spectral Bandwidth The width of an individual spectral channel in the spectrometer. The narrower the spectral bandwidth, the narrower the spectral feature the spectrometer will accurately measure. 
Spectral Range The range of the electromagnetic spectrum detected by the sensor or spectrometer, often expressed in micrometers (μm), nanometers (nm) or millimeters. Spectral ranges commonly used in remote sensing include ultraviolet (UV; 0.001 to 0.4 µm); visible (0.4 to 0.7 µm); near-infrared (NIR; 0.7 to 3.0 µm); mid-infrared (MIR; 3.0 to 30 µm); and the far infrared (FIR): 30 µm to 1 mm.