Spectral Bands and Multispectral Imaging

Multispectral imaging systems record reflected and emitted energy in a small number of discrete, non-overlapping wavelength intervals, or bands, rather than capturing a single broadband image the way an ordinary camera does. Landsat 8's OLI instrument, for example, defines separate bands for coastal aerosol (0.43-0.45 micrometers), blue (0.45-0.51), green (0.53-0.59), red (0.64-0.67), near-infrared (0.85-0.88), and two shortwave-infrared bands (1.57-1.65 and 2.11-2.29 micrometers), with its companion TIRS instrument adding two thermal-infrared bands near 10.9 and 12.0 micrometers. Because different materials, soil, water, healthy vegetation, stressed vegetation, and various minerals, reflect and absorb energy differently across these bands, comparing a pixel's values across bands, rather than examining any single band in isolation, is what allows analysts to distinguish and classify surface materials.