The first generation of public earth observation began with LandSat 1. Images from space had previously only been used by the military. Today imagery can be purchased with spatial resolutions from 1 km to 60 cm, covering everywhere in the world. Images derived from optical satellites (NOAA, LandSat, IRS, IKONOS) can be either panchromatic (256 or more shades of gray), multispectral (the light spectrum broken into a limited number of broad bands) or hyperspectral (the spectrum broken into a large number of narrow bands).

Images can also be obtained from radar or SAR satellite (RADARSAT-1, ERS-1 and 2, JRS) which can emit radar in a variety of wavelengths, polarities and look-angles. Look angle determines the amount of terrain and soil effects that will be observed.

Resolution is the smallest area that can be observed by the satellite. In general, for a satellite with 20 m resolution, each picture element is made up from the reflectance from an area on the earth measuring 20 x 20 m. This is overly simplistic and the stronger the contrast, the smaller the object can be detected. With SAR imagery, backscatter often reduces the stated resolution.