Visibility measurement is the most human-oriented measurement discussed because the objective of such measurement is to determine the distance at which humans (pilots, seamen, etc.) can see objects. Thus we are concerned with light that can be seen by humans (0.4 to 0.7μm), the way human eyes perceive such light, and then with the transparency of the atmosphere. Throughout this chapter, in the discussion of atmospheric transparency or absorption, the range of wavelengths from 0.4 (violet) to 0.7μm (red light) will be assumed. Cloud height is a remote sensing measurement but is included here because airport meteorological systems usually include a cloud height sensor. According to the WMO, meteorological visibility by day is defined as the greatest distance that a black object of suitable dimensions, situated near the ground, can be seen and recognized when observed against a background of fog, sky, etc. Visibility at night is defined as the greatest distance at which lights of moderate intensity can be seen and identified.
THz generation from laser-induced breakdown in pressurized molecular gases: on the way to terahertz remote sensing of the atmospheres of Mars and Venus
