Cloud meter

• The laser ceilometer consists of a vertically located laser and a light receiver, usually a lidar , a receiver of laser light of the IR range. A laser pulse of a few nanoseconds is sent up into the atmosphere. While the beam passes through the aerosol, some of its energy is scattered on the aerosol particles, on particles with a size on the order of the wavelength of the laser beam. Due to the effect, called Mie scattering , part of the light is scattered back and caught by the ceilometer receiver. The delay time of the received signal can be recalculated into the distance.${\displaystyle \mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">d</span></span>}}$ {\ displaystyle d}   to the scattering point by the formula:

${\displaystyle \mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">d</span></span>}<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">=</span></span>\frac{\mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">c</span></span>}\mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">\delta </span></span>}\mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">t</span></span>}}{\mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">2</span></span>}}}${\ displaystyle d = {\ frac {c \ delta t} {2}}}  

where c is the speed of light in the air.

Thus, based on the analysis of time delays of a larger number of laser pulses, it is possible to construct an averaged vertical distribution of aerosol concentration in the atmosphere. In particular, it is possible to determine the height of the lower edge of the clouds.

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