Measurements using Optic and RF Waves

Chapter 3Meteorological Visibility Measurement:Meteorological Optical Range¹

 

 

 

3.1. Introduction

Meteorological visibility, the possibility of seeing at a given distance, is, in origin, a quantity estimated by a human observer using natural or man-built reference markers at a known distance from the observation point (water or church towers, buildings, hill, groups of trees, rocks, lights etc.): if the observer can distinctly distinguish the outlines of one of the landmarks on the sky background, the meteorological visibility is at least equal to the distance which separates it from the point of observation.

However, its estimation is influenced by many subjective (presence of markers, perception and eye discerning capacity, etc.) and physical factors (solid and water vapor concentration in the air, hydrometeors (rain, snow, mist, etc)).

The essential meteorological quantity, namely the transparency of the atmosphere, can be measured objectively and it is called the meteorological optical range (MOR) or runway visual range (RVR).

After some definitions of terms related to the meteorological optical range, the atmosphere composition (gases, aerosols) and its effects on the light propagation (absorption, scattering and extinction) are presented. Then the different measurement methods of the meteorological optic range (visual estimate and instrumental measurements) are described. Instruments to measure the meteorological optical range can be classified into two groups: those which ...