Measurements of the Air Temperature Profile near the Ground by Two Laser Beams

Abstract

Two neon-helium gas lasers were used for temperatures profile measurements near the ground. The experiment was carried out during the cold season (when absolute humidity is small on the asphalt pavement) to be free from humidity effects. The light path length from the source to the target was 25 m. Height changes of the two laser beams at the target, about 0.03 and 0.08 m high, were measured by sight. Simultaneous measurements were made of the air temperature profile by a platinum resistance thermometer, of the ground surface temperature by a radiation thermometer, and of the solar radiation by a solar-cell radiometer. Temperature profiles were analyzed, assuming the log-linear profile of air temperature, using light beam deflection data at two levels and the temperature at one level. The profile obtained compares with the directly observed temperature profile. The friction temperatures estimated by optical means have better correlations to solar radiation than those from direct temperature measurement. During the experiment the asphalt ground surface was sometimes wet from drizzle; in such a case the temperature profile was not so simple as log-linear but showed a small temperature minimum at a height of 0.01 or 0.02 m due to evaporation of steam fog just above the surface.