COMPARISON OF TWO OPTICAL METHODS FOR MEASURING LINE AVERAGES OF THERMAL EXCHANGES ABOVE WARM WATER SURFACES.

Abstract

The evaluation of the heat fluxes requires estimates of the surface friction velocity and the ratio of the sensible to latent heat fluxes, each of which can be obtained with sufficient accuracy over a warm water surface from relatively simple measurements of temperatures and wind speeds. The direct visual measurements are highly reproducible and, since the equipment is easily deployed in the field, the thermal performance of different sections of the same pond can be evaluated rapidly. Agreement within 10% is found between values of the heat fluxes estimated by these methods and those obtained from low-level bulk-aerodynamic procedures, but only if lines of sight are chosen to ensure that fetch is adequate, particularly for the mirage observations.