Abstract

Local free-convection scaling is one of the obvious triumphs of boundary-layer similarity theory. In free convection there is no dynamic velocity scale; the sensible and latent heat fluxes, therefore, scale directly with the temperature and humidity structure parameters. By using scintillation to measure the refractive index structure parameter at two electromagnetic (EM) wavelengths, we can obtain the temperature and humidity structure parameters and, thus, in effect, measure path-averaged values of the sensible and latent heat fluxes. I describe this so-called two-wavelength method for free convection, derive quantitative guidelines for optimizing the method, and evaluate its potential accuracy. I show that the two-wavelength method works best when one EM wavelength is in the visible or infrared region and the other is in the millimeter or radio region. When the Bowen ratio the ratio of sensible to latent heat fluxesis between 5 and 0.1 or between 0.1 and 5, the expected accuracy of the measured heat fluxes is 1020% typical of what is possible with eddy-correlation measurements. However, with the two-wavelength method, the fluxes represent spatial averages.

© 1990 Optical Society of America