Energy Balance Model for Imagery and Electromagnetic Propagation

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  • 1 U.S. Army Research Laboratory, Battlefield Environment Directorate, White Sands Missile Range, New Mexico
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Abstract

The character of temperature and moisture gradients in the atmospheric surface layer is shown to be related to the intensity of visual distortions or “blurring” of images routinely detected by electo-optical systems and sensors. The authors are able to make quantitative approximations of the optical turbulence effect as represented by the refractive-index structure parameter C2n. Through the application of Monin-Obukhov similarity, the magnitudes of potential temperature and specific humidity gradients are determined using values of sensible and latent heat fluxes estimated from a semiempirical radiation and energy balance model. The model is constrained to require a minimum number of conventional meteorological inputs at a specific reference level (i.e., 2 m). These measurements include temperature, pressure, relative humidity, and wind speed. The model also requires a judgment of soil type and moisture (dry, moist or saturated), cloud characteristics (tenths of cloud cover, opacity, and an estimate of cloud height), day of the year, time of day, and longitude and latitude of the site of interest. Model concepts and equations are presented and several sample results are illustrated. Model estimates of net radiation; sensible, ground, and latent heat fluxes; and C2n are compared with measured values or values derived from measurements.

Abstract

The character of temperature and moisture gradients in the atmospheric surface layer is shown to be related to the intensity of visual distortions or “blurring” of images routinely detected by electo-optical systems and sensors. The authors are able to make quantitative approximations of the optical turbulence effect as represented by the refractive-index structure parameter C2n. Through the application of Monin-Obukhov similarity, the magnitudes of potential temperature and specific humidity gradients are determined using values of sensible and latent heat fluxes estimated from a semiempirical radiation and energy balance model. The model is constrained to require a minimum number of conventional meteorological inputs at a specific reference level (i.e., 2 m). These measurements include temperature, pressure, relative humidity, and wind speed. The model also requires a judgment of soil type and moisture (dry, moist or saturated), cloud characteristics (tenths of cloud cover, opacity, and an estimate of cloud height), day of the year, time of day, and longitude and latitude of the site of interest. Model concepts and equations are presented and several sample results are illustrated. Model estimates of net radiation; sensible, ground, and latent heat fluxes; and C2n are compared with measured values or values derived from measurements.

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