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Sherwood B. Idso

Abstract

Calculations of the mean daily transmittance of the atmosphere for solar radiation based on only one independent variable, surface vapor pressure, are demonstrated to be equally as accurate for Phoenix, Ariz., as similar calculations averaged on a monthly basis over several years. A correlation coefficient of 0.92 is obtained for the linear regression of the calculated on the measured values, with a standard error of estimate of only 0.009.

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Sherwood B. Idso

Abstract

Eighteen years of clear day solar radiation data accumulated at Phoenix, Ariz., are analyzed to yield monthly averages of the transmittance of the atmosphere for solar radiation. These figures serve as a basis against which theoretical calculations of the atmospheric transmittance are compared. Calculations based upon the complete set of attenuation relations proposed by Houghton average 2% lower than the measurements. When Houghton's water vapor absorption curve is replaced by the McDonald water vapor absorption relation, however, the yearly averages of the measurements and calculations are essentially identical. A procedure for approximating the effects of dust variability is introduced which further improves even these calculations in terms of monthly comparisons.

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PICTURE OF THE MONTH

Thunderstorm Outflows: Different Perspectives over Arid and Mesic Terrain

Sherwood B. Idso

Abstract

No abstract available.

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Sherwood B. Idso, Ray D. Jackson, and Robert J. Reginato

Abstract

A procedure is developed for removing data scatter in the thermal inertia approach to remote sensing of soil moisture that arises from environmental variability in time and space. It entails the utilization of nearby National Weather Service air temperature measurements to normalize measured diurnal surface temperature variations to what they would have been for a day of standard diurnal air temperature variation, arbitarily assigned to be 18°C. Tests of the procedure's basic premise on a bare loam soil and a crop of alfalfa indicate it to be conceptually sound. It is possible the technique could also be useful in other thermal inertia applications, such as lithographic mapping.

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Sherwood B. Idso, Ray D. Jackson, and Robert J. Reginato

Abstract

A simple laboratory technique is described for making rapid emittance measurements with an infrared thermometer. It is shown that when the infrared thermometer head is held flush against a surface, its output is a linear function of surface emittance. Thus, viewing two or more surfaces of known emittance in this manner “calibrates” the infrared thermometer, so that viewing an unknown surface at the same temperature in this manner will yield its emittance., Emittance values of the standard surfaces employed may be obtained via any of a variety of emittance measurement methods previously developed. A nomograph is presented that shows the possible errors that can occur as a result of temperature differences that may exist between the test and standard surfaces.

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