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Microclimate inside air temperature radiation shields

Xiaomao Lin, University of Nebraska - Lincoln

Abstract

With the replacement of the Cotton Region Shelter (CRS), new air temperature observing systems such as the Automated Surface Observing System (ASOS), Maximum-Minimum Temperature System (MMTS), and the Gill shield temperature system were introduced. All of these systems house the air temperature sensor in radiation shields to prevent radiation loading on the sensors; a side-effect is that the air temperature entering a shield is modified by the interior solar radiation, infrared radiation, air speed, and heat conduction to or from the sensor so that the shield forms its own interior microclimate. The objectives of this study are to: (1) Theoretically investigate air temperature errors inside radiation shields. (2) Experimentally determine the air flow characteristics inside the shields. (3) Develop a physical model to understand the microclimate inside the shields including the interior solar radiation, infrared radiation, and air speed effects on the air (sensor) temperature under day and night conditions. (4) Experimentally estimate the effect of underlying ground surface coverings on the shield's interior solar radiation. Theoretical investigation, field experiments, and the energy balance modeling of temperature sensors were methodologies in this study. Parabolic curves described the fraction of solar radiation entering shields during the day light hours. This fraction increased as the ground solar reflectivity increased, except for the ASOS, as a function of time of day. The rank of solar radiation shielding effectiveness was ASOS > CRS > MMTS > Gill. The ASOS dew point sensor extracted heat from the mirror surface and heated or cooled the shield. The rank for the magnitude of unbalanced infrared radiation was ASOS > CRS > MMTS > Gill. Linear equations provided a reliable air speed estimation inside the shields based on the ambient wind speed. The air flow efficiency of shields (exception of ASOS) ranked as MMTS > CRS > Gill when the ambient wind speed was below 1m s−1 and ranked as Gill > MMTS > CRS when the ambient wind speed was more than 2 m s−1 . For all radiation shields, the air temperature corrected for shield effects was in good agreement between shields while the uncorrected “normal operating” temperatures were more variable from shield to shield.

Subject Area

Agronomy|Environmental science

Recommended Citation

Lin, Xiaomao, "Microclimate inside air temperature radiation shields" (1999). ETD collection for University of Nebraska-Lincoln. AAI9929212.
https://digitalcommons.unl.edu/dissertations/AAI9929212

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