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United States Department of Agriculture

Agricultural Research Service

Title: Effects of Instrument Shelters on Performance of Air Temperature and Humidity Measurements

item Dusek, Donald
item Howell, Terry

Submitted to: International Evapotranspiration Irrigation Scheduling Conference
Publication Type: Proceedings
Publication Acceptance Date: April 12, 1996
Publication Date: N/A

Technical Abstract: Automated agricultural weather stations often use naturally aspirated radiation shields for the air temperature and relative humidity sensors. A study was undertaken to compare a standard cotton belt shelter (CBS) widely used in the U.S. for manual weather observations with a naturally aspirated shield (NAT) and a forced aspirated (ASP) shield with the same type temperature and relative humidity sensor. Both the ASP and NAT shields ha temperatures about 1.8 to 2.1 deg C higher than observed in the CBS shield, but both were linearly correlated to CBS measurements with a slope near unity. Relative humidity indicated only about a 1.5% RH difference between the shields. The NAT and ASP shields affected temperatures enough to bias maximum daily air temperatures by 1.5 deg C (or about 8%), computed reference evapotranspiration by 0.6 mm d**-1 (or about 11%), or growing degree days (GDD) by 1 deg C-d. These differences are large enough to warrant a more thorough study of radiation shelters used in automated agricultural weather stations. These differences could significantly affect reliability of such data for irrigation scheduling or crop growth modeling purposes.

Last Modified: 4/19/2015
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