Wind, air temperature, and water vapor pressure measurements are affected by surface type and roughness, soil moisture, regional topography, and obstructions. Sites selected for their applicability to a broader area should be free from obstructions such as buildings, trees, and steep slopes. Ten meter towers are often used to raise measurement heights above low-lying obstructions. The following table lists the suggested measurement heights and exposure (distance to an obstruction) for each type of sensor.
|Wind||3 m ±0.1 m recommended (AASC)|
2 m ±0.1 m, 10 m ±0.5 m, optional (AASC)
10 m (WMO & EPA)
|No closer than ten times the obstruction's height|
|Air Temperature & Relative Humidity||1.5 m ± 1 m (AASC)|
1.25-2.0 m (WMO)
2.0 m for temperature only (EPA) 2 m & 10 m for temperature difference (EPA)
|The sensor must be housed in a ventilated radiation shield to protect the sensor from thermal radiation. The EPA recommends the sensor be no closer than four times the obstruction's height and at least 30 m from large paved areas.|
|Solar Radiation||Height should be consistent with the exposure standard (AASC, WMO, EPA). To facilitate leveling/cleaning, CSI recommends installing at a height of 3 m or less.||The sky should not be blocked by any surrounding object. However, objects <10° above the horizontal plane of the sensor are allowed.|
|Precipitation||1.0 m ±0.2 m (AASC)|
30 cm minimum (WMO)
|AASC & EPA suggest the sensor be no closer than four times the obstruction's height. The orifice of the gage must be in a horizontal plane, open to the sky, and above the level of in-splashing and snow accumulation.|
|Soil Temperature||10 cm ±1.0 cm (AASC)|
5 cm, 10 cm, 20 cm, 50 cm, 100 cm (WMO)
|Measurement site should be 1 m² and typical of the surface of interest. The ground surface should be level with respect to the immediate (10 m radius) area.|
|The State Climatologist (1985) Publication of the American Association of State Climatologists: Heights and |
Exposure Standards for Sensors on Automated Weather Stations, v. 9, No. 4 October, 1985.
|EPA (1987). On-Site Meteorological Program Guidance for Regulatory Modeling Applications, EPA-450/4-87-013. |
Office of Air Quality Planning and Standards, Research Triangle Parks, North Carolina 27711.
|WMO (1983). Guide to Meteorological Instruments and Methods of Observation. World Meteorological Organization |
No. 8, 5th edition, Geneva Switzerland.
|Tanner, Bertrand D. (1990). Automated Weather Stations, Remote Sensing Reviews, 1990, Vol. 5 (1), p.73-98.|