Section 1. Preparation and Siting

1.3 Siting and Exposure

CAUTION If any part of the weather station comes in contact with power lines, you could be killed. Contact local utilities for the location of buried utility lines before digging or driving ground rods.

Selecting an appropriate site for the weather station is critical in order to obtain accurate meteorological data. In general, the site should be representative of the general area of interest, and away from the influence of obstructions such as buildings and trees.

The weather station should not be located where sprinkler irrigation water will strike sensors or instrument enclosure.

Some general guidelines for site selection are listed below, which were condensed from EPA (1988)1, WMO (1983)2, and AASC (1985)3 publications.

1.3.1 Wind Speed and Direction

Wind sensors should be located over open level terrain, and at a distance of at least ten times (EPA) the height of any nearby building, tree or other obstruction, as illustrated in Figure 1.3-1.

Standard measurement heights:

3.0 m ± 0.1 m recommended (AASC)

2.0m ± 0.1 m, 10.0 m ± 0.5 m optional (AASC)

10.0m (WMO and EPA)

1.3.2Temperature and Relative Humidity

Sensors should be located over an open level area at least 9 m (EPA) in diameter. The surface should be covered by short grass, or where grass does not grow, the natural earth surface. Sensors should be located at a distance of at least four times the height of any nearby obstruction and at least 30 m (EPA) from large paved areas. Sensors should be protected from thermal radiation, and adequately ventilated.

Situations to avoid include:

•large industrial heat sources

•rooftops

•steep slopes

•sheltered hollows

•high vegetation

•shaded areas

•swamps

•areas where snow drifts occur

•low places holding standing water after rains

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