5.2 Temperature and relative humiditySensors should be located over an open, level area at least 9 m (29.5 ft) (EPA) in diameter. Thesurface 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 nearbyobstruction and at least 30 m (98.43 ft) (EPA) from large paved areas. Sensors should beprotected from thermal radiation and adequately ventilated.Situations to avoid include:l large industrial heat sourcesl rooftopsl steep slopesl sheltered hollowsl high vegetationl shaded areasl swampsl areas where snow drifts occurl low places holding standing water after rains5.3 Solar radiationPyranometers should be located to avoid shadows on the sensor at any time. Mounting it on thesouthernmost (northern hemisphere) portion of the weather station will minimize the chance ofshading from other weather station structures. Reflective surfaces and sources of artificialradiation should be avoided.5.4 Soil temperatureThe measurement site for soil temperature should be at least 1 m2 (10.76 ft2) and typical of thesurface of interest. The ground surface should be level with respect to the immediate area of 10 m(32.81 ft) radius.Standard measurement depths:10.0 cm ± 1.0 cm (4 in ± 0.4 in) (AASC)5.0 cm, 10.0 cm, 50.0 cm, 100.0 cm (2 in, 4 in, 19.7 in, 39.4 in) (WMO)Section 5. Siting and exposure 11
