RAINFOR GEM Intensive Plots Manual (pdf) - University of Oxford

appropriate equipment. We recommend Campbell Scientific Automatic Weather Stations(http://www.campbellsci.co.uk/index.cfm?id=105: see TEAM 2011 for recommendations for all components),although other devices such as Skye MiniMET stations(http://www.skyeinstruments.com/category/products/minimet-weather-station/) are in use across the network.Measurements in the clearingIn the absence of a tower, the primary MET station should be set up in a clearing as close as possible to thecensus plot. As emphasised in TEAM (2011), the clearing should be no smaller than 70 m 2 and whereverpossible located away from sloping ground, hollows or valleys, permanently-shaded areas, swamps and lowplaces that hold water after rain (however note the sloping ground around the MET station pictured above:these are guidelines and it is frequently not possible to avoid sloping ground). The implicit assumption in allmeteorological measurements is that sensors are positioned at a height which is representative of a homogenousland cover below. Therefore, meteorological measurements are made using sensors mounted on a tower ofsufficient height to make representative measurements of the land cover below.For areas of short grass/bare ground, position the MET station following the ‘level 2’ siting guidelines ofTEAM (2011), i.e. following the 4H and 2H rules illustrated in the figure above (from TEAM 2011). Thescreen height of the MET station should be set at 2 m above the ground (WMO 2008) which gives anacceptable footprint for upwelling radiation measurements (with a sensor height of 2 m, 90% of the fluxoriginates from a circle of diameter 12 m on the surface). Apart from the precipitation gauge, all equipmentshould be mounted as close as possible 98 to screen (reference) height on the station tower.98 n.b. “close” is a relative term here: within a metre or so is fine for above-canopy measurement, e.g. photo above, although forbelow-canopy work they should be somewhat closer, e.g. photo below. Also, note that in TEAM (2011) the temperature and humiditysensors are at 2 m height but the radiation sensor is at 3 m.76