Aarhus University Seal / Aarhus Universitets segl

Meteorologi

I forbindelse med målestationer for luftforurening foretages meteorologiske målinger. 

Teknisk beskrivelse (engelsk)
The meteorological sensors are located on a mast, which is placed on the buildings housing the roof stations. The measurements represents the meteorological conditions in the urban areas above roof level. The masts are 10 m high measured from the surface of the roofs. They are on top equipped with instruments for measuring wind speed and wind direction. At 2 m above roof level is instruments for measuring global radiation, relative humidity and temperature. All measurements are recorded every 10 sec. The recordings are converted to ½-hour mean values prior to the transmission to the central database.

 

Wind speed (Absalon, Risø National Laboratory):

The wind speed is measured with a cup anemometer with three carbon fiber cups. Every anemometer is calibrated individually in a wind tunnel. The standard deviation between the measured values and the linear regression line between measurements and the wind tunnel wind speed as determined with a pilot tube is typical around 0.02 m/s. The uncertainty of the pilot tube wind speed determination is around 0.08 m/s.

 

Wind direction (Risø National Laboratory):

The horizontal direction of the wind is determined with a light weight vane mounted on a vertical spindle. It is connected to a responder. The two output signals are proportional to the sine and cosine to the wind direction (0=north). The length constant for the vane is 1.5 m and the damping is 0.6.

 

Global radiation (Kipp & Zonen CM-11):

Measurement of the incoming solar and diffuse radiation is performed with a pyranometer. The measurements are characteristic for radiation having wavelength between 0.3 and 2.5 µm. The sensor consists of a light sensitive thermical bridge, which measures the increase in temperature for a black surface placed inside a glass housing. The absolute precision is better than 20 W/m2. The liniarity is better than 1% in the range from -4000 to 4000 W/m2.

 

Relative humidity (Rotronic):

The measuring principle is based on the humidity depending changes of the dielectric properties of a polymer. The sensor consists of a polymer foil placed between two electrodes. The capacity between the electrodes gives a measure of the humidity. The capacity is determined as the impedance for a high frequency electric signal. The Relative humidity is calculated on the basis of this measurement and the ambient temperature as determined by means of Pt100 platinum resistance thermometer.

 

Ambient temperature:

The thermometer included in the relative humidity equipment is used for registration of the temperature.