The automatic monitoring network (SwissMetNet) is equipped with high-precision measurement instruments and state-of-the-art communication technology. The monitoring programmes of the individual stations and the instruments used are defined according to the purpose of the monitoring station in question. All of the devices used comply with the standards of the Word Meteorological Organization (WMO).
Various measurement instruments are used within the monitoring network formed by the automatic ground-based stations (SwissMetNet). With Switzerland's complex topography and sometimes harsh weather conditions, developing and operating a monitoring network of this kind represents a particular challenge. All of the devices used comply with the specified certification criteria and the WMO standards regarding precision, ventilation and heating.
Temperature and humidity
MeteoSwiss uses the Thygan instrument produced by the Swiss company Meteolabor AG for its temperature and humidity measurements. The ventilated device meets very high standards in terms of measurement precision and is also suitable for use in elevated locations with extreme weather conditions. Temperature measurements are taken using a copper-constantan thermo-element, while humidity is measured with a dew point monitor. Here, a mirror in the hygrometer is cooled until moisture forms on its surface through condensation. The level of humidity can be calculated with precision on the basis of this dew point temperature.
The temperature and humidity sensors produced by Rotronic are housed in a weather and radiation shield with active ventilation. Temperature readings are taken using a platinum resistance thermometer (PT100). The relative humidity is determined on the basis of the changes in the properties of a hygroscopic polymer.
The two white sensors measure the air temperature on the surface and 5 cm above the ground using a platinum resistance thermometer (PT100). These temperature values provide frost hazard information and are used in the agricultural sector and in assessing road conditions. The surface temperature is also an important parameter in the area of boundary-layer meteorology.
This measurement instrument is used to measure the ground temperature at depths of 5, 10 and 20 cm. As with the devices used to determine the surface temperatures, the measuring principle for this instrument is based on a platinum resistance thermometer (PT100).
The atmospheric pressure is measured using a digital pressure measuring device produced by Vaisala. The devices stand out thanks to their high level of stability and precision. The PTB330 is delivered with three redundant BAROCAP® sensors, which guarantee high-quality measurements and outstanding reliability.
Wind direction and speed
The L14512 instrument produced by Lambrecht detects the wind direction based on the orientation of the wind vane; the position of the wind vane is determined using a potentiometer. The wind strength is measured on the basis of the rotational speed of the cup anemometer, whereby the number of rotations is proportionate to the wind speed.
The Ultrasonic Anemometer 2D tool produced by Thies calculates wind data with the help of ultrasonic signals. Two sets of sensor pairs are positioned perpendicular to one another. Here, the differences in the signal propagation times between the individual sensors are utilised, thus allowing the wind speed and direction to be determined
Amount of precipitation
MeteoSwiss uses 1518 H3 and 15188 pluviometers produced by Lambrecht to measure the amount of precipitation. The pluviometers are heated, meaning that solid precipitation such as snow is melted. The measuring system is based on a rocking mechanism. As soon at the container reaches its filling limit upon precipitation falling, it empties itself automatically via a tilting motion. The amount of precipitation is determined on the basis of the number of titling movements per unit of time.
The precipitation measurements of the Pluvio2 tool produced by Ott are based on the weighing principle. The volume of liquid, solid and mixed precipitation is calculated using a hermetically sealed load cell. The device distinguishes itself thanks to its high level of precision and low maintenance requirements. The modern electronics also simplify the process for checking the quality of the data. Unlike the measuring devices which work using the rocking principle, this device collects the precipitation in a reservoir that needs to be emptied regularly.
Duration of precipitation
The device produced by Thies registers the start and end of precipitation using a heated opto-electronic sensor. An infrared light barrier recognises precipitation in the form of drizzle, rain, snow and hail.
The CM 21 pyranometer produced by Kipp & Zonen measures shortwave hemispherical irradiance (305 - 2800 nm) using a thermopile. The measuring principle is based on a black-coated surface which is warmed up by solar radiation. This thermal energy is converted into measurable voltage which is used to calculate the incident radiation energy.
Hours of sunshine
The SPN-1 measuring device produced by Delta-T Devices measures hours of sunshine and shortwave irradiance. The measuring principle is based on seven independent thermopiles which are shaded to varying degrees by a screen (black plastic construction). Based on these different light conditions – at least one sensor is always in the shade – the sunshine duration and direct and diffuse radiation can be determined.
The Solar 111 B measuring device produced by Hänni records hours of sunshine. Six small independent photodiodes record the incident solar radiation. The solar cells are shaded successively at short intervals by the quickly rotating blades. All periods during which a minimum difference between uninterrupted radiation and the value when shading occurs is exceeded are classed as periods of sunshine. This device is no longer produced and is being replaced on a step-by-step basis by the SPN1 instrument manufactured by Delta-T Devices and described above.
The CG-4 pyrgeometer produced by Kipp & Zonen calculates incident longwave radiation. This primarily involves measuring the thermal (infrared) radiation emitted by the earth's surface and reflected back by the atmosphere. Whereas a transparent glass dome is used to measure shortwave irradiance, the CG-4 pyrgeometer uses a dark silicon dome which can only be penetrated by infrared radiation.
The IGS measuring device produced by Technidata measures the radioactive radiation (gamma dose rate) of the surrounding area. MeteoSwiss takes these measurements on behalf of the National Emergency Operations Centre. The use of these measurement instruments in SwissMetNet allows for the population to be warned quickly and in a targeted manner in instances of heightened radiation levels. The measuring device itself does not emit any radioactive radiation.