High Frequency Microwave Amplifiers to Improve Weather Prediction using Satellites

The European Space Agency (ESA) will be launching a series of new weather satellites that will be able to measure important meteorological data, such as precipitation, water vapor and temperature, better than ever before. The core of these measuring devices are some extremely sensitive microwave amplifiers that have been developed at the Fraunhofer Institute for Applied Solid State Physics IAF. These satellites can perceive even very weak signals from the environment, which are important for more accurate weather predictions.

In meteorologist community, there is the joke that the weather tomorrow can be predicted best when assuming that it will be the same as today. The common belief is that this would be true in many cases. However meteorologist would rather rely on computer simulations which are fed with thousands of pieces of measurement data. For many years, such data have mainly been supplied by satellites that use sensitive sensors to measure the temperature or the precipitation on earth. The better these sensors are, the more accurate the measured values and, therefore, also the weather predictions. In the next few years, the European Space Agency (ESA) will be launching the second generation of its MetOp weather satellites (Meteorological Operational Satellites), which are equipped with state-of-the-art measurement technology. There will be a total of six satellites. A total of EUR 1.4 billion has been earmarked for the construction of the second-generation MetOp satellites – launch and operation not included.

With the satellites, small but very fine technological components from the Fraunhofer Institute for Applied Solid State Physics IAF in Freiburg will also be launched. These will include highly precise amplifiers that measure microwave radiation. This radiation is emitted from every single object, every surface – similar to how a body radiates heat, which can be seen in the infrared image. The amplifiers are calibrated to microwave frequencies because these provide important meteorological information: they capture microwaves emitted by water vapor, rain, fog or ice crystals - particularly also from the ice crystals in the cirrus clouds high up in the atmosphere, which are believed to have an important effect on the climate and weather. Thanks to the microwave radiation, it is also possible to reach very precise conclusions about the temperature on the ground.

The signals received by the microwave antennas of the satellites are extremely weak, these are usually only a few nanowatts strong. In order to be able to detect these microwave signals with any degree of reliability, amplifiers are needed. The amplifiers from the Fraunhofer IAF have proven to be ideal for such applications. According to Dr. Michael Schlechtweg, who heads the High Frequency Electronic business unit at the Fraunhofer IAF - The core of these amplifiers is a transistor from the semiconductor material indium gallium arsenide. A characteristic of this material is that it is very easily traversed by electrons, even if the electric field that drives the electrons is very small. Accordingly, the electrons in the transistor are already set in motion by very weak microwave signals, which makes the transistor extremely sensitive. This amplifier will help the MetOp satellite to determine temperature, water vapor and type of precipitation even more precisely in the future. This increases the reliability of the weather forecast.

On the MetOp satellite, the amplifiers are used in three different microwave instruments which measure different things – precipitation, water vapor, ice crystals and the temperature. For this purpose, the experts working with Schlechtweg had to produce different sensors, each of which is calibrated to the corresponding microwave frequency – in concrete terms, there are five frequency bands between 54 and 243 GHz. As Schlechtweg explains, a value of 243 GHz is a considerable value, since, the higher the frequency, the more powerful the amplifier has to be. The components of the Fraunhofer IAF are a significant breakthrough, and they have gathered interest from US Companies as well.