The SMOS satellite: On a mission to measure moisture
The level of moisture in the soil not only plays an important role in determining rates of plant growth, it also acts on a larger scale, as one of the major protagonists in the water cycle – the circulation of water vapour (and heat) between landmasses, the oceans and the atmosphere. If levels of soil moisture are low, the rate of evaporation falls. As a result, solar radiation heats the atmosphere more rapidly and thus raises air temperatures. “The European heat wave in the summer of 2003 was exacerbated by the fact that levels of soil moisture were very low“, says Professor Wolfram Mauser of the LMU’s Institute of Geography. “Soil moisture content also determines how much precipitation can be absorbed by the soil. If the soil is already saturated, the likelihood of flooding increases.“ In order to improve the accuracy and reliability of routine weather forecasts and long-term projections of future climatic conditions, more precise data on the water cycle are urgently needed.
The European satellite SMOS has been designed to collect and deliver these data. Thanks to the use of the latest sensor technology, SMOS will, for the first time, provide a global picture of soil moisture and ocean salinity from its vantage point in space. Both variables have profound effects on our climate: soil moisture contributes to atmospheric circulation, while differences in salinity and temperature drive oceanic circulation. The heart of the mission’s payload is the microwave sensor MIRAS. The instrument measures thermal radiation emitted by the Earth at a frequency of 1.4 Gigahertz, and levels of moisture and salinity have an especially strong influence on the intensity of emission in this band. Ground-based investigations in several European countries will gather and collate additional data from computer simulations, weather stations and aerial measurements made from research aircraft. These will enable researchers to calibrate and validate the remote measurements made by SMOS, and facilitate analysis of the satellite data. One of the largest of the so-called cal/val projects will be carried out in Southern Germany by investigators from LMU. A team of about 20 researchers will collect an extensive set of field observations in Eastern Bavaria at various times over the next month. The results will then be compared with those obtained by a research aircraft and those generated in computer simulations, and can thus serve as a check on the quality of the data transmitted to Earth by SMOS.
The observations made on the ground in the coming campaign will be supplemented by measurements made by a flying observatory from the Technical University of Helsinki. The plane will set off from Oberpfaffenhofen Reserach Airport to carry out reconnaissance flights over Bavaria on 8 days over the period from mid-May to mid-June of this year. The aircraft carries the same instrumentation as the SMOS satellite. The teams have high hopes for the new satellite. Consequently, the accompanying ground-based projects have been very carefully planned to make the most of the data collected by the “moisture mission”. The observations returned from space promise to provide new insights into the dynamics of water vapour exchange between landmasses, oceans and atmosphere, a cycle that has a considerable influence on the course of our weather and future prospects for our climate. “All the data will be incorporated into quantitative models of oceanographical, hydrological and meteorological processes“, says Professor Wolfram Mauser. “The ultimate aim is to improve the accuracy of our weather forecasts and our theoretical picture of future climatic change.“ (suwe)
The studies being done by the LMU team form part of the SMOSHYD project, which is supported by the German Aerospace Center (DLR).
For further information:
LMU Geography, SMOSHYD project:
German SMOS Project Office:
Prof. Dr. Wolfram Mauser
Phone: +49 (0) 89 / 2180 - 6674