In less than four months since launch, the first calibrated images are being delivered by ESA’s SMOS mission. These images of ‘brightness temperature’ translate into clear information on global variations of soil moisture and ocean salinity to advance our understanding of the water cycle.
Launched on 2 November, the Soil Moisture and Ocean Salinity mission is improving our understanding of Earth’s water cycle by making global observations of soil moisture over land and salinity over oceans. By consistently mapping these two variables, SMOS will not only advance our understanding of the exchange processes between Earth’s surface and atmosphere, but will also help to improve weather and climate models.
In addition, the data from SMOS will have several other applications in areas such as agriculture
and water resource management.
SMOS captures images of ‘brightness temperature’, which then require substantial processing to realise information on soil moisture and ocean salinity. Brightness temperature is a measure of the radiation emitted from Earth’s surface. During the commissioning phase, considerable effort is put into improving the quality of these images of brightness temperature before using them as input for the soil moisture and ocean salinity data products. ESA is now in a position to show the first results, which are very encouraging.
Since it was launched, engineers and scientists from various institutes in Europe have been busy commissioning the SMOS satellite and instrument.
This commissioning phase initially involved testing the Proteus platform and the all-important MIRAS instrument developed by EADS-CASA in Spain under contract to ESA. Both platform and instrument have shown excellent performance during their first four months in orbit.
Among other tasks, commissioning also includes testing the system that sends the data to the ground and the process through which the data is distributed, as well as calibrating the data products delivered by MIRAS.
Calibration and validation are a major undertaking in any Earth observation mission. Once the data get to the ground, they need to be checked that they make sense and can be used for scientific research. The last three months have been dedicated to performing these calibration activities in order to assess the performance of the mission.
This first calibration step is important to ensure the instrument meets the required performance. The process also includes making corrections for errors caused by, for example, temperature variations in the instrument’s antenna receivers or light reflected from the Sun and Moon. The effect is instantly visible in the calibrated image of Australia, where geophysical features, such as lakes, are clearly visible, compared to the uncalibrated image.
