SMOS data validation

Taking in soil moisture measurements

The radiation emitted by Earth and observed by SMOS is not only a function of soil moisture and ocean salinity. Therefore, to ensure that the data derived from the SMOS mission are correctly converted into units of moisture and salinity, the other effects that influence the signal need to be carefully accounted for.

The signal observed by SMOS is influenced by many different biophysical and geophysical variables other than soil moisture and ocean salinity. When measuring soil moisture these may come from vegetation, the understorey, the litter layer, the soil type and the varying roughness of the surface. Over the ocean, the signal can be influenced by waves and foam. The physical temperature of the surface of the land and sea is also important.

Radiometer used during the Wind and Salinity Experiment

To account for these effects in detail, various activities and dedicated campaign activities were conducted during the feasibility and design phases of the SMOS mission.

Intensive fieldwork carried out by large ground teams provided in situ information on surface temperature and surface cover from ground-based and airborne instruments operating at the same frequency as SMOS. Long-term observations were carried out from towers over land sites and from an oilrig platform in the Mediterranean.

Also, long-term observations of snow and ice-sheet surfaces have been conducted at the Concordia Station in Antarctica.

Many detailed results were obtained from these activities, which were vital in fine-tuning the retrieval concept so that SMOS provides the best data possible for soil moisture and ocean salinity.

Installing probes to measure soil moisture

For the purposes of validating soil moisture data now that SMOS is in orbit, the International Soil Moisture Network was set up by the Global Energy and Water Cycle Experiment (GEWEX) in cooperation with the Group on Earth Observations (GEO) and the Committee on Earth Observation Satellites (CEOS) and ESA.

The network provides an integrative platform to host quality controlled soil moisture measurements emerging from various ground validation campaigns and operational networks to share freely with the scientific community.

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