Australia: To ensure the integrity of an Earth observation mission, it is often essential to compare the data being delivered from space with measurements taken on the ground. Accordingly, the first field campaign to validate soil moisture data from European Space Agency’s (ESA) Soil Moisture and Ocean Salinity (SMOS) mission has been carried out in Australia.
The campaign to validate soil moisture data was recently completed in southeast Australia. The field campaign, called Australian Airborne Calibration/Validation Experiments for SMOS (AACES ) was led by the University of Melbourne and funded by the Australian Research Council. The airborne and in situ data collection strategy covered a 500 km transect of the Murrumbidgee Catchment in southeast Australia. The experience gained in earlier campaigns carried out for SMOS, such as the Australian National Airborne Field Experiment in 2005, ensured the campaign was well planned and ran smoothly.
The data collected in Australia will be fed into the International Soil Moisture Network, which is a new system initiated 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 International Soil Moisture Network will bring together data collected in field campaigns worldwide and provide a standardised global database to share freely with the scientific community.
The next campaign, which will continue the process of validating soil moisture and also include the validation of ocean salinity data, will be carried out by ESA in cooperation with the French space agency CNES in Europe. Between April and July, several sites in Denmark, Germany, France and Spain will be observed from the air while teams take coincident ground-truth measurements as SMOS orbits above.
Launched in November, SMOS mission is still being commissioned, but already delivering its first calibrated images of ‘brightness temperature’. As a measure of radiation emitted from Earth’s surface, these images can be used to derive global measurements of soil moisture and ocean salinity to improve our understanding of the water cycle. In addition, data from SMOS will help to improve weather and climate models, and have applications in areas such as agriculture and water resource management.
Both the observed brightness temperature data and the derived data products for soil moisture from SMOS need to be validated. To achieve this, data were collected from the air and on the ground. A light aircraft carrying an L-band radiometer and a thermal imager was used to make observations similar to those acquired by SMOS, while data on soil moisture were collected by a team on the ground.