France: European Space Agency (ESA) released first remote-sensing soil moisture data record spanning the period 1978 to 2010 – a predecessor of the data now being provided by ESA’s SMOS mission. Scientists will utilise this data to validate that water held in soil plays an important role in the climate system.
In 2009, ESA launched a dedicated satellite mission, SMOS, that provided high quality and direct measurements of soil surface soil moisture. While the key applications for SMOS data were weather forecasting, hydrology and water management, the mission also provided data in near-real time for operational applications.
To address the current lack of historical long-term soil moisture data for climate applications, ESA has been supporting the development of a global soil moisture data record derived by merging measurements acquired in the past by a series of previous and current European and US satellites.
These activities were initiated within the Water Cycle Multi-mission Observation Strategy project, led by ITC (The Netherlands), inside ESA’s Support To Science Element programme. The activities are now being continued and refined in the context of the Climate Change Initiative.
The 32 years of data allow for a robust calculation of the climatology, which in turn can be used to calculate anomalies. For example, areas of drying are evident, such as in the central US in 2005, Brazil and East Africa in the summer of 2007, southern China in the winter of 2009–10 and in 2010 in Russia.
Flooding is also evident, such as in Afghanistan in 1992, East Africa in 1998–99, Morocco in 2008 and the 2010–11 Queensland floods in Australia.
The data record was generated by merging two soil moisture datasets. The first is based on active microwave datasets processed by the Vienna University of Technology and is based on observations from the C-band scatterometers on Europe’s ERS-1, ERS-2 and MetOp-A satellites.
The other dataset was generated by the Vrije University of Amsterdam in collaboration with NASA, based on passive microwave observations from the Nimbus-7, DMSP, TRMM and Aqua missions.
The harmonisation of these datasets aimed to take advantage of both types of microwave techniques but proved difficult owing to sensor degradation, drifts in calibration and algorithmic changes in the processing systems.
Challenges also included guaranteeing consistency between the soil moisture data retrieved from the different active and passive microwave instruments.
Since this is the first release of such a product, an active cooperation of the remote sensing and climate modelling communities is required to validate the satellite data jointly to understand modelling results better.