coSMOS: Field Validation of the SMOS Soil Moisture Retrieval Algorithm
Michael Berger, Yann Kerr and Jeffrey Walker
SMOS is ESA’s “Water Mission” with the dual objectives of providing global Soil Moisture and Ocean Salinity observations. This will be the first satellite mission enabling scientists to study and better understand the water cycle, its dynamics, and the possible impact of climate change. Near-surface soil moisture will be derived from multi-angular, dual-polarisation L-band brightness temperature data reconstructed from SMOS observations. The retrieval scheme currently being developed for the SMOS ground segment processor is based on decision tree accounting for the land surface heterogeneity that assigns different radiative transfer models according to the relevant land cover type. These radiative transfer models are constrained by auxiliary information such as soil texture and vegetation characteristics, accounting for the various contributors of the emitted brightness temperature at L-band. In order to validate the retrieval concept a field campaign for verifying the soil moisture retrieval algorithm of SMOS (coSMOS) has been designed. CoSMOS was originally planned to take place in Europe in spring 2005, to cover different wetness and vegetation conditions within the growing season. Due to the unavailability of a suitable aircraft in Europe for that time it had to be postponed. A new opportunity derived for November 2005 as a co-operation with the Australian’s National Airborne Field Experiment (NAFE’05) which will take place in the Goulburn River Catchment, about 200 km W of Newcastle, Australia (see www.nafe.unimelb.edu.au). This site is being intensively monitored and studied for soil moisture, and was setup specifically for remote sensing verification and assimilation studies (see www.sasmas.unimelb.edu.au). Permanently installed monitoring stations provide meteorological data and soil moisture profiles. Intensive field measurements of near-surface soil moisture and supporting data are planned for the whole campaign period of 31 October to 25 November. The core coSMOS instrument will be the refurbished TUD EMIRAD polarimetric L-band radiometer, flown aboard an Aero Commander aircraft, and the core NAFE instrument will be a Polarimetric L-band Multibeam Radiometer (PLMR) flown aboard a motor glider. The Aero Commander will also be equipped with a thermal infrared radiometer and the motor glider will have a thermal imager, tri-spectral scanner, and digital camera. This co-operation with NAFE allows coSMOS to keep the original objectives, to provide data in time for the SMOS ground processor validation activities planned for early 2006, and to prepare for the SMOS validation during commissioning phase. This paper is intended to outline the specific campaign objectives and the derived airborne and in-situ measurement requirements.