SMOS ground validation in Australia : results from summer and winter campaigns

With the recent launch of the Soil Moisture and Ocean Salinity (SMOS) mission the remote sensing community is becoming engaged in airborne campaigns for their validation. This study covers two aspects, the actual ground validation and also the requirements of spatial coverage. Both campaigns covered an extensive area of up to 20 independent SMOS footprints and the relationship of the large scale averages with the SMOS observations is presented here. The latter point is necessary, given the financial and logistical constraints on the area that can be covered by airborne simulators, giving scientifically sound advice on the fractional footprint coverage requirements by campaigns for these low resolution sensors a paramount importance. Using high resolution airborne data from two extensive airborne campaigns in south-eastern Australia the fractional coverage requirement for L-band passive microwave satellite missions is assessed using a sub-sampling technique of the flight lines through a passive microwave footprint. It is shown that a minimum 50% coverage of the total footprint size will typically be required to ensure that the correct footprint mean is estimated with an expected sampling error of less than 4K; the design sensitivity of SMOS.