Remote sensing technology has a huge potential for improving hydrologic prediction through soil moisture measurement. This is particularly so given that the first dedicated soil moisture satellite is to be launched in 2007; the Soil Moisture and Ocean Salinity (SMOS) mission. However, targeted field experiments must be undertaken now so that immediate use can be made of this data when it becomes available. Therefore a series of National Airborne Field Experiments (NAFE) are being planned and conducted throughout south-eastern Australia. The first of these experiments was undertaken in the Goulburn Catchment of the Upper Hunter during November 2005, and the second experiment will be undertaken in the Murrumbidgee Catchment during November 2006. The ultimate objective of these campaigns is to mature soil moisture retrieval algorithms, downscaling and data assimilation, such that 1km near-surface and root-zone soil moisture mapping can become an operational product from SMOS. The idea is that higher resolution remote sensing data from MODIS may be used to downscale the 50km SMOS pixels to 1km resolution. While the first campaign had a specific focus on providing high resolution data for process level understanding of these objectives, the second campaign is focussed on practical application to the SMOS mission. To this end a light aircraft is being used to collect SMOS-type data using a Polarimetric L-band Multibeam Radiometer (PLMR), together with supporting instruments (thermal imager, tri-spectral scanner, lidar and digital photographs). Moreover, extensive ground soil moisture data is collected for verification purposes. This paper describes the airborne field experiment to be undertaken in the Murrumbidgee catchment and its role in maturing this important catchment state variable. See www.nafe.unimelb.edu.au for more detailed information on these experiments.