The principles of remotely sensing sea surface salinity are briefly reviewed. The airborne instrument used for this study is a Scanning Low Frequency Microwave Radiometer (SLFMR). It has spatial resolution of typically 500m (depending on the altitude of the aircraft) and a salinity resolution of about 1 psu. This configuration is suitable for studying the dynamics of river plumes as they form on the continental shelf. The Burdekin River is one of Australia's major rivers with about 2.4% of the annual runoff from the continent. This river is in the dry tropics and has severe transient peaks which last for days to weeks during the summer monsoon season. The case study shows the river plume during growth and decay phases and is supported with in situ vertical profiles of water salinity and temperature. The river plume forms a classic low density layer at the surface, but its development and movement along the coast is a feature of the regional oceanography