Two different remotely sensed land surface temperature ( T _s) products are compared with in situ observations from the National Airborne Field Experiment research site in the western part of the Murrumbidgee catchment, Australia. The remotely sensed T _s products are retrieved from the following: 1) Ka-band passive microwave (MW) observations using several of space-based MW radiometers and 2) thermal infrared observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) on two satellite platforms. Both methods show similar accuracy when compared to ground observations, although the dynamic range and mean differ significantly. However, a direct comparison of the two products at the same overpass time reveals a strikingly constant relation, with a standard error of ~ 4 K. The results of this study indicate that a merged T _s product of both MODIS and MW observations is feasible and would decrease the amount of data gaps and increase the sampling frequency for this region to 12 observations a day.