Skylab L-band microwave radiometer observations of soil moisture revisited

In preparing for future L-band passive microwave soil moisture satellite missions, investigators have employed ground, aircraft and satellite sensors. Of the satellite sensors, there has been only one instrument that provides any heritage at L-band: the Skylab S-194 instrument that operated in the 1970s. Here a dataset from the S-194 was located and recovered. Data from these Skylab missions have been analysed and reported in a few applications, however, these studies utilized limited validation and exploited only a portion of the data collected. In this investigation we explored the use of products from climate model reanalysis projects as ancillary or alternative validation data. Analyses showed that the reanalysis outputs were not accurate and would be of limited value. Tests using a radiative transfer based soil moisture retrieval algorithm matched the observations available for validation. These results support the use of this approach as a tool in understanding a wider range of vegetation condition effects on soil moisture retrieval.