Toward the Development of Protocols for Soil Moisture Measurement and Monitoring (Invited Presentation)

Soil moisture has been identified as an essential climate variable by the World Meteorological Organization and there is a wealth of research and data being collected to document soil moisture state throughout the world. However, these measurements and methods have not been standardized toward a harmonized protocol causing variability and inaccuracies to be introduced into literature. Therefore, it is urgent and necessary to develop a system of protocols for the calibration and validation of soil moisture measurements to guide future soil moisture networks and field campaigns. A survey of current methods used in monitoring soil moisture via networks will be presented along with results of a testbed which monitors long term trends in sensor performance. Various in situ sensors have been shown to estimate soil moisture with significant biases and distributions for the same location, which can dramatically influence soil moisture applications. There is a long history of field experimentation which has resulted in a current set of common practices, which will be reviewed and discussed, with attention given to variations to account for different landscapes. Satellite remote sensing missions will be discussed as well, including methodologies for calibration and validation of satellite products. The Soil Moisture Active Passive (SMAP) Mission and the Soil Moisture Ocean Salinity (SMOS) missions will be reviewed as well as past missions, such as the Advanced Microwave Scanning Radiometer (AMSR-E) and Aquarius. These have various criteria for mission success with standardized baseline metrics, such as an unbiased root mean squared error of less than 0.04 m3/m3 for a set of core validation sites (SMAP and SMOS).