Initial Analyses and Demonstration of a Soil Moisture Smart Sensor Web

We have developed a new concept for a smart sensor web technology for measurements of soil moisture that include spaceborne and in-situ assets. The objective of the technology is to enable a guided/adaptive sampling strategy for the in-situ sensor network to meet the measurement validation objectives of the spaceborne sensors, with respect to resolution and accuracy. One potential application is the Soil Moisture Active/Passive (SMAP) mission, The sensor nodes are guided to perform as a macroinstrument measuring processes at the scale of the satellite footprint, hence meeting the requirements for the difficult problem of validation of satellite measurements. The science measurements considered are the surface-to-depth profiles of soil moisture estimated from satellite radars and radiometers, with calibration and validation using in-situ sensors. Satellites allow global mapping but with coarse footprints. The total variability in soil-moisture fields comes from variability in processes on various scales. Installing an insitu network to sample the field for all ranges of variability is impractical. However, a sparser but smarter network can provide the validation estimates by operating in a guided fashion with guidance from its own sparse measurements. The feedback and control take place in the context of a dynamic data assimilation system. The overall design of the smart sensor web including the control architecture, assimilation framework, and actuation hardware will be presented in this paper. We also present results of initial numerical and laboratory demonstrations of the sensor web concept, which includes a small number of soil moisture sensors and their measurement model, a dynamic soil moisture time-evolution model (SWAP), and an optimal control strategy. Based on these results, the TRL has been advanced to 3 from the initial level of 2.