Use of Cosmic-ray Neutron Sensing for soil water management

Accurate soil moisture (SM) monitoring is key in climate modeling, hydrological observations and irrigation as it can greatly improve water use efficiency, the understanding of energy transfer over the land surface and ground water dynamics. Recently, Cosmic-Ray Neutron Sensors (CRNS) have been recognized as a promising tool in SM monitoring due to their large footprint of several hectares and half a meter in depth. Using this technique one can relate the flux density of albedo neutrons generated in cosmic-ray induced air showers to the amount of water in the environment. CRNS have great potential as to the non-invasive nature of the method and the low-maintenance independently operating sensors. In the last years this type of sensor has been integrated into several national and international monitoring networks like COSMOS, COSMOS-UK, ADAPTER and TERENO sites. Initially, CRNS instruments have relied on the use of a scarce material - helium-3. In order to scale up the method and to reduce costs within the CosmicSense research group recently large-scale instruments have been developed using alternative technologies including readout electronics and data acquisition systems. With a more economical operation the initial focus on hydrological research Cosmic-Ray Neutron Sensors are emerging into applied agricultural contexts, for example irrigation management and soil moisture mapping. Examples are the integration of CRNS into the SWAMP (LoRa) or the Nb-IoT network of the German Chamber of Agriculture. This project, called ADAPTER, involves the development and provision of innovative simulation-based information products for weather- and climate-resilient agriculture. These are daily (”soil”) weather and comprehensive long-term climate change information available to the agricultural community and all interested parties as easy-to-use analyses, data products with forecasts, and information interfaces. Still, challenges for CRNS are posed for scenarios especially for irrigated fields with a size smaller than the CRNS footprint or heterogeneous conditions with respect to the biomass distribution.