A first CRNS cluster for soil moisture retrieval designed for comparison with remote sensing

Cosmic-ray neutron sensing (CRNS) is a non-invasive method to retrieve root zone soil moisture as daily time series for an area integrated that is up to 0.1 km². This area can be expanded by combining several CRNS-stations into one cluster, not only increasing its extent as an integral but also allowing for differences inbetween them to represent spatially varying conditions. Such a cluster has been established in Maquardt, Potsdam, Germany end of 2019, with a mixed land use of cropped fields, meadows and orchards. This CRNS cluster has been expanded by additional CRNS stations and side measurements during 2023 to improve its capability to serve as soil moisture reference network for satellite remote sensing such as the ESA Sentinel-1 Earth Observation mission. This was part of the EU-wide collaboration project SoMMet addressing soil moisture observations from a metrological perspective, with a focus on CRNS to bridge the scale between point measurements and remote sensing.
We will outline the design and capabilities of this specific CRNS cluster. It includes not only 16 CRNS stations, partly with very high device sensitivity, but also a soil moisture network of point sensors, as each CRNS stations includes a profile soil moisture probe down to 40 cm at least and additional shallow soil moisture measurements at 5 and 15 cm depths. Overall, this constitutes a triple network (CRNS, shallow soil moisture, root-zone soil moisture) covering about completely 0.5 km²; in its core area CRNS stations are placed densely, and with spacing increasing to the outside an outer area of about 2 km² is covered in a non-dense way. CRNS stations were individually calibrated by individual measurement campaigns to achieve a high-accuracy and representativeness for its location. We will present first results from the first-year of operation (2024) in its final, full cluster design and discuss its value in respect to future use as reference network or establishment as fiducial reference measurement.

Acknowledgment: The project Cosmic Sense has received funding from German Research Foundation (DFG, roject number 357874777) and the project 21GRD08 SoMMet has received funding from the European Partnership on Metrology, co-financed from the European Union’s Horizon Europe Research and Innovation Programme and by the Participating States.