The project “Cosmic‑Ray Neutron Sensor for quantifying Non‑Rainfall Water Inputs (CoNRaWI)” was carried out jointly by the Helmholtz Centre for Environmental Research GmbH (UFZ) in Leipzig, Germany, and Ben‑Gurion University of the Negev in Israel. Funded by the German Federal Ministry of Education and Research (BMBF) and the Israeli Ministry of Science, Technology and Space (MOST) under the Joint German‑Israeli Water Technology Research Program, the 40‑month effort ran from 1 September 2019 to 31 December 2022. German principal investigators were Dr. Martin Schrön and Dr. Steffen Zacharias, while the Israeli lead was Prof. Nurit Agam. The German project number was 02WIL1522 and the Israeli number 15877‑3.
The scientific focus was to transfer the novel cosmic‑ray neutron sensing (CRNS) technology to the Negev desert and to evaluate its performance under extremely dry, low‑latitude conditions. CRNS exploits neutrons generated by cosmic rays that scatter off the ground; the reflected neutron flux is highly sensitive to near‑surface water content, with a horizontal footprint of tens of metres and a sensing depth of several decimetres. In the Negev, the method had not previously been tested, and the project aimed to determine its precision, robustness, and suitability for hydrological and agricultural applications.
Field work was concentrated at the Wadi Mashash Experimental Farm (31°80′89″ N, 34°85′39″ E, 400 m a.s.l.), a sandy‑loam Aridisol site with 13 % clay, 15 % silt, 72 % sand, and a porosity of 0.45. The long‑term mean annual rainfall is 115 mm, with precipitation mainly between October and May. The dry season (May–October) was the focus for non‑rainfall water inputs (dew, fog, direct vapor adsorption). Additional campaigns were carried out at Yeruham Lake and a jojoba field near Ashalim.
A CRNS system manufactured by Quaesta Instruments (USA) was installed in January 2021, replacing an earlier UFZ system in November 2021. The new instrument comprises two identical sensors, allowing cross‑validation and redundancy. During the dry season, the team discovered that the neutron signal in arid environments is strongly influenced by air humidity and the intensity of incoming cosmic radiation, effects that were not adequately corrected in existing algorithms. By conducting physics simulations and extensive field measurements, the researchers developed new correction methods that account for these variables. The improved processing pipeline reduced the uncertainty in daily soil‑moisture estimates to less than 0.5 Vol % at the Mashash farm, a precision that surpasses the previous state of the art for CRNS in deserts.
Beyond stationary monitoring, the project demonstrated the feasibility of mobile CRNS applications. By deploying the sensor on vehicles, the team identified wet spots beneath apparently dry surfaces in various farms, limans, and wadis, revealing fine‑scale heterogeneity in soil moisture that would otherwise remain undetected. These findings confirm that CRNS can resolve subtle changes in water content in arid environments and produce informative maps for farmland management.
The technical advances achieved—new correction algorithms, validated precision below 0.5 Vol %, and proven mobile deployment—make the method ready for operational use in hydrological modelling and agricultural water management. The collaboration has also prepared the technology for independent, private‑sector operation, positioning CRNS as a key tool for integrated water resource management in semi‑arid regions worldwide.