Integration of in-situ and Cosmic-Ray Neutron Sensing derived soil moisture measurements into the observation network of the German Meteorological Service – progress of the project IsaBoM

The need to measure soil moisture accurately and continuously and to monitor its climatic impact has moved into the public focus through the rising number of flood events and droughts in recent years. Currently the German Meteorological Service (DWD) operates a soil moisture viewer based on the soil-vegetation-atmosphere-model AMBAV and provides agrometeorological consultation. In addition to modelled soil moisture data, several institutions and some federal states started to set up their own soil moisture observations locally, but a nationwide observation network is still lacking in Germany.

The DWD’s internal project IsaBoM (“Integration of standardized and automatized soil moisture measurements in the DWD observation network”) aims to prepare the introduction of automized soil moisture measurements with two complementary measuring systems (in-situ sensors and Cosmic-Ray Neutron Sensing - CRNS), following the guidelines of the WMO (World Meteorological Organization) to permanently monitor this essential climate variable. The project’s tasks are, amongst other aspects, testing and selecting suitable sensors and calibration procedures, setting up data analysis methods, preparing the automatic dataflow and public data provisioning and ultimately providing solutions to integrate the soil moisture data into the existing operational models.

Here, we present the progress of the project IsaBoM for the preparation of a nationwide soil moisture network starting with 20 preliminary designated stations of the DWD’s operational network, where the chosen locations are representative of the soil properties and climatic conditions throughout Germany, while also being equally distributed geographically. We report on first results from our two test sites in Braunschweig and Dürnast (Freising), where the parallel measurements of multiple arrays of in-situ sensors and several CRNS sensors are tested on two operational DWD measurement sites differing in soil type and climate and providing additional meteorological measurements. We show first comparisons of soil moisture estimates from CRNS detectors with different sensitivities and the observed effects of precipitation, vegetation cover and irrigation on the signal.  The CRNS signals at both stations are calibrated using repeated soil sampling campaigns with varying equipment. Additionally, experimental sensor layouts (arrangement of in-situ profiles towards the CRNS) are used to further test the comparability and synergies between the two systems.

Feasible solutions and means for the optimal utilization of both soil moisture measuring systems, while adapting to the particular conditions when deployed on operational meteorological measurement sites, are discussed with regards to the chances and challenges from the perspective of a meteorological service.