An empirical vegetation correction for soil water content quantification using cosmic ray probes

Cosmic ray probes are an emerging technology to continuously monitor soil water content at a scale significant to land surface processes. However, the application of this method is hampered by its susceptibility to the presence of aboveground biomass. Here we present a simple empirical framework to account for moderation of fast neutrons by aboveground biomass in the calibration. The method extends the N0-calibration function and was developed using an extensive data set from a network of 10 cosmic ray probes located in the Rur catchment, Germany. The results suggest a 0.9% reduction in fast neutron intensity per 1 kg of dry aboveground biomass per m2 or per 2 kg of biomass water equivalent per m2. We successfully tested the novel vegetation correction using temporary cosmic ray probe measurements along a strong gradient in biomass due to deforestation, and using the COSMIC, and the hmf method as independent soil water content retrieval algorithms. The extended N0-calibration function was able to explain 95% of the overall variability in fast neutron intensity

Validation of spaceborne and modelled surface soil moisture products with cosmic-ray neutron probes

The scale difference between point in situ soil moisture measurements and low resolution satellite products limits the quality of any validation efforts in heterogeneous regions. Cosmic Ray Neutron Probes (CRNP) could be an option to fill the scale gap between both systems, as they provide area-average soil moisture within a 150–250 m radius footprint. In this study, we evaluate differences and similarities between CRNP observations, and surface soil moisture products from the Advanced Microwave Scanning Radiometer 2 (AMSR2), the METOP-A/B Advanced Scatterometer (ASCAT), the Soil Moisture Active and Passive (SMAP), the Soil Moisture and Ocean Salinity (SMOS), as well as simulations from the Global Land Data Assimilation System Version 2 (GLDAS2). Six CRNPs located on five continents have been selected as test sites: the Rur catchment in Germany, the COSMOS sites in Arizona and California (USA), and Kenya, one CosmOz site in New South Wales (Australia), and a site in Karnataka (India). Standard validation scores as well as the Triple Collocation (TC) method identified SMAP to provide a high accuracy soil moisture product with low noise or uncertainties as compared to CRNPs. The potential of CRNPs for satellite soil moisture validation has been proven; however, biomass correction methods should be implemented to improve its application in regions with large vegetation dynamics

Analyzing and modelling solute and sediment transport at different spatial and temporal scales : a case study of the catchment of the Wahnbach River, Germany

Solute and sediment transport processes occur on a wide range of temporal and spatial scales. Differentiate between the observation and process scale which are defined by the extent, spacing and support of the samples and the modelling scale. Typical modelling scales are the local scale (1m), the hillslope scale (100 m), the catchment scale (10 km) and the regional scale (1000 km) and in time the event scale (1 day), the seasonal scale (1 yr) and the long-term scale (100 yrs). The modelling scale often differs from the process scale which necessitate an upscaling, downscaling or regionalization scheme. In this study process investigations at different scales are used for the temporal and spatial upscaling of a physically-based erosion model (OPUS) and its validation at different temporal and spatial scales. Numerous models for simulating erosion, transport and sedimentation are available. While the USLE model is able to simulate long-term erosion at single slopes without considering sedimentation, other approaches are calculating all processes. In this study a concept for continuously modelling of solute and sediment transport at the catchment scale for a period of 50 years is presented. The simulation is based on the application of the model system OPUS designed for long-term simulations of agricultural processes. As OPUS is a hillslope model the catchment is discretized into numerous slopes. These slopes are linked via a channel model (HEC6-model) which allows the simulation of erosion, transport and sedimentation in a catchment. After introducing some modifications and enhancements of the model it was possible to simulate interflow induced by macropores with OPUS. The simulation results are compared with measurements at different spatial and temporal scales of a meso-scale catchment used for drinking water supply. Three small sub-catchments of 22 to 29 ha are used to validate the model at the local scale. The modified and validated model is then applied to the Wahnbach catchment with an area of about 54 km². Simulations at the local and the catchment scales are presented and compared with measurements. To model the long-term behaviour of solute and sediment transport with a deterministic model a complete set of climate and landuse data is necessary. In this case study a method was developed to overcome the lack of data by using a weather generator. The long-term catchment simulations are validated by determining the mass of sediments trapped in the drinking water reservoir. In general, the obtained simulation results at different scales (from the sub-catchment scale to the catchment scale and from single events to long-term scales) are encouraging. It could be shown that process-based models can be applied at several scales in order to calculate the fluxes of matter. Furthermore, the results show that the considered flux types (water, solutes, sediment) are simulated with different success. The best results are obtained by simulating daily runoff at the sub-catchment scale and at the catchment scale. The solute concentration at the sub-catchment scale and the monthly nitrate discharge at the catchment scale is reproduced satisfactory, but the measures of model accuracy are less high. The sediment transport is simulated with the lowest accuracy

Root Zone Sensors for Irrigation Management in Intensive Agriculture

Crop irrigation uses more than 70% of the world’s water, and thus, improving irrigation efficiency is decisive to sustain the food demand from a fast-growing world population. This objective may be accomplished by cultivating more water-efficient crop species and/or through the application of efficient irrigation systems, which includes the implementation of a suitable method for precise scheduling. At the farm level, irrigation is generally scheduled based on the grower’s experience or on the determination of soil water balance (weather-based method). An alternative approach entails the measurement of soil water status. Expensive and sophisticated root zone sensors (RZS), such as neutron probes, are available for the use of soil and plant scientists, while cheap and practical devices are needed for irrigation management in commercial crops. The paper illustrates the main features of RZS’ (for both soil moisture and salinity) marketed for the irrigation industry and discusses how such sensors may be integrated in a wireless network for computer-controlled irrigation and used for innovative irrigation strategies, such as deficit or dual-water irrigation. The paper also consider the main results of recent or current research works conducted by the authors in Tuscany (Italy) on the irrigation management of container-grown ornamental plants, which is an important agricultural sector in Italy

Soil water content in southern England derived from a cosmic-ray soil moisture observing system - COSMOS-UK

Cosmic-ray soil moisture sensors have the advantage of a large measurement footprint (approximately 700 m in diameter) and are able to operate continuously to provide area-averaged near-surface (top 10-20 cm) volumetric soil moisture content at the field scale. This paper presents the application of this technique at four sites in southern England over almost 3 years. Results show the soil moisture response to contrasting climatic conditions during 2011-2014, and are the first such field-scale measurements made in the UK. These four sites are prototype stations for a UK COsmic-ray Soil Moisture Observing System (COSMOS-UK), and particular consideration is given to sensor operating conditions in the UK. Comparison of these soil water content observations with the Joint UK Land Environment Simulator (JULES) 10 cm soil moisture layer shows that these data can be used to test and diagnose model performance, and indicates the potential for assimilation of these data into hydro-meteorological models. The application of these large-area soil water content measurements to evaluate remotely-sensed soil moisture products is also demonstrated. Numerous applications and the future development of a national COSMOS-UK network are discussed

Evaluation of the ZigBee based wireless soil moisture sensor network SoilNet

A remaining challenge in hydrology is to explain the observed patterns of hydrological behaviour over multiple spacetime scales as a result of interacting environmental factors. The large spatial and temporal variability of soil water content is determined by factors like atmospheric forcing, topography, soil properties and vegetation, which interact in a complex nonlinear way (e.g. Western et al., 2004). A promising new technology for environmental monitoring is the wireless sensor network (Cardell-Oliver et al., 2005). The wireless sensor network technology allows the real-time soil water content monitoring at high spatial and temporal resolution for observing hydrological processes in small water-sheds (0.1-80 sqkm). Although wireless sensor networks can still be considered as an emerging research field, the supporting communication technology for low cost, low power wireless networks has matured greatly in the past decade (Robinson et al., 2008). Wireless environmental sensor networks will play an important role in the emerging terrestrial environmental observatories (Bogena et al., 2006), since they are able to bridge the gap between local (e.g. lysimeter) and regional scale measurements (e.g. remote sensing). This paper presents a first application of the novel wireless soil water content network SoilNet, which was developed at the Forschungszentrum Jülich using the new low-cost ZigBee radio network

Sensor-to-sensor variability of ECH2O EC-5, TE and 5TE sensors used for wireless sensor networks

Towards an improvement of measurement accuracy for the low-budget soil water content sensors ECH2O EC-5, TE and 5TE used in the wireless sensor network SoilNet, the application of a sensor-specific calibration procedure based on dielectric standard liquids reduce the RMSE of approximately 0.010 to 0.015 cm^3 cm^-3 in high soil water content range

Schlussbericht

Ziel des Teilprojekts war es, die Bodenfeuchte in Westafrika durch ein skalenäquivalentes Mess- und Modellierungskonzept besser zu charakterisieren. Hierzu sollten neuartige Cosmic-Ray-Neutronensonden (CRNS) eingesetzt, optimiert und in bestehende Messnetzwerke (z. B. WASCAL) integriert werden. Die CRNS-Technologie sollte dabei helfen, die räumlich-integrative Erfassung der Bodenfeuchte zu verbessern, die Validierung satellitengestützter Produkte zu unterstützen und hydrologische Modelle robuster zu parametrisieren. Die installierten CRNS-Stationen lieferten hochwertige Bodenfeuchtedaten. Basierend auf diesen und anderen CRNS-Daten wurden neue, datengetriebene Skalierungsparameter entwickelt, die die Genauigkeit der Bodenfeuchtebestimmung zu erhöhen. Weiterhin wurde eine flächendeckende Simulation des Wasserhaushalts und der Brutto-Primärproduktion (Gesamtrate der Photosynthese) über Ghana mit dem Landoberflächenmodell CLM5 durchgeführt und mit lokalen Bodenfeuchtedaten, sowie Daten meteorologischer und hydrologischer Stationen validiert. Herausforderungen wie geopolitische Unsicherheiten und Geräteschäden konnten durch Umplanung kompensiert werden. Das Teilprojekt wurde in enger Zusammenarbeit mit KNUST, der Universität Augsburg und WASCAL durchgeführt und lieferte Beiträge zu mehreren internationalen Publikationen und Konferenzen