@article{JagdhuberHajnsekBronstertetal.2013,
  author    = {Jagdhuber, Thomas and Hajnsek, Irena and Bronstert, Axel and Papathanassiou, Konstantinos Panagiotis},
  title     = {Soil moisture estimation under low vegetation cover using a multi-angular polarimetric decomposition},
  series = {IEEE transactions on geoscience and remote sensing},
  volume    = {51},
  journal   = {IEEE transactions on geoscience and remote sensing},
  number    = {4},
  publisher = {Inst. of Electr. and Electronics Engineers},
  address   = {Piscataway},
  issn      = {0196-2892},
  doi       = {10.1109/TGRS.2012.2209433},
  pages     = {2201 -- 2215},
  year      = {2013},
  abstract  = {The estimation of volumetric soil moisture under low agricultural vegetation from fully polarimetric synthetic aperture radar (SAR) data at L-band using a multi-angular polarimetric decomposition is investigated. Radar polarimetry provides the framework to decompose the backscattered signal into different canonical scattering mechanisms referring to scattering contributions from the underlying soil and the vegetation cover. Multiangular observation diversity further increases the information space for soil moisture inversion enabling higher inversion rates and a stable inversion performance. The developed approach was applied on the multi-angular L-band data set acquired by German Aerospace Center's ESAR sensor as part of the OPAQUE campaign in 2008. The obtained results are compared against ground measurements collected by the OPAQUE team over a variety of vegetated agricultural fields. The validation of the estimated against ground measured soil moisture results in an root mean square error level of 6-8 vol.\% including all test fields with a variety of crop types.},
  language  = {en}
}
@article{LohmannTietjenBlaumetal.2012,
  author    = {Lohmann, Dirk and Tietjen, Britta and Blaum, Niels and Joubert, David F. and Jeltsch, Florian},
  title     = {Shifting thresholds and changing degradation patterns: climate change effects on the simulated long-term response of a semi-arid savanna to grazing},
  series = {Journal of applied ecology : an official journal of the British Ecological Society},
  volume    = {49},
  journal   = {Journal of applied ecology : an official journal of the British Ecological Society},
  number    = {4},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {0021-8901},
  doi       = {10.1111/j.1365-2664.2012.02157.x},
  pages     = {814 -- 823},
  year      = {2012},
  abstract  = {1. The complex, nonlinear response of dryland systems to grazing and climatic variations is a challenge to management of these lands. Predicted climatic changes will impact the desertification of drylands under domestic livestock production. Consequently, there is an urgent need to understand the response of drylands to grazing under climate change. 2. We enhanced and parameterized an ecohydrological savanna model to assess the impacts of a range of climate change scenarios on the response of a semi-arid African savanna to grazing. We focused on the effects of temperature and CO2 level increase in combination with changes in inter- and intra-annual precipitation patterns on the long-term dynamics of three major plant functional types. 3. We found that the capacity of the savanna to sustain livestock grazing was strongly influenced by climate change. Increased mean annual precipitation and changes in intra-annual precipitation pattern have the potential to slightly increase carrying capacities of the system. In contrast, decreased precipitation, higher interannual variation and temperature increase are leading to a severe decline of carrying capacities owing to losses of the perennial grass biomass. 4. Semi-arid rangelands will be at lower risk of shrub encroachment and encroachment will be less intense under future climatic conditions. This finding holds in spite of elevated levels of atmospheric CO2 and irrespective of changes in precipitation pattern, because of the drought sensitivity of germination and establishment of encroaching species. 5. Synthesis and applications. Changes in livestock carrying capacities, both positive and negative, mainly depend on the highly uncertain future rainfall conditions. However, independent of the specific changes, shrub encroachment becomes less likely and in many cases less severe. Thus, managers of semi-arid rangelands should shift their focus from woody vegetation towards perennial grass species as indicators for rangeland degradation. Furthermore, the resulting reduced competition from woody vegetation has the potential to facilitate ecosystem restoration measures such as re-introduction of desirable plant species that are only little promising or infeasible under current climatic conditions. On a global scale, the reductions in standing biomass resulting from altered degradation dynamics of semi-arid rangelands can have negative impacts on carbon sequestration.},
  language  = {en}
}
@article{deFigueiredodeAraujoMedeirosetal.2016,
  author    = {de Figueiredo, Jose Vidal and de Araujo, Jose Carlos and Medeiros, Pedro Henrique Augusto and Costa, Alexandre C.},
  title     = {Runoff initiation in a preserved semiarid Caatinga small watershed, Northeastern Brazil},
  series = {Hydrological processes},
  volume    = {30},
  journal   = {Hydrological processes},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {0885-6087},
  doi       = {10.1002/hyp.10801},
  pages     = {2390 -- 2400},
  year      = {2016},
  abstract  = {This study analyses some hydrological driving forces and their interrelation with surface-flow initiation in a semiarid Caatinga basin (12km(2)), Northeastern Brazil. During the analysis period (2005 - 2014), 118 events with precipitation higher than 10mm were monitored, providing 45 events with runoff, 25 with negligible runoff and 49 without runoff. To verify the dominant processes, 179 on-site measurements of saturated hydraulic conductivity (Ksat) were conducted. The results showed that annual runoff coefficient lay below 0.5\% and discharge at the outlet has only occurred four days per annum on average, providing an insight to the surface-water scarcity of the Caatinga biome. The most relevant variables to explain runoff initiation were total precipitation and maximum 60-min rainfall intensity (I-60). Runoff always occurred when rainfall surpassed 31mm, but it never occurred for rainfall below 14mm or for I-60 below 12mmh(-1). The fact that the duration of the critical intensity is similar to the basin concentration time (65min) and that the infiltration threshold value approaches the river-bank saturated hydraulic conductivity support the assumption that Hortonian runoff prevails. However, none of the analysed variables (total or precedent precipitation, soil moisture content, rainfall intensities or rainfall duration) has been able to explain the runoff initiation in all monitored events: the best criteria, e.g. failed to explain 27\% of the events. It is possible that surface-flow initiation in the Caatinga biome is strongly influenced by the root-system dynamics, which changes macro-porosity status and, therefore, initial abstraction. Copyright (c) 2016 John Wiley \& Sons, Ltd.},
  language  = {en}
}
@article{KaiserWehrhanWerneretal.2012,
  author    = {Kaiser, Thomas and Wehrhan, Marc and Werner, Armin and Sommer, Michael},
  title     = {Regionalizing ecological moisture levels and groundwater levels in grassland areas using thermal remote sensing},
  series = {Grassland science},
  volume    = {58},
  journal   = {Grassland science},
  number    = {1},
  publisher = {Wiley-Blackwell},
  address   = {Malden},
  issn      = {1744-6961},
  doi       = {10.1111/j.1744-697X.2011.00240.x},
  pages     = {42 -- 52},
  year      = {2012},
  abstract  = {Site-specific soil moisture and groundwater levels are key input parameters for ecological modeling. Obtaining such information in a comprehensive manner is difficult for large regions. We studied a floodplain region in the Federal State of Brandenburg, Germany, to examine the degree to which the average depth of groundwater tables can be derived from surface temperatures obtained by the ASTER radiospectrometer (spatial resolution of 90 m per pixel). A floristic ecological indicator representing the site-specific moisture level was applied to develop a proxy between the thermal satellite data and groundwater table depth. The use of spring scenes (late April to early May) from 2 years proved to be well suited for minimizing the effects of weather and land use. Vegetation surveys along transects that were 2 m wide across the pixel diagonals allowed for the calculation of average ecological moisture values of pixel-sites by applying Ellenberg-numbers. These values were used to calibrate the satellite data locally. There was a close relationship between surface temperature and the average ecological moisture value (R2 = 0.73). Average ecological moisture values were highly indicative of the average groundwater levels during a 7-year measurement series (R2 = 0.93). Satellite-supported thermal data from spring were suitable for estimating the average groundwater levels of low-lying grasslands on a larger scale. Ecological moisture values from the transect surveys effectively allowed the incorporation of relief heterogeneity within the thermal grid and the establishment of the correlation between thermal data and average groundwater table depth. Regression functions were used to produce a map of groundwater levels at the study site.},
  language  = {en}
}
@misc{GraeffZeheBlumeetal.2012,
  author    = {Graeff, T. and Zehe, E. and Blume, T. and Francke, Till and Schroeder, B.},
  title     = {Predicting event response in a nested catchment with generalized linear models and a distributed watershed model},
  series = {HYDROLOGICAL PROCESSES},
  volume    = {26},
  journal   = {HYDROLOGICAL PROCESSES},
  number    = {24},
  publisher = {WILEY-BLACKWELL},
  address   = {HOBOKEN},
  issn      = {0885-6087},
  doi       = {10.1002/hyp.8463},
  pages     = {3749 -- 3769},
  year      = {2012},
  abstract  = {This study focuses on the prediction of event-based runoff coefficients (an important descriptor of flood events) for nested catchments up to an area of 50?km(2) in the Eastern Ore Mountains. The four main objectives of the study are (i) the prediction of runoff coefficients with the statistical method of generalized linear models, (ii) the comparison of the results of the linear models with estimates of a distributed conceptual model, (iii) the comparison of the dynamics of observed soil moisture and simulated saturation deficit of the hydrological model and (iv) the analysis of the relationship between runoff coefficient and observed and simulated wetness. Different predictor variables were selected to describe the runoff coefficient and were differentiated into variables describing the catchment\’s antecedent wetness and meteorological forcing. The best statistical model was estimated in a stepwise approach on the basis of hierarchical partitioning, an exhaustive search algorithm and model validation with jackknifing. We then applied the rainfall runoff model WaSiM ETH to predict the runoff processes for the two larger catchments. Locally measured small-scale soil moisture (acquired at a scale of four to five magnitudes smaller than the catchment) was identified as one of the key predictor variables for the estimation of the runoff coefficient with the general linear model. It was found that the relationship betweenobserved and simulated (using WaSiM ETH) wetness is strongly hysteretic. The runoff coefficients derived from the rainfall runoff simulations systematically underestimate the observed values. Copyright (C) 2012 John Wiley \& Sons, Ltd.},
  language  = {en}
}
@article{SchroenOswaldZachariasetal.2021,
  author    = {Schr{\"o}n, Martin and Oswald, Sascha and Zacharias, Steffen and Kasner, Mandy and Dietrich, Peter and Attinger, Sabine},
  title     = {Neutrons on rails},
  series = {Geophysical research letters : GRL / American Geophysical Union},
  volume    = {48},
  journal   = {Geophysical research letters : GRL / American Geophysical Union},
  number    = {24},
  publisher = {Wiley},
  address   = {Hoboken, NJ},
  issn      = {0094-8276},
  doi       = {10.1029/2021GL093924},
  pages     = {10},
  year      = {2021},
  abstract  = {Large-scale measurements of the spatial distribution of water content in soils and snow are challenging for state-of-the-art hydrogeophysical methods. Cosmic-ray neutron sensing (CRNS) is a noninvasive technology that has the potential to bridge the scale gap between conventional in situ sensors and remote sensing products in both, horizontal and vertical domains. In this study, we explore the feasibility and potential of estimating water content in soils and snow with neutron detectors in moving trains. Theoretical considerations quantify the stochastic measurement uncertainty as a function of water content, altitude, resolution, and detector efficiency. Numerical experiments demonstrate that the sensitivity of measured water content is almost unperturbed by train materials. Finally, three distinct real-world experiments provide a proof of concept on short and long-range tracks. With our results a transregional observational soil moisture product becomes a realistic vision within the next years.},
  language  = {en}
}
@misc{WagnerOswaldFrick2018,
  author    = {Wagner, Kathrin and Oswald, Sascha and Frick, Annett},
  title     = {Multitemporal soil moisture monitoring by use of optical remote sensing data in a dike relocation area},
  series = {Remote Sensing for Agriculture, Ecosystems, and Hydrology XX},
  volume    = {10783},
  journal   = {Remote Sensing for Agriculture, Ecosystems, and Hydrology XX},
  publisher = {SPIE-INT Soc Optical Engineering},
  address   = {Bellingham},
  isbn      = {978-1-5106-2150-3},
  issn      = {0277-786X},
  doi       = {10.1117/12.2325319},
  pages     = {5},
  year      = {2018},
  abstract  = {The nature restoration project 'Lenzener Elbtalaue', realised from 2002 to 2011 at the river Elbe, included the first large scale dike relocation in Germany (420 ha). Its aim was to initiate the development of endangered natural wetland habitats and processes, accompanied by greater biodiversity in the former grassland dominated area. The monitoring of spatial and temporal variations of soil moisture in this dike relocation area is therefore particularly important for estimating the restoration success. The topsoil moisture monitoring from 1990 to 2017 is based on the Soil Moisture Index (SMI)1 derived with the triangle method2 by use of optical remotely sensed data: land surface temperature and Normalized Differnce Vegetation Index are calculated from Landsat 4/5/7/8 data and atmospheric corrected by use of MODIS data. Spatial and temporal soil moisture variations in the restored area of the dike relocation are compared to the agricultural and pasture area behind the new dike. Ground truth data in the dike relocation area was obtained from field measurements in October 2017 with a FDR device. Additionally, data from a TERENO soil moisture sensor network (SoilNet) and mobile cosmic ray neutron sensing (CRNS) rover measurements are compared to the results of the triangle method for a region in the Harz Mountains (Germany). The SMI time series illustrates, that the dike relocation area has become significantly wetter between 1990 and 2017, due to restructuring measurements. Whereas the SMI of the dike hinterland reflects constant and drier conditions. An influence of climate is unlikely. However, validation of the dimensionless index with ground truth measurements is very difficult, mostly due to large differences in scale.},
  language  = {en}
}
@article{WeimarKoehliBudachetal.2020,
  author    = {Weimar, Jannis and K{\"o}hli, Markus and Budach, Christian and Schmidt, Ulrich},
  title     = {Large-scale boron-lined neutron detection systems as a 3He alternative for Cosmic Ray Neutron Sensing},
  series = {Frontiers in water},
  volume    = {2},
  journal   = {Frontiers in water},
  publisher = {Frontiers Media},
  address   = {Lausanne},
  issn      = {2624-9375},
  doi       = {10.3389/frwa.2020.00016},
  pages     = {17},
  year      = {2020},
  abstract  = {Cosmic-Ray neutron sensors are widely used to determine soil moisture on the hectare scale. Precise measurements, especially in the case of mobile application, demand for neutron detectors with high counting rates and high signal-to-noise ratios. For a long time Cosmic Ray Neutron Sensing (CRNS) instruments have relied on He-3 as an efficient neutron converter. Its ongoing scarcity demands for technological solutions using alternative converters, which are Li-6 and B-10. Recent developments lead to a modular neutron detector consisting of several B-10-lined proportional counter tubes, which feature high counting rates via its large surface area. The modularity allows for individual shieldings of different segments within the detector featuring the capability of gaining spectral information about the detected neutrons. This opens the possibility for active signal correction, especially useful when applied to mobile measurements, where the influence of constantly changing near-field to the overall signal should be corrected. Furthermore, the signal-to-noise ratio could be increased by combining pulse height and pulse length spectra to discriminate between neutrons and other environmental radiation. This novel detector therefore combines high-selective counting electronics with large-scale instrumentation technology.},
  language  = {en}
}
@article{SchroenRosolemKoehlietal.2018,
  author    = {Schr{\"o}n, Martin and Rosolem, Rafael and K{\"o}hli, Markus and Piussi, L. and Schr{\"o}ter, I. and Iwema, J. and K{\"o}gler, S. and Oswald, Sascha and Wollschl{\"a}ger, U. and Samaniego, Luis and Dietrich, Peter and Zacharias, Steffen},
  title     = {Cosmic-ray Neutron Rover Surveys of Field Soil Moisture and the Influence of Roads},
  series = {Water resources research},
  volume    = {54},
  journal   = {Water resources research},
  number    = {9},
  publisher = {American Geophysical Union},
  address   = {Washington},
  issn      = {0043-1397},
  doi       = {10.1029/2017WR021719},
  pages     = {6441 -- 6459},
  year      = {2018},
  abstract  = {Measurements of root-zone soil moisture across spatial scales of tens to thousands of meters have been a challenge for many decades. The mobile application of Cosmic Ray Neutron Sensing (CRNS) is a promising approach to measure field soil moisture noninvasively by surveying large regions with a ground-based vehicle. Recently, concerns have been raised about a potentially biasing influence of local structures and roads. We employed neutron transport simulations and dedicated experiments to quantify the influence of different road types on the CRNS measurement. We found that roads introduce a substantial bias in the CRNS estimation of field soil moisture compared to off-road scenarios. However, this effect becomes insignificant at distances beyond a few meters from the road. Neutron measurements on the road could overestimate the field value by up to 40 \% depending on road material, width, and the surrounding field water content. The bias could be largely removed with an analytical correction function that accounts for these parameters. Additionally, an empirical approach is proposed that can be used without prior knowledge of field soil moisture. Tests at different study sites demonstrated good agreement between road-effect corrected measurements and field soil moisture observations. However, if knowledge about the road characteristics is missing, measurements on the road could substantially reduce the accuracy of this method. Our results constitute a practical advancement of the mobile CRNS methodology, which is important for providing unbiased estimates of field-scale soil moisture to support applications in hydrology, remote sensing, and agriculture. Plain Language Summary Measurements of root-zone soil moisture across spatial scales of tens to thousands of meters have been a challenge for many decades. The mobile application of Cosmic Ray Neutron Sensing (CRNS) is a promising approach to measure field soil moisture noninvasively by surveying large regions with a ground-based vehicle. Recently, concerns have been raised about a potentially biasing influence of roads. We employed physics simulations and dedicated experiments to quantify the influence of different road types on the CRNS measurement. We found that the presence of roads biased the CRNS estimation of field soil moisture compared to nonroad scenarios. Neutron measurements could overestimate the field value by up to 40 \% depending on road material, width, surrounding field water content, and distance from the road. We proposed a correction function that successfully removed this bias and works even without prior knowledge of field soil moisture. Tests at different study sites demonstrated good agreement between corrected measurements and other field soil moisture observations. Our results constitute a practical advancement of the mobile CRNS methodology, which is important for providing unbiased estimates of field-scale soil moisture to support applications in hydrology, remote sensing, and agriculture.},
  language  = {en}
}
@article{MeisslFormayerKlebinderetal.2017,
  author    = {Meißl, Gertraud and Formayer, Herbert and Klebinder, Klaus and Kerl, Florian and Sch{\"o}berl, Friedrich and Geitner, Clemens and Markart, Gerhard and Leidinger, David and Bronstert, Axel},
  title     = {Climate change effects on hydrological system conditions influencing generation of storm runoff in small Alpine catchments},
  series = {Hydrological processes : an international journal},
  volume    = {31},
  journal   = {Hydrological processes : an international journal},
  number    = {6},
  publisher = {Wiley},
  address   = {New York},
  issn      = {0885-6087},
  doi       = {10.1002/hyp.11104},
  pages     = {1314 -- 1330},
  year      = {2017},
  abstract  = {Floods and debris flows in small Alpine torrent catchments (<10km(2)) arise from a combination of critical antecedent system state conditions and mostly convective precipitation events with high precipitation intensities. Thus, climate change may influence the magnitude-frequency relationship of extreme events twofold: by a modification of the occurrence probabilities of critical hydrological system conditions and by a change of event precipitation characteristics. Three small Alpine catchments in different altitudes in Western Austria (Ruggbach, Brixenbach and Langentalbach catchment) were investigated by both field experiments and process-based simulation. Rainfall-runoff model (HQsim) runs driven by localized climate scenarios (CNRM-RM4.5/ARPEGE, MPI-REMO/ECHAM5 and ICTP-RegCM3/ECHAM5) were used in order to estimate future frequencies of stormflow triggering system state conditions. According to the differing altitudes of the study catchments, two effects of climate change on the hydrological systems can be observed. On one hand, the seasonal system state conditions of medium altitude catchments are most strongly affected by air temperature-controlled processes such as the development of the winter snow cover as well as evapotranspiration. On the other hand, the unglaciated high-altitude catchment is less sensitive to climate change-induced shifts regarding days with critical antecedent soil moisture and desiccated litter layer due to its elevation-related small proportion of sensitive areas. For the period 2071-2100, the number of days with critical antecedent soil moisture content will be significantly reduced to about 60\% or even less in summer in all catchments. In contrast, the number of days with dried-out litter layers causing hydrophobic effects will increase by up to 8\%-11\% of the days in the two lower altitude catchments. The intensity analyses of heavy precipitation events indicate a clear increase in rain intensities of up to 10\%.},
  language  = {en}
}