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Simone Bircher - One of the best experts on this subject based on the ideXlab platform.

  • Passive L-band microwave remote sensing of organic Soil Surface Layers: a tower-based experiment
    Remote Sensing, 2018
    Co-Authors: François Jonard, Simone Bircher, Jean-pierre Wigneron, Lutz Weihermüller, François Demontoux, Stephen Razafindratsima, Harry Vereecken
    Abstract:

    Organic Soils play a key role in global warming because they store large amount of Soil carbon which might be degraded with changing Soil temperatures or Soil water contents. There is thus a strong need to monitor these Soils and, in particular, their hydrological characteristics using, for instance, space-borne L-band brightness temperature observations. However, there are still open issues with respect to Soil moisture retrieval techniques over organic Soils. In view of this, organic Soil blocks with their vegetation cover were collected from a heathland in the Skjern River catchment in western Denmark and then transported to a remote sensing field laboratory in Germany where their structure was reconstituted. The controlled conditions at this field laboratory made it possible to perform tower-based L-band radiometer measurements of the Soils over a period of two months. Brightness temperature data were inverted using a radiative transfer (RT) model for estimating the time variations in the Soil dielectric permittivity and the vegetation optical depth. In addition, the effective vegetation scattering albedo parameter of the RT model was retrieved based on a two-step inversion approach. The remote estimations of the dielectric permittivity were compared to in situ measurements. The results indicated that the radiometer-derived dielectric permittivities were significantly correlated with the in situ measurements, but their values were systematically lower compared to the in situ ones. This could be explained by the difference between the operating frequency of the L-band radiometer (1.4 GHz) and that of the in situ sensors (70 MHz). The effective vegetation scattering albedo parameter was found to be polarization dependent. While the scattering effect within the vegetation could be neglected at horizontal polarization, it was found to be important at vertical polarization. The vegetation optical depth estimated values over time oscillated between 0.10 and 0.19 with a mean value of 0.13. This study provides further insights into the characterization of the L-band brightness temperature signatures of organic Soil Surface Layers and, in particular, into the parametrization of the RT model for these specific Soils. Therefore, the results of this study are expected to improve the performance of space-borne remote sensing Soil moisture products over areas dominated by organic Soils.

  • l band relative permittivity of organic Soil Surface Layers a new dataset of resonant cavity measurements and model evaluation
    Remote Sensing, 2016
    Co-Authors: Simone Bircher, Elena Zakharova, Jean-pierre Wigneron, François Demontoux, Stephen Razafindratsima, M Drusch, Yann Kerr
    Abstract:

    Global Surface Soil moisture products are derived from passive L-band microwave satellite observations. The applied retrieval algorithms include dielectric models (relating Soil water content to relative permittivity) developed for mineral Soils. First efforts to generate equivalent models for areas where organic Surface Layers are present such as in the high-latitude regions have recently been undertaken. The objective of this study was to improve our still insufficient understanding of L-band emission of organic substrates in prospect of enhancing Soil moisture estimations in the high latitudes undergoing most rapid climatic changes. To this end, L-band relative permittivity measurements using a resonant cavity were carried out on a wide range of organic Surface layer types collected at different sites. This dataset was used to evaluate two already existing models for organic substrates. Some samples from underlying mineral Layers were considered for comparison. In agreement with theory the bulk relative permittivity measured in organic substrate was decreased due to an increased bound water fraction (where water molecules are rotationally hindered) compared to the measured mineral material and corresponding output of the dielectric model for mineral Soils used in satellite algorithms. No distinct differences in dielectric response were detected in the measurements from various organic layer types, suggesting a generally uniform L-band emission behavior. This made it possible to fit a simple empirical model to the data obtained from all collected organic samples. Outputs of the two existing models both based on only one organic Surface layer type were found to lie within the spread of our measured data, and in close proximity to the derived simple model. This general consensus strengthened confidence in the validity of all these models. The simple model should be suitable for satellite Soil moisture retrieval applications as it is calibrated on a wide range of organic substrate types and the entire wetness range, and does not require any auxiliary input that may be difficult to obtain globally. This renders it generically applicable wherever organic Surface Layers are present.

  • Soil moisture sensor calibration for organic Soil Surface Layers
    Geoscientific Instrumentation Methods and Data Systems Discussions, 2016
    Co-Authors: Simone Bircher, Elena Zakharova, Jean-pierre Wigneron, Mie Andreasen, Johanna Vuollet, Juho Vehviläinen, Kimmo Rautiainen, François Jonard, Lutz Weihermüller, Yann Kerr
    Abstract:

    This paper's objective is to present generic calibration functions for organic Surface Layers derived for the Soil moisture sensors Decagon ECH2O 5TE and Delta-T ThetaProbe ML2x, using material from northern regions, mainly from the Finnish Meteorological Institute's Arctic Research Center in Sodankylä and the study area of the Danish Center for Hydrology (HOBE). For the Decagon 5TE sensor such a function is currently not reported in the literature. Data were compared with measurements from underlying mineral Soils including laboratory and field measurements. Shrinkage and charring during drying were considered. For both sensors all field and lab data showed consistent trends. For mineral Layers with low Soil organic matter (SOM) content the validity of the manufacturer's calibrations was demonstrated. Deviating sensor outputs in organic and mineral horizons were identified. For the Decagon 5TE, apparent relative permittivities at a given moisture content decreased for increased SOM content, which was attributed to an increase of bound water in organic materials with large specific Surface areas compared to the studied mineral Soils. ThetaProbe measurements from organic horizons showed stronger nonlinearity in the sensor response and signal saturation in the high-level data. The derived calibration fit functions between sensor response and volumetric water content hold for samples spanning a wide range of humus types with differing SOM characteristics. This strengthens confidence in their validity under various conditions, rendering them highly suitable for large-scale applications in remote sensing and land Surface modeling studies. Agreement between independent Decagon 5TE and ThetaProbe time series from an organic Surface layer at the Sodankylä site was significantly improved when the here-proposed fit functions were used. Decagon 5TE data also well-reflected precipitation events. Thus, Decagon 5TE network data from organic Surface Layers at the Sodankylä and HOBE sites are based on the here-proposed natural log fit. The newly derived ThetaProbe fit functions should be used for hand-held applications only, but prove to be of value for the acquisition of instantaneous large-scale Soil moisture estimates.

Jean-pierre Wigneron - One of the best experts on this subject based on the ideXlab platform.

  • Passive L-band microwave remote sensing of organic Soil Surface Layers: a tower-based experiment
    Remote Sensing, 2018
    Co-Authors: François Jonard, Simone Bircher, Jean-pierre Wigneron, Lutz Weihermüller, François Demontoux, Stephen Razafindratsima, Harry Vereecken
    Abstract:

    Organic Soils play a key role in global warming because they store large amount of Soil carbon which might be degraded with changing Soil temperatures or Soil water contents. There is thus a strong need to monitor these Soils and, in particular, their hydrological characteristics using, for instance, space-borne L-band brightness temperature observations. However, there are still open issues with respect to Soil moisture retrieval techniques over organic Soils. In view of this, organic Soil blocks with their vegetation cover were collected from a heathland in the Skjern River catchment in western Denmark and then transported to a remote sensing field laboratory in Germany where their structure was reconstituted. The controlled conditions at this field laboratory made it possible to perform tower-based L-band radiometer measurements of the Soils over a period of two months. Brightness temperature data were inverted using a radiative transfer (RT) model for estimating the time variations in the Soil dielectric permittivity and the vegetation optical depth. In addition, the effective vegetation scattering albedo parameter of the RT model was retrieved based on a two-step inversion approach. The remote estimations of the dielectric permittivity were compared to in situ measurements. The results indicated that the radiometer-derived dielectric permittivities were significantly correlated with the in situ measurements, but their values were systematically lower compared to the in situ ones. This could be explained by the difference between the operating frequency of the L-band radiometer (1.4 GHz) and that of the in situ sensors (70 MHz). The effective vegetation scattering albedo parameter was found to be polarization dependent. While the scattering effect within the vegetation could be neglected at horizontal polarization, it was found to be important at vertical polarization. The vegetation optical depth estimated values over time oscillated between 0.10 and 0.19 with a mean value of 0.13. This study provides further insights into the characterization of the L-band brightness temperature signatures of organic Soil Surface Layers and, in particular, into the parametrization of the RT model for these specific Soils. Therefore, the results of this study are expected to improve the performance of space-borne remote sensing Soil moisture products over areas dominated by organic Soils.

  • l band relative permittivity of organic Soil Surface Layers a new dataset of resonant cavity measurements and model evaluation
    Remote Sensing, 2016
    Co-Authors: Simone Bircher, Elena Zakharova, Jean-pierre Wigneron, François Demontoux, Stephen Razafindratsima, M Drusch, Yann Kerr
    Abstract:

    Global Surface Soil moisture products are derived from passive L-band microwave satellite observations. The applied retrieval algorithms include dielectric models (relating Soil water content to relative permittivity) developed for mineral Soils. First efforts to generate equivalent models for areas where organic Surface Layers are present such as in the high-latitude regions have recently been undertaken. The objective of this study was to improve our still insufficient understanding of L-band emission of organic substrates in prospect of enhancing Soil moisture estimations in the high latitudes undergoing most rapid climatic changes. To this end, L-band relative permittivity measurements using a resonant cavity were carried out on a wide range of organic Surface layer types collected at different sites. This dataset was used to evaluate two already existing models for organic substrates. Some samples from underlying mineral Layers were considered for comparison. In agreement with theory the bulk relative permittivity measured in organic substrate was decreased due to an increased bound water fraction (where water molecules are rotationally hindered) compared to the measured mineral material and corresponding output of the dielectric model for mineral Soils used in satellite algorithms. No distinct differences in dielectric response were detected in the measurements from various organic layer types, suggesting a generally uniform L-band emission behavior. This made it possible to fit a simple empirical model to the data obtained from all collected organic samples. Outputs of the two existing models both based on only one organic Surface layer type were found to lie within the spread of our measured data, and in close proximity to the derived simple model. This general consensus strengthened confidence in the validity of all these models. The simple model should be suitable for satellite Soil moisture retrieval applications as it is calibrated on a wide range of organic substrate types and the entire wetness range, and does not require any auxiliary input that may be difficult to obtain globally. This renders it generically applicable wherever organic Surface Layers are present.

  • Soil moisture sensor calibration for organic Soil Surface Layers
    Geoscientific Instrumentation Methods and Data Systems Discussions, 2016
    Co-Authors: Simone Bircher, Elena Zakharova, Jean-pierre Wigneron, Mie Andreasen, Johanna Vuollet, Juho Vehviläinen, Kimmo Rautiainen, François Jonard, Lutz Weihermüller, Yann Kerr
    Abstract:

    This paper's objective is to present generic calibration functions for organic Surface Layers derived for the Soil moisture sensors Decagon ECH2O 5TE and Delta-T ThetaProbe ML2x, using material from northern regions, mainly from the Finnish Meteorological Institute's Arctic Research Center in Sodankylä and the study area of the Danish Center for Hydrology (HOBE). For the Decagon 5TE sensor such a function is currently not reported in the literature. Data were compared with measurements from underlying mineral Soils including laboratory and field measurements. Shrinkage and charring during drying were considered. For both sensors all field and lab data showed consistent trends. For mineral Layers with low Soil organic matter (SOM) content the validity of the manufacturer's calibrations was demonstrated. Deviating sensor outputs in organic and mineral horizons were identified. For the Decagon 5TE, apparent relative permittivities at a given moisture content decreased for increased SOM content, which was attributed to an increase of bound water in organic materials with large specific Surface areas compared to the studied mineral Soils. ThetaProbe measurements from organic horizons showed stronger nonlinearity in the sensor response and signal saturation in the high-level data. The derived calibration fit functions between sensor response and volumetric water content hold for samples spanning a wide range of humus types with differing SOM characteristics. This strengthens confidence in their validity under various conditions, rendering them highly suitable for large-scale applications in remote sensing and land Surface modeling studies. Agreement between independent Decagon 5TE and ThetaProbe time series from an organic Surface layer at the Sodankylä site was significantly improved when the here-proposed fit functions were used. Decagon 5TE data also well-reflected precipitation events. Thus, Decagon 5TE network data from organic Surface Layers at the Sodankylä and HOBE sites are based on the here-proposed natural log fit. The newly derived ThetaProbe fit functions should be used for hand-held applications only, but prove to be of value for the acquisition of instantaneous large-scale Soil moisture estimates.

Yann Kerr - One of the best experts on this subject based on the ideXlab platform.

  • l band relative permittivity of organic Soil Surface Layers a new dataset of resonant cavity measurements and model evaluation
    Remote Sensing, 2016
    Co-Authors: Simone Bircher, Elena Zakharova, Jean-pierre Wigneron, François Demontoux, Stephen Razafindratsima, M Drusch, Yann Kerr
    Abstract:

    Global Surface Soil moisture products are derived from passive L-band microwave satellite observations. The applied retrieval algorithms include dielectric models (relating Soil water content to relative permittivity) developed for mineral Soils. First efforts to generate equivalent models for areas where organic Surface Layers are present such as in the high-latitude regions have recently been undertaken. The objective of this study was to improve our still insufficient understanding of L-band emission of organic substrates in prospect of enhancing Soil moisture estimations in the high latitudes undergoing most rapid climatic changes. To this end, L-band relative permittivity measurements using a resonant cavity were carried out on a wide range of organic Surface layer types collected at different sites. This dataset was used to evaluate two already existing models for organic substrates. Some samples from underlying mineral Layers were considered for comparison. In agreement with theory the bulk relative permittivity measured in organic substrate was decreased due to an increased bound water fraction (where water molecules are rotationally hindered) compared to the measured mineral material and corresponding output of the dielectric model for mineral Soils used in satellite algorithms. No distinct differences in dielectric response were detected in the measurements from various organic layer types, suggesting a generally uniform L-band emission behavior. This made it possible to fit a simple empirical model to the data obtained from all collected organic samples. Outputs of the two existing models both based on only one organic Surface layer type were found to lie within the spread of our measured data, and in close proximity to the derived simple model. This general consensus strengthened confidence in the validity of all these models. The simple model should be suitable for satellite Soil moisture retrieval applications as it is calibrated on a wide range of organic substrate types and the entire wetness range, and does not require any auxiliary input that may be difficult to obtain globally. This renders it generically applicable wherever organic Surface Layers are present.

  • Soil moisture sensor calibration for organic Soil Surface Layers
    Geoscientific Instrumentation Methods and Data Systems Discussions, 2016
    Co-Authors: Simone Bircher, Elena Zakharova, Jean-pierre Wigneron, Mie Andreasen, Johanna Vuollet, Juho Vehviläinen, Kimmo Rautiainen, François Jonard, Lutz Weihermüller, Yann Kerr
    Abstract:

    This paper's objective is to present generic calibration functions for organic Surface Layers derived for the Soil moisture sensors Decagon ECH2O 5TE and Delta-T ThetaProbe ML2x, using material from northern regions, mainly from the Finnish Meteorological Institute's Arctic Research Center in Sodankylä and the study area of the Danish Center for Hydrology (HOBE). For the Decagon 5TE sensor such a function is currently not reported in the literature. Data were compared with measurements from underlying mineral Soils including laboratory and field measurements. Shrinkage and charring during drying were considered. For both sensors all field and lab data showed consistent trends. For mineral Layers with low Soil organic matter (SOM) content the validity of the manufacturer's calibrations was demonstrated. Deviating sensor outputs in organic and mineral horizons were identified. For the Decagon 5TE, apparent relative permittivities at a given moisture content decreased for increased SOM content, which was attributed to an increase of bound water in organic materials with large specific Surface areas compared to the studied mineral Soils. ThetaProbe measurements from organic horizons showed stronger nonlinearity in the sensor response and signal saturation in the high-level data. The derived calibration fit functions between sensor response and volumetric water content hold for samples spanning a wide range of humus types with differing SOM characteristics. This strengthens confidence in their validity under various conditions, rendering them highly suitable for large-scale applications in remote sensing and land Surface modeling studies. Agreement between independent Decagon 5TE and ThetaProbe time series from an organic Surface layer at the Sodankylä site was significantly improved when the here-proposed fit functions were used. Decagon 5TE data also well-reflected precipitation events. Thus, Decagon 5TE network data from organic Surface Layers at the Sodankylä and HOBE sites are based on the here-proposed natural log fit. The newly derived ThetaProbe fit functions should be used for hand-held applications only, but prove to be of value for the acquisition of instantaneous large-scale Soil moisture estimates.

Stephen Razafindratsima - One of the best experts on this subject based on the ideXlab platform.

  • Passive L-band microwave remote sensing of organic Soil Surface Layers: a tower-based experiment
    Remote Sensing, 2018
    Co-Authors: François Jonard, Simone Bircher, Jean-pierre Wigneron, Lutz Weihermüller, François Demontoux, Stephen Razafindratsima, Harry Vereecken
    Abstract:

    Organic Soils play a key role in global warming because they store large amount of Soil carbon which might be degraded with changing Soil temperatures or Soil water contents. There is thus a strong need to monitor these Soils and, in particular, their hydrological characteristics using, for instance, space-borne L-band brightness temperature observations. However, there are still open issues with respect to Soil moisture retrieval techniques over organic Soils. In view of this, organic Soil blocks with their vegetation cover were collected from a heathland in the Skjern River catchment in western Denmark and then transported to a remote sensing field laboratory in Germany where their structure was reconstituted. The controlled conditions at this field laboratory made it possible to perform tower-based L-band radiometer measurements of the Soils over a period of two months. Brightness temperature data were inverted using a radiative transfer (RT) model for estimating the time variations in the Soil dielectric permittivity and the vegetation optical depth. In addition, the effective vegetation scattering albedo parameter of the RT model was retrieved based on a two-step inversion approach. The remote estimations of the dielectric permittivity were compared to in situ measurements. The results indicated that the radiometer-derived dielectric permittivities were significantly correlated with the in situ measurements, but their values were systematically lower compared to the in situ ones. This could be explained by the difference between the operating frequency of the L-band radiometer (1.4 GHz) and that of the in situ sensors (70 MHz). The effective vegetation scattering albedo parameter was found to be polarization dependent. While the scattering effect within the vegetation could be neglected at horizontal polarization, it was found to be important at vertical polarization. The vegetation optical depth estimated values over time oscillated between 0.10 and 0.19 with a mean value of 0.13. This study provides further insights into the characterization of the L-band brightness temperature signatures of organic Soil Surface Layers and, in particular, into the parametrization of the RT model for these specific Soils. Therefore, the results of this study are expected to improve the performance of space-borne remote sensing Soil moisture products over areas dominated by organic Soils.

  • l band relative permittivity of organic Soil Surface Layers a new dataset of resonant cavity measurements and model evaluation
    Remote Sensing, 2016
    Co-Authors: Simone Bircher, Elena Zakharova, Jean-pierre Wigneron, François Demontoux, Stephen Razafindratsima, M Drusch, Yann Kerr
    Abstract:

    Global Surface Soil moisture products are derived from passive L-band microwave satellite observations. The applied retrieval algorithms include dielectric models (relating Soil water content to relative permittivity) developed for mineral Soils. First efforts to generate equivalent models for areas where organic Surface Layers are present such as in the high-latitude regions have recently been undertaken. The objective of this study was to improve our still insufficient understanding of L-band emission of organic substrates in prospect of enhancing Soil moisture estimations in the high latitudes undergoing most rapid climatic changes. To this end, L-band relative permittivity measurements using a resonant cavity were carried out on a wide range of organic Surface layer types collected at different sites. This dataset was used to evaluate two already existing models for organic substrates. Some samples from underlying mineral Layers were considered for comparison. In agreement with theory the bulk relative permittivity measured in organic substrate was decreased due to an increased bound water fraction (where water molecules are rotationally hindered) compared to the measured mineral material and corresponding output of the dielectric model for mineral Soils used in satellite algorithms. No distinct differences in dielectric response were detected in the measurements from various organic layer types, suggesting a generally uniform L-band emission behavior. This made it possible to fit a simple empirical model to the data obtained from all collected organic samples. Outputs of the two existing models both based on only one organic Surface layer type were found to lie within the spread of our measured data, and in close proximity to the derived simple model. This general consensus strengthened confidence in the validity of all these models. The simple model should be suitable for satellite Soil moisture retrieval applications as it is calibrated on a wide range of organic substrate types and the entire wetness range, and does not require any auxiliary input that may be difficult to obtain globally. This renders it generically applicable wherever organic Surface Layers are present.

François Demontoux - One of the best experts on this subject based on the ideXlab platform.

  • Passive L-band microwave remote sensing of organic Soil Surface Layers: a tower-based experiment
    Remote Sensing, 2018
    Co-Authors: François Jonard, Simone Bircher, Jean-pierre Wigneron, Lutz Weihermüller, François Demontoux, Stephen Razafindratsima, Harry Vereecken
    Abstract:

    Organic Soils play a key role in global warming because they store large amount of Soil carbon which might be degraded with changing Soil temperatures or Soil water contents. There is thus a strong need to monitor these Soils and, in particular, their hydrological characteristics using, for instance, space-borne L-band brightness temperature observations. However, there are still open issues with respect to Soil moisture retrieval techniques over organic Soils. In view of this, organic Soil blocks with their vegetation cover were collected from a heathland in the Skjern River catchment in western Denmark and then transported to a remote sensing field laboratory in Germany where their structure was reconstituted. The controlled conditions at this field laboratory made it possible to perform tower-based L-band radiometer measurements of the Soils over a period of two months. Brightness temperature data were inverted using a radiative transfer (RT) model for estimating the time variations in the Soil dielectric permittivity and the vegetation optical depth. In addition, the effective vegetation scattering albedo parameter of the RT model was retrieved based on a two-step inversion approach. The remote estimations of the dielectric permittivity were compared to in situ measurements. The results indicated that the radiometer-derived dielectric permittivities were significantly correlated with the in situ measurements, but their values were systematically lower compared to the in situ ones. This could be explained by the difference between the operating frequency of the L-band radiometer (1.4 GHz) and that of the in situ sensors (70 MHz). The effective vegetation scattering albedo parameter was found to be polarization dependent. While the scattering effect within the vegetation could be neglected at horizontal polarization, it was found to be important at vertical polarization. The vegetation optical depth estimated values over time oscillated between 0.10 and 0.19 with a mean value of 0.13. This study provides further insights into the characterization of the L-band brightness temperature signatures of organic Soil Surface Layers and, in particular, into the parametrization of the RT model for these specific Soils. Therefore, the results of this study are expected to improve the performance of space-borne remote sensing Soil moisture products over areas dominated by organic Soils.

  • l band relative permittivity of organic Soil Surface Layers a new dataset of resonant cavity measurements and model evaluation
    Remote Sensing, 2016
    Co-Authors: Simone Bircher, Elena Zakharova, Jean-pierre Wigneron, François Demontoux, Stephen Razafindratsima, M Drusch, Yann Kerr
    Abstract:

    Global Surface Soil moisture products are derived from passive L-band microwave satellite observations. The applied retrieval algorithms include dielectric models (relating Soil water content to relative permittivity) developed for mineral Soils. First efforts to generate equivalent models for areas where organic Surface Layers are present such as in the high-latitude regions have recently been undertaken. The objective of this study was to improve our still insufficient understanding of L-band emission of organic substrates in prospect of enhancing Soil moisture estimations in the high latitudes undergoing most rapid climatic changes. To this end, L-band relative permittivity measurements using a resonant cavity were carried out on a wide range of organic Surface layer types collected at different sites. This dataset was used to evaluate two already existing models for organic substrates. Some samples from underlying mineral Layers were considered for comparison. In agreement with theory the bulk relative permittivity measured in organic substrate was decreased due to an increased bound water fraction (where water molecules are rotationally hindered) compared to the measured mineral material and corresponding output of the dielectric model for mineral Soils used in satellite algorithms. No distinct differences in dielectric response were detected in the measurements from various organic layer types, suggesting a generally uniform L-band emission behavior. This made it possible to fit a simple empirical model to the data obtained from all collected organic samples. Outputs of the two existing models both based on only one organic Surface layer type were found to lie within the spread of our measured data, and in close proximity to the derived simple model. This general consensus strengthened confidence in the validity of all these models. The simple model should be suitable for satellite Soil moisture retrieval applications as it is calibrated on a wide range of organic substrate types and the entire wetness range, and does not require any auxiliary input that may be difficult to obtain globally. This renders it generically applicable wherever organic Surface Layers are present.