27
Advanced Ground-Penetrating Radar for Soil Moisture Retrieval
a high spatial resolution at the field scale due to its rapidity and to the air-launched
configuration of the antenna. The soil moisture measurements were found to be
highly accurate and precise when comparing with the ground-truth measurements
and repeating the acquisition. The relatively large footprint of the GPR antenna
allows for integrating the soil moisture measurement at a larger support scale than
invasive sensors. When compared to commonly used ground-wave analysis based
on on-ground GPR, the observed differences were mainly attributed to the different depths of characterization. The off-ground GPR system resulted in similar soil
moisture maps compared to ground-based radiometry, whereas the latter technique
required ground-truth measurements of soil moisture for calibration with respect
to the surface roughness characterization. The large frequency bandwidth at which
the GPR operates allowed for maximizing the information retrieval capabilities
and, especially, to characterize a two-layered or continuously varying moisture
profile. The off-ground GPR was also used for time-lapse measurements of soil
moisture that were interpreted according to meteorological conditions. Finally,
time-lapse measurements over a field allowed for revealing the temporal stability of soil moisture patterns. This tool is promising for studying the spatiotemporal variability of soil moisture at the field scale, validation of remote sensing of
soil moisture products, improvement of hydrologic modeling through data assimilation, and precision agriculture and irrigation applications. In particular, high-spatial-resolution GPR acquisitions may be combined with high-temporal-resolution
grounded sensor networks for an unprecedented spatiotemporal characterization of
soil moisture patterns.
ACKNOWLEDGMENTS
This work was supported by the Université Catholique de Louvain (Belgium),
Forchungszentrum Jülich GmbH (Germany), Delft University of Technology (The
Netherlands), the Belgian Science Policy Office in the frame of the Stereo II
Programme—Project SR/00/100 (HYDRASENS), the DIGISOIL Project financed
by the European Commission under the 7th Framework Programme for Research
and Technological Development, Area “Environment,” Activity 6.3 “Environmental
Technologies,” the German Research Foundation (DFG) in the frame of Transregional
Collaborative Research Centre 32, and the Fonds de la Recherche Scientifique
(FNRS; Belgium).
REFERENCES
Alumbaugh, D., Chang, P., Paprocki, L., Brainard, J., Glass, R. J., and Rautman, C. A.
(2002). Estimating moisture contents in the vadose zone using cross-borehole ground
penetrating radar: A study of accuracy and repeatability. Water Resources Research,
38, 1309.
Benedetto, A. (2010). Water content evaluation in unsaturated soil using GPR signal analysis
in the frequency domain. Journal of Applied Geophysics, 71, 26–35.
Binley, A., Cassiani, G., Middleton, R., and Winship, P. (2002). Vadose zone flow model parameterisation using cross-borehole radar and resistivity imaging. Journal of Hydrology,
267, 147–159.
Advanced Ground-Penetrating Radar for Soil Moisture Retrieval
a high spatial resolution at the field scale due to its rapidity and to the air-launched
configuration of the antenna. The soil moisture measurements were found to be
highly accurate and precise when comparing with the ground-truth measurements
and repeating the acquisition. The relatively large footprint of the GPR antenna
allows for integrating the soil moisture measurement at a larger support scale than
invasive sensors. When compared to commonly used ground-wave analysis based
on on-ground GPR, the observed differences were mainly attributed to the different depths of characterization. The off-ground GPR system resulted in similar soil
moisture maps compared to ground-based radiometry, whereas the latter technique
required ground-truth measurements of soil moisture for calibration with respect
to the surface roughness characterization. The large frequency bandwidth at which
the GPR operates allowed for maximizing the information retrieval capabilities
and, especially, to characterize a two-layered or continuously varying moisture
profile. The off-ground GPR was also used for time-lapse measurements of soil
moisture that were interpreted according to meteorological conditions. Finally,
time-lapse measurements over a field allowed for revealing the temporal stability of soil moisture patterns. This tool is promising for studying the spatiotemporal variability of soil moisture at the field scale, validation of remote sensing of
soil moisture products, improvement of hydrologic modeling through data assimilation, and precision agriculture and irrigation applications. In particular, high-spatial-resolution GPR acquisitions may be combined with high-temporal-resolution
grounded sensor networks for an unprecedented spatiotemporal characterization of
soil moisture patterns.
ACKNOWLEDGMENTS
This work was supported by the Université Catholique de Louvain (Belgium),
Forchungszentrum Jülich GmbH (Germany), Delft University of Technology (The
Netherlands), the Belgian Science Policy Office in the frame of the Stereo II
Programme—Project SR/00/100 (HYDRASENS), the DIGISOIL Project financed
by the European Commission under the 7th Framework Programme for Research
and Technological Development, Area “Environment,” Activity 6.3 “Environmental
Technologies,” the German Research Foundation (DFG) in the frame of Transregional
Collaborative Research Centre 32, and the Fonds de la Recherche Scientifique
(FNRS; Belgium).
REFERENCES
Alumbaugh, D., Chang, P., Paprocki, L., Brainard, J., Glass, R. J., and Rautman, C. A.
(2002). Estimating moisture contents in the vadose zone using cross-borehole ground
penetrating radar: A study of accuracy and repeatability. Water Resources Research,
38, 1309.
Benedetto, A. (2010). Water content evaluation in unsaturated soil using GPR signal analysis
in the frequency domain. Journal of Applied Geophysics, 71, 26–35.
Binley, A., Cassiani, G., Middleton, R., and Winship, P. (2002). Vadose zone flow model parameterisation using cross-borehole radar and resistivity imaging. Journal of Hydrology,
267, 147–159.