Presentation on theme: "Measuring soil hydrological properties in different climatic and pedological conditions Marco Bittelli a, Markus Flury b, Paola Rossi Pisa a, Kurt Roth."— Presentation transcript:
Measuring soil hydrological properties in different climatic and pedological conditions Marco Bittelli a, Markus Flury b, Paola Rossi Pisa a, Kurt Roth c and Fiorenzo Salvatorelli a a Department of Agro-Environmental Science and Technology, University of Bologna, Italy. B Department of Crop and Soil Sciences, Washington State University, Pullman, WA, USA. c Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany.
Also thank to: l Gaylon Campbell l Vittorio Marletto l Franco Zinoni l Gernot Kasper l Andrea Pasquali l William Pratizzoli l Francesca Ventura
Soil Water Content l It controls the partitioning of radiation into sensible and latent heat l It couples the soil compartment to the atmosphere, in the hydrological cycle l It determines the partition of precipitation into runoff and infiltration l It determines soil solute transport (breakthrough curve)
Measurements at different scales l Point Scale (Gravimetry, Gypsum blocks, Neutron Probes, FDR, TDR and other). l Field Scale (Ground Penetrating Radar, Electrical Resistivity). l Regional Scale (Airborne Microwave Radiometry) l Global Scale (Satellite Passive Microwave Radiometry- Satellite Aqua)
Point Scale 1) Measurement in the Arctic 2) Measurement in the Italian Apennines 3) Measurement in the Italian Po valley
(1) ARCTIC: (1) ARCTIC: Liquid water and ice content in frozen porous media l Permafrost covers about one fifth of global land areas. It is a relevant terrestrial system because it plays an important role in earth surface temperature and into the calibration of climate models. l Soil freeze-thaw status influence plant growth, carbon exchange between the land and the atmosphere and surface and subsurface hydrology.
Permafrost studies Experimental station: - Weather Station - Soil temperature - Soil heat flux Liquid Water and Ice Content ?
Experimental Station (Svalbard) From: Ippisch, O., 2001: Coupled Transport in Natural Porous Media. Ph.D. Dissertation, University of Heidelberg, Germany
Example of the problem : 3 phase system = soil minerals = liquid water = ice = liquid water = soil minerals + ice EM field TDR Object Measurement w w i s i+s
Dielectric permittivity and relaxation of polar molecules (H 2 O) ++ + ++ + --- - + H2OH2O 0.01 0.1110100 Frequency (GHz) Dielectric permittivity 20 40 60 100 80 25 C = - i
Hypothesis l Ice undergoes relaxation at lower frequency (1 to 10 kHz), compared to liquid water. l Ice permittivity at low frequency is higher than at higher frequency (relaxation). l By measuring bulk dielectric permittivity at two different frequencies we can detect the ice dielectric fingerprint
Experimental setup (Kirchoff Institute of Physics, Heidelberg, Germany)
Results: dielectric Permittivity vs. Temperature
Results: Ice and Liquid Water Content Bittelli M., M. Flury and K. Roth, Use of Dielectric Spectroscopy to Estimate Ice Content in Frozen Porous Media. Water Resources Research, Vol. 40, W04212, doi:10.129/2003WR002343.
(2) APENNINES: (2) APENNINES: Liquid water content in Clay deposits l The Italian Apennine mountain chain is characterized by chaotic undifferentiated clay deposits. l Polarization and high dielectric conductivity in samples with high clay content causes dispersion of the electromagnetic wave energy and therefore could prevent measurement. l Technical and theoretical issues needs to be considered to successfully measure soil water content in these conditions.
Effect of high electrical conductivity on the TDR waveform
What to do 1) Reduction of the cable length 2) Reduction of the probe length 3) Covering the probe with plastic material 4) Frequency analysis via Fourier Transformation and separation of the real and imaginary component
(3) PO VALLEY: (3) PO VALLEY: Liquid water content in Alluvial Sand Deposits l The Italian Po Valley is often characterized by Alluvial deposits (conglomerates, gravel, sand) l In these conditions, dielectric conductivity is usually low because sand have low specific surface area and low ions contents. l If the area is under intense agricultural activities, where fertilizations are performed, high electrical conductivity can be due to high soil ionic concentration.
Conclusions and future work l TDR is becoming an increasingly utilized methodologies for soil water content measurement. l Its popularity is due to several reasons including time continuous data acquisition, precision, low cost, no risk for the operator. l Knowledge of the dielectric response of the material under investigation is needed, especially when operating on highly conductive material. l Soil Water Content studies at different scales are needed to elucidate the scale dependent features of these methodologies and provide input data to regional and global scale models.