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Measuring soil hydrological properties in different climatic and pedological conditions Marco...
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Transcript of Measuring soil hydrological properties in different climatic and pedological conditions Marco...
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:
Gaylon Campbell Vittorio Marletto Franco Zinoni Gernot Kasper Andrea Pasquali William Pratizzoli Francesca Ventura
Soil Water Content
It controls the partitioning of radiation into sensible and latent heat
It couples the soil compartment to the atmosphere, in the hydrological cycle
It determines the partition of precipitation into runoff and infiltration
It determines soil solute transport (breakthrough curve)
Measurements at different scales
Point Scale (Gravimetry, Gypsum blocks, Neutron Probes, FDR, TDR and other).
Field Scale (Ground Penetrating Radar, Electrical Resistivity).
Regional Scale (Airborne Microwave Radiometry)
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
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.
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
Soil
Example of the problem : 3 phase system
= soil minerals
= liquid water
= ice
= liquid water
= soil minerals + ice
EM field
TDR
“ObjectMeasurement”
w
w
i
s
i+s
Dielectric permittivity and relaxation of polarmolecules (H2O)
+ ++ + ++
- --
-
+
H2O
0.01 0.1 1 10 100
Frequency (GHz)
Die
lect
ric
pe
rmitt
ivity
20
40
60
100
80
25 C
= ’- i ’’
Hypothesis
Ice undergoes relaxation at lower frequency (1 to 10 kHz), compared to liquid water.
Ice permittivity at low frequency is higher than at higher frequency (relaxation).
By measuring bulk dielectric permittivity at two different frequencies we can detect the ice dielectric
fingerprint
Measured Ice permittivity
Theory : dielectric mixing model
1991) al., et Roth particle, soil of ondistributi random0.5( parameter lgeometrica
porosity
content ice volumetric
content air volumetric
content waterliquid volumetric
kHz) 100~ of f at 3.2 kHz; 100 f 0 for 4-(100ty permittivi dielectric ice
10)-(3ty permittivi dielectric mineralsdry
(1.005)ty permittivi dielectric air
85)-(75ty permittivi dielectric water
typermittivi dielectric bulk
i
a
w
i
s
a
w
b
Tf
Tf
Tf
Tf
Tf
),(
),(
),(
),(
),(
Theory: system of equations
Solution
,)(
)(
1,1,
2,2,,
sa
sasa
,)(
)(
1,1,
2,2,,
ai
aiai
,)(
)(
1,1,
2,2,,
al
alal
)(
)(
1,1,
2,2,
,si
si
si
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
The Italian Apennine mountain chain is characterized by chaotic undifferentiated clay deposits.
Polarization and high dielectric conductivity in samples with high clay content causes dispersion of the electromagnetic wave energy and therefore could prevent measurement.
Technical and theoretical issues needs to be considered to successfully measure soil water content in these conditions.
Aqua Modis
Experimental site
TDR probe Campbell CS610
Effect of high electrical conductivity on the TDR waveform
What to do
c
L2st
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
The Italian Po Valley is often characterized by Alluvial deposits (conglomerates, gravel, sand)
In these conditions, dielectric conductivity is usually low because sand have low specific surface area and low ions contents.
If the area is under intense agricultural activities, where fertilizations are performed, high electrical conductivity can be due to high soil ionic concentration.
Soil Profile
Paleo A horizon
TDR installation
sand
TDR 100, CR10X and battery charged by a solar panel
Conclusions and future work
TDR is becoming an increasingly utilized methodologies for soil water content measurement.
Its popularity is due to several reasons including time continuous data acquisition, precision, low cost, no risk for
the operator. Knowledge of the dielectric response of the material under
investigation is needed, especially when operating on highly conductive material.
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.
Thank you for your attention