Microwave Dielectric Behavior of Wet Soils

176 Pages·2005·0.695 MB·English

by  Jitendra Behari (auth.)

Microwave Dielectric Behavior of Wet Soils
Remote Sensing and Digital Image Processing
VOLUME 8
Series Editor:
Freek D. van der Meer, Department of Earth Systems Analysis, International Institute for
Geo-Information Science and Earth Observation (ITC), Enschede, The Netherlands
& Department of Geotechnology, Faculty of Civil Engineering and Geosciences,
Technical University Delft, The Netherlands
Editorial Advisory Board:
Michael Abrams, NASA Jet Propulsion Laboratory, Pasadena, CA, U.S.A.
Paul Curran, Department of Geography, University of Southampton, U.K.
Arnold Dekker, CSIRO, Land and Water Division, Canberra, Australia
Steven M. de Jong, Department of Physical Geography, Faculty of Geosciences,
Utrecht University, The Netherlands
Michael Schaepman, Centre for Geo-Information, Wageningen UR, The Netherlands
The titles published in this series are listed at the end of this volume.
MICROWAVE DIELECTRIC
BEHAVIOR OF WET SOILS
by
JITENDRA BEHARI
School of Environmental Sciences,
Jawaharlal Nehru University,
New Delhi, India
Springer
Anamaya
A.C.I.P. catalogue record for the book is available from the Library of Congress
ISBN 1-4020-3271-4 (HB)
ISBN 1-4020-3288-9 (e-book)
Copublished by Springer
233 Spring Street, New York 10013, USA
with Anamaya Publishers, New Delhi, India
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PREFACE
Soil moisture plays an important role in the runoff process, and its evaluation can be
used as a marker of flood risk or drought occurrence. The data is also required to
validate the soil moisture component in a variety of soil types of hydrologic models
before a possible flood event, and potentially improves the accuracy of their prediction.
Keeping the above in view, enormous efforts have gone into measurement of soil
moisture by in situ and remote sensing techniques using microwaves. The subject
still remains an important point of investigation for it depends upon a number of
parameters, for example, texture, topography and shows space and temporal variability.
The advantages of both passive and active remote sensing techniques are discussed
in detail.
The book begins with the basics of soil physics and the soil moisture. Soil moisture
measurement techniques presented are confined to microwave frequencies. A summary
of theoretical models and a mix-up of experimental and theoretical details is included
to offer a comparison. A special chapter is added on an upcoming technique of
synthetic aperture radar. The book finally concludes with a summary of recent trends
and techniques with a possible direction for future work.
The book is primarily aimed to benefit postgraduates and researchers in the area
of soil, agriculture physics and microwave remote sensing. The aim is to initiate
beginners in the subject. The author will consider his efforts rewarded if it succeeds
in such an endeavor.
J. BEHARI
LIST OF SYMBOLS
A Equivalent area of ‘synthesized beam’
syn
B System bandwidth
C Heat capacity
E Evaporation from the water surface
eβ Measured sensitivity of the two layer medium
e Emissivity of ground surface
surface
F(d) Visibility function
G Gain of receiving antenna
r
G Gain of transmission antenna
t
h Roughness parameter
K Boltzman’s constant
k d Optical thickness
e
lε Sample length
m Percentage of volumetric field capacity
f
m Gravimetric moisture content
g
m Mass of dry soil
s
m Mass of wet soil
st
m Transition moisture
t
m Volumetric water content (Soil moisture)
v
m Relative saturation
vr
m Saturated value
vs
P Total porosity of the soil
P Pore volume filled with air
a
P Penetration depth
d
P Power transmitted by the sensor
t
R(θ) Surface roughness
rg Reflectivity of the ground
β
r2 Correlation coefficient
R Polarized surface reflectivity
p
R Distance between radar and target
t
T Temperature of the vegetation
v
T Average temperature of the atmosphere
atm
T Brightness temperature
B
V Soil reflectivity
soil
viii LIST OF SYMBOLS
W Day length
W0 Observed soil moisture
W Wilting coefficient
p
W Transition point
t
Y Characteristic admittance of the probe
t
Z Characteristic impedance of transmission line
0
ρ Bulk density of soil
b
ε′ Real part of complex permittivity (dielectric constant)
ε″ Imaginary part of complex permittivity (dielectric constant)
ε′′ Conductivity loss
σ
ε′′ Total dielectric loss
t
ε Dielectric constant
Γ Transmissivity of the vegetation layer
t
β Empirical constant
φ Metric potential
m
δ Skin depth
D
ρ Particle density
r
τ Relaxation time
ω Angular frequency (2π f)
α Spread in relaxation
ε Permittivity of free space
0
λ Wavelength
µ Permeability of the medium
r
Γ Reflection coefficient
σ Ionic conductivity (mos/cm)
σ0 Backscattering coefficient
σ Zero frequency electrical conductivity
dc
θ Soil moisture content
θ Depth integrated vegetation/water content
veg
ϕ Phase constant
γsur Surface scattering
αβ
γg Bistatic scattering coefficient of the ground
α
CONTENTS
Preface v
List of Symbols vii
1. Physical Properties of Soil 1
Introduction 1
Drainage 2
Physical Properties of Mineral Soils 3
Soil Texture Classes 3
Inorganic Constituents in Soils 5
Particle Density of Mineral Soils 6
Structure of Mineral Soils 6
Soil Organic Composition 6
Bulk Density 7
Pore Space 7
Soil Temperature 8
Thermal Infrared Surface Temperatures 8
Soil Water Characteristics 9
Water Retention 10
Parameters Related to Soil Moisture Retention Under Field
Conditions 10
Computations of Soil Parameters 12
Soil Thermal Resistivity 13
Dry (Single-phase) Soils 13
Moist (Single-phase) Soils 13
Soil Air Characteristics 14
Clay and Humus 14
Surface Roughness 14
Roughness Estimation 15
Penetration Depth 16
Equivalent Soil Moisture 18
Emissivity of a Soil Layer 19
Microwave Brightness Temperature 20
Microwave Emission Model 20
x CONTENTS
2. Dielectric Behavior of Soil 22
Soil Moisture 22
Agriculture Applications 23
Soil Moisture Parameters 24
Soil Moisture Measurements 26
Visible and Infrared (0.3-3 µm) Electromagnetic Spectrum 26
Thermal Infrared Method 26
Microwaves 27
Physical Basis of Soil Moisture Measurement Using
Microwaves 28
Dielectric Behavior of Wet Soils 28
Bound Water Layer 29
Bulk Density Effects 33
Moisture, Texture and Frequency Dependence 33
Soil Textural Composition 33
Salinity Dependence 35
Temperature Dependence 37
Special Class of Soil 38
Vertisol 38
Density Effects 38
Dielectric Behavior of Swelling Clay Soils 38
3. Measurement of Soil Water Content 41
Measuring Methods 41
Microwave Response to Soil Moisture 41
Importance of Dielectric Constant Measurements: Theoretical
background 42
Importance of Microwaves in Soil Moisture Content 42
Microwave Based Experimental Techniques 43
Free Space Transmission Technique 43
Cavity Perturbation Method 44
Transmission Technique in Waveguides/Coaxial Lines 45
The Two Point Method 45
Network Analyzer in Reflection Measurements: Theoretical
background 46
Reflection Techniques in Coaxial Lines/Waveguides 48
Single-Horn Reflectometry Method: Theory and Description 49
Height Adjusting Setup Description 50
Limitations 51
The Coaxial Cable Method 52
Limitations 54
Precautions 54
Capacitance Probe (CP) 55
Microstrip Ring Resonator 55
Time Domain Reflectometry (TDR) 56
CONTENTS xi
Ground Penetrating Radar (GPR) 59
Measurements 60
Lysimeter 62
Comparison of Various Techniques 63
Conclusions 65
4. Microwave Remote Sensing Techniques in
Soil Moisture Estimation 66
Introduction 66
Radiant Energy and Flux 67
Basis of Microwave Remote Sensing 67
Passive Microwave Remote Sensing 69
Microwave Radiometers 70
Active Microwave Remote Sensing 74
Principle 74
Scatterometers 74
S- and L-Band Microwave Radiometer (SLMR) System 75
Theoretical Basis 77
Description of Scatterometer 79
Applications of Scatterometric Studies 79
Crop Covered Soil 81
System Parameters Affecting Microwave Signature 81
Frequency 81
Incident Angle 82
Polarization 82
Combination of System Parameters 83
Target Parameters Influencing Microwave Signatures 83
Effect of Roughness and Soil Texture 83
Effect of Vegetation 84
Canopy Attenuation 86
Vegetation Cover and Its Effect on Soil Moisture 87
Fresnel Model 87
Active and Passive Microwave Remote Sensing:
Comparison and a Relation 88
5. Dielectric Constant of Soil 92
Experimental Results 92
Prediction of e Using Calibration Procedures 92
Volumetric Soil Moisture Using Backscattering Data 93
Data Obtained Using Network Analyzer Technique 93
General Observations 97
Frequency 98
Finger Printing of Soil Texture with Moisture 99
In Situ Methods 103
Bound Water Problem in Relation to Experimental Data 103