remote sensing and soil thermal properties: eric russell 4/9/2010 agron 577: soil physics...
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Remote Sensing and Soil Thermal Properties:
Eric Russell4/9/2010
Agron 577: Soil Physics
Conductivity, Heat Capacity, and Electromagnetics! OH MY!
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Outline
• What is remote sensing?– Microwave remote sensing
• Very basic electromagnetics– Blackbody radiation, Wien’s law, Stefan-Boltzmann
law, brightness temperature• Soil thermal properties • Combining the previous two (the OH MY! part)• Figures
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What is remote sensing?
• Taking measurements from a place when not being in physical contact of that place.
• Satellites, MRI’s, IR thermometers, RADAR, LiDAR, camera
– For this presentation: microwaves
• Utilizes the electromagnetic spectrum (EM)
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EM Spectrum
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Base Electromagnetic equations
• Maxwell’s equations – Set of equations that relate the characteristics and
propagation of magnetic and electrical fields
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Blackbodies
• Theoretical concept– Perfect absorber and emitter
• Objects can exhibit blackbody-like characteristics at certain temperatures– Preferentially emits at specific
wavelength/frequency
• Can use as an approximation (usually pretty good)
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Temperature and Radiation• Temperature is defined as the average kinetic energy of
molecules in a substance• Anything that has a temperature radiates via the Stefan-
Boltzmann law:
J = εσT4 , where ε = emissivity and σ = 5.67x10-8 [W/m2K4]
• Wien’s Displacement law:
l = wavelength, b = 2.8977685(51)×10−3 m·K
• a (absorbtivity) + r (reflectivity) + t (transmissivity) = 1• Kirchoff’s Law: at thermal equilibrium, emissivity (ε) = a• Higher the temperature, greater the radiation emitted
T
bmax
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Brightness Temperature• Standard measurement for remote sensing
signal• More strictly correct is the spectral irradiance
I(l,T) obtained via Plank’s Law:
(J·s-1·m-2·sr-1·Hz-
1)
• But brightness temperature is easier: Tb = εTwhere Tb = brightness temperature (K), T = temperature of material (K), and ε = emissivity
1
2
3
12
,
kT
h
ec
hTI
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Simplify to Rayleigh-Jean law• Bypass Plank’s law: estimate Tb using the
spectral brightness Bl(T) from the Rayleigh-Jean law:
where k = Boltzmann constant, c = speed of light, Tb = brightness
temperature, and λ= wavelength.• Then back out the brightness temperature
4
2
bckT
TB
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Example of data collected
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Soil Thermal Properties• Thermal conductivity k: Heat transfer through a
unit area of soil (J/s m K, or W/m K)
• Heat capacity crb: Change in unit volume’s heat content per unit change in temperature (J/m3 K)
• Soil Thermal Inertia: • From remote sensing:
where DG = variation in surface heat flux, DT = Tmax – Tmin, and ω = 2p/86400s
T
GP
2
bsatsatcP
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Thermal Inertia and Soil Moisture
• As discussed, thermal properties depend upon many factors– Focus on soil moisture (because it’s awesome…
and where my research lies)
• Can create relationships between θ and thermal inertia (can’t separate the individual properties through remote sensing)
• We are now done with big scary equations and models
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Even more on this…• Can’t separate conductivity from capacity from just
remote sensing– Properties depend on too many variables– Can estimate thermal inertia P using model shown– Can estimate parameters in thermal inertia if know soil
type/texture/moisture content, etc.
• Due to variable needs in approximation, need more than one measurement– Can model heat flux through energy balance– Diurnal temperature changes are easy to get
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Figure Blitzkrieg!!!!
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Left: Nighttime temperature over bare soilRight: Daytime temperature over bare soil
Minacapilli and Blanda 2009
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(a) Ground heat flux G ≡ Q(0, t) (W m−2), and (b) surface (skin) temperature Ts ≡ T(0, t) (°C) measured at the Lucky Hill site in the Walnut Gulch Watershed, 5–16 June 2008.
Wang et al 2010
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Left: Soil thermal inertia P as a function of θRight: Normalized soil thermal inertia Kp as a function of
degree of saturation (normalized q)Lu et al. (2009)
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Idso et al 1976
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Idso et al1976
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Smits et al 2010
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References• Bachmann, J., R. Horton, T. Ren, and R R Van Der Ploeg. "Comparison of the Thermal Properties of
Four Wettable and Four Water-repellent Soils." Soil Sci. Soc. Am. J. 65 (2001): 1675-679. • Campbell, Gaylon S., and John M. Norman. Introduction to Environmental Biophysics. 2nd ed. New
York: Springer, 1998. • Hillel, Daniel. Introduction to Environmental Soil Physics. Amsterdam: Elsevier Academic, 2004. • Idso, Sherwood B., Ray D. Jackson, and Robert J. Reginato. "Compensating for Environmental
Variability in the Thermal Inertia Approach to Remote Sensing of Soil Moisture." Journal of Applied Meteorology 15 (1976): 811-17.
• Lu, Sen, Zhaoqiang Ju, Tusheng Ren, and Robert Horton. "A General Approach to Estimate Soil Water Content from Thermal Inertia." Agricultural and Forest Meteorology 149 (2009): 1693-698.
• Lu, Xinrui, Tusheng Ren, and Yuanshi Gong. "Experimental Inverstigation of Thermal Dispersion in Saturated Soils with One-Dimensional Water Flow." Soil Sci. Soc. Am. J. 73 (2009): 1912-920.
• Minacapilli, M., M. Iovino, and F. Blanda. "High Resolution Remote Estimation of Soil Surface Water Content by a Thermal Inertia Approach." Journal of Hydrology 379 (2009): 229-38.
• Smits, Kathleen M., Toshihiro Sakaki, Anuchit Limsuwat, and Tissa H. Illangasekare. "Thermal Conductivity of Sands under Varying Moisture and Porosity in Drainage-Wetting Cycles." Vadose Zone J. 9 (2010): 1-9.
• Wang, J., R. L. Bras, G. Sivandran, and R. G. Knox. "A Simple Method for the Estimation of Thermal Inertia." Geophysical Research Letters 37 (2010): L05404.
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Questions? Comments?