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Soil Physics 2010
Outline
• Announcements• More on thermal properties• More on evaporation
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Soil Physics 2010
Announcements• Review session today, 11:00-1:00,
room 1581 Agronomy
• More sessions will be scheduled for next week
• 1 more homework will be assigned
• Quiz? No, not today.
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Soil Physics 2010
Measuring Thermal Properties in the Field
Inverse methods using many measurements at multiple depths and times?
ThermalDiffusivity
DT
VolumetricHeat Capacity
c
ThermalConductivity
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Soil Physics 2010
Assumptions:DT constantNo water movementNo latent heat movementSine wave
…not necessarily!
Measuring Thermal Diffusivity in the Field
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Soil Physics 2010
Measuring Thermal Diffusivity in the Field
The amplitude method:
2
2
1
221
ln2
AA
zzDT
The phase change method: 2
21
221
2
zzDT
Every sensor is a temperature sensor. But if you’re clever, you can use it to measure something else as well.
-- Gaylon Campbell
?
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Soil Physics 2010
Suppose we measure T and :We get DT from amplitude or phase shiftWe get directlyFrom DT and we calculate cFrom DT and c we calculate …?
Estimating other properties in the field
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Soil Physics 2010
Evaporation
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Soil Physics 2010
Evaporation Lawrence et al., 2007
Evaporation from the soil can be an important part of the total water budget!
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Soil Physics 2010
Evaporation
Evaporation may be limited by:• Energy• Water supply• Vapor transport
time
e, m
m/d
ay Stage I
Stage II
Stage III
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Soil Physics 2010
Evaporation
Evaporation may be limited by:• Energy in• Water in• Vapor out
time
e, m
m/d
ay Stage I
Stage II
Stage III
Water available;(mostly) energy-limited
Energy available;Transport limiting:
water upvapor out
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Soil Physics 2010
Main limitations on actual evaporation from soil• Stage I: evaporation from the surface
• Energy available at surface• Vapor pressure deficit in air near the surface• Transport of vapor away from the surface
• Stage II: evaporation from a retreating drying front• Flow of liquid water to the drying front
• Stage III: evaporation from a stationary drying front• Diffusion of water vapor from the drying front to air above
the soil surface
time
e, m
m/d
ay Stage I
Stage II
Stage III
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Soil Physics 2010
Evaporation insights and innovations 1:Maria Dragila: Enhanced evaporation from fractures
Daytime:Hot dry soil surfaceCooler, moister fracture faceEvaporation limited by diffusion
Nighttime:Cool dry soil surfaceWarmer, moister fracture faceConvection in the fracture
enhances evaporation