understanding soil moisture transport.pptx
TRANSCRIPT
Pang-Wei Liu1, Roger De Roo2, Anthony England2,3,
Jasmeet Judge1
1. Center for Remote Sensing, Agri. and Bio. Engineering, U. of Florida
2. Atmosphere, Oceanic, and Space Sciences, U. of Michigan
3. Electrical Engineering and Computer Science, U. of Michigan
UFUNIVERSITY of
FLORIDA1
Outline
Introduction & Motivation
MicroWEX-5
MB Model
Methodology
Results
Conclusions
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Introduction & Motivation Soil moisture (SM) is an important factor
In hydrology: evapotranspiration, infiltration, surface runoff, and
groundwater recharge.
In agriculture: crop growth and yield.
Satellite missions for SM:
AMSR-E, NASA and JAXA, 2002
– V- & H-pol passive at C-band.
– Spatial resolution at 6.25-57km and repeat coverage in 1-2 days.
SMOS, ESA, Nov. 2009.
– V- & H-pol passive at ~1.4GHz (L-band).
– Spatial resolution at 40-50km and repeat coverage in 2-3 days
SMAP, NASA, Oct. 2014.
– Active at 1.26 GHz and passive at 1.41GHz.
– Spatial resolution of active at 1-3 km and of passive at ~40km and
repeat coverage in 2-3 days.
Provide TB for assimilation and soil moisture retrieval.
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Introduction & Motivation
Problem: The near-surface SM is highly dynamic, particularly in sandy soils.
Current forward microwave algorithms typically use SM averaged
over 0-5cm may result in unrealistic TB.
Objectives:
To determine the vertical resolution of the soil moisture necessary
to provide realistic TB at L-band for bare soils.
To utilize combined C- & L- band observations to determine the
surface roughness and moisture, and the vertical resolution in the
soil.
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Microwave Water and Energy Balance
Experiments (MicroWEXs)
Series of season-long experiments
conducted at a 9-acre field in NC Florida.
Fifth MicroWEX (MicroWEX-5): growing
season of sweet corn from March 9 (DoY
68) through May 26 (DoY 146) in 2006
The bare soil period: from DoY 68 to 95;
LAI < 0.3
Soil moisture and temperature values
were observed every 15 minutes at the
depths of 2, 4, 8, 16, 32, 64, and 120cm.
V- & H-pol. TB at C-band and H-pol. TB at
L-band every 15 minutes.
Soil Texture Parameters
Porosity (m3/m3) 0.37
Sand (% by vol.) 89.4
Clay (% by vol.) 7.1
Silt (% by vol.) 3.5
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Mesh board for soil roughnessLiDAR for soil roughness
Mesh Board
Correlation Length (cm) rms Height (cm)
1 15.5 0.8
2 8.1 0.7
3 5.3 0.4
LiDAR
Correlation Length (cm) rms Height (cm)
1 11.3 0.7
2 9.1 0.7
3 3.0 0.4 6
MB Model
Typical Approaches Radiative Transfer Equation: zero order approximation
TBsoil, p = Teff ∙ ep
– Teff Soil temperatures at surface (TIR) and deep layer (~50cm).
– ep= (1 - rp) rp (εr, roughness)
– εr (SM, soil texture) dielectric models: Dobson et al., 1996 and
Mironov et al., 2009
Rough surface models
– Semi-empirical model: Q-h model Wang & Choudhury, 1981 rp (εr,
rmsh, f, θ).
– Empirical model Wegmüller & Mätzler, 1999 rp (εr, rmsh, f, θ); 1-
100GHz.
– Physically-based model: IEM (Fung et al., 1992) ep (εr, rmsh, cl, f, θ);
applicable for wide range of surfaces.
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Comparison with observations
VSM0-5 from MicroWEX-5
Soil porosity = 0.37
Rms height = 0.616 cm
Correlation length = 8.4 cm
Looking angle = 50o
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Methodology
Modifications in the MB model: Soil:
– Discrete layers with non-uniform temperature and SM.
– Rough surface
– Semi-infinite lower boundary
Sandy soils are more porous at the surface.
– Top 1.5 cm divided into 7 layers.
– 1.5 – 32.5 cm divided into 1cm thick layers.
– > 32.5 cm layer thickness increases with depth
1st order RTE
– Single reflection considered at each layer interface.
– IEM model is applied at layer 1 - rough surface
– TB contributions from each layer combine to obtain the total TB
TB
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Methodology
Refractive mixing model for ε
– Modified Mironov’s model (2010)
Use C-band (6.7 GHz) TB observations to estimate
– Surface roughness rms height and correlation length
– Soil porosity in top 1mm
– SM in top 1mm
These parameters are used with the SM observation from lower
layers to estimate H-pol. TB at L-band.
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Results
Estimation of rms height, correlation length, and porosity
in top 1mm
Provide the best estimate
during the dry (SM1mm =
0.01) and the wet (SM1mm =
0.29) periods
The SM from 0-2.5cm
linearly interpolated-Rms height = 0.41cm
-Correlation length = 8.4cm
-Soil porosity = 0.55
SM at > 2.5cm from
MicroWEX-5
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Results
Estimation of SM in top 1mm.
SM in the top 1mm b/w
breaking points linearly
interpolated
Rms height = 0.41cm
Correlation length = 8.4cm
Soil porosity = 0.55
0.29 0.25 0.16 0.18 0.18 0.02 0.01 0.10 0.10 0.01
MicroWEX-5
Best estimation
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Results
Comparison of SM in the top 1mm with 0-5 cm SM during MicroWEX-5
Soil porosity: 1mm = 0.55; rest layers =0.37
SM profiles at wet, medium, and dry points
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MicroWEX-5
Results
Comparison of:
TB from MicroWEX-5
Case1: TB using SM 0-5 cm from MicroWEX-5.
Case2: TB using best estimate of SM, porosity, and roughness in the top
1mm from C-band; SM from 1mm-2.5cm linearly interpolated; SM >
2.5cm from MicroWEX-5.
Case3: TB using average of the best estimate in the top 1mm from C-
band and SM at 2.5cm from MicroWEX-5; SM > 2.5 cm from MicroWEX-
5; SM in top 1mm at the time of event from C-band for up to 30minutes.
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Results
Extension of methodology to the another drydownperiod from DoY 87.5-90.5
Estimation of SM in top 1mm.
0.32 0.28 0.19 0.19 0.01 0.10 0.01
MicroWEX-5
Best estimation
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SM in the top 1mm b/w
breaking points linearly
interpolated
Rms height = 0.41cm
Correlation length = 8.4cm
Soil porosity = 0.55
Comparison of SM in the top 1mm with 0-5 cm SM during MicroWEX-5
Soil porosity: 1mm = 0.55; rest layers =0.37
SM profiles at wet, medium, and dry points
Results
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MicroWEX-5
Results
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Comparison of:
TB from MicroWEX-5
Case1: TB using SM 0-5 cm from MicroWEX-5.
Case2: TB using best estimate of SM, porosity, and roughness in the top
1mm from C-band; SM from 1mm-2.5cm linearly interpolated; SM >
2.5cm from MicroWEX-5.
Case3: TB using average of the best estimate in the top 1mm from C-
band and SM at 2.5cm from MicroWEX-5; SM > 2.5 cm from MicroWEX-
5; SM in top 1mm at the time of event from C-band for up to 30minutes.
Conclusions
SM 0-5cm is not adequate for estimating realistic TB
at L-band in sandy soils, particularly during and
immediately following precipitation/irrigation events.
TB at C-band may be used to derive soil surface
characteristics such as roughness, porosity, and SM.
TB at L-band may be obtained using the derived
properties and the observations at 2cm.
Future work: Extending/generalizing the
methodology for larger applicability.
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Acknowledgment
NASA Terrestrial Hydrology Program (NASA-THP-
NNX09AK29G)
MicroWEX-5 was supported by the NSF Earth
Science Division (EAR-0337277) and the NASA New
Investigator Program (NASA-NIP-00050655).
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Thank You For Attention
Questions??
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While the soil saturated
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The VSM at 1mm layer was
set at 1% in dry period.
- rmsh=0.616cm, cl=8.4cm
- soil porosity = 0.5
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The VSM at 1mm layer was set
at 29% in the wet period.
-rmsh=0.41cm, cl=8.4cm
-Porosity = 0.5
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Results Comparison of radiative emission models.
1. Overall, 484 pairs of soil
moisture and temperature
profiles were applied.
2. The average difference is
within 3K at L-band.
3. 1st order model was applied
for further work.
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