Different Soil Moisture Dynamics are
Observed by SMOS and the
South Fork In Situ Soil Moisture Network
Brian Hornbuckle, Wesley Rondinelli, Jason Patton
Mike Cosh, Victoria Walker, Ben Carr, Sally Logsdon
SMOS vs In Situ Soil Moisture
what SMOS “sees” = 0-5 cm
SMOS vs In Situ Soil Moisture
what SMOS “sees” = 0-5 cm
in-situ network @ 5 cm
SMOS vs In Situ Soil Moisture
what SMOS “sees” = 0-3 cm
in-situ network @ 5 cm
SMOS vs In Situ Soil Moisture
hypothesis: soil layers observed by SMOS and
in situ networks are fundamentally different and
therefore will exhibit different soil moisture dynamics
what SMOS “sees” = 0-5 cm
in-situ network @ 5 cm
Experiment Design and Data
South Fork in situ network
20 sites within 40 x 40 km area
soil moisture sensors at 5 cm
calibrated to soil at each site
80% maize (corn) and soybean
SMOS pixel centers
soil moisture, m3 m-3
shading: 9 periods of examination after rainfall
South Fork network soil moisture,
SMOS A, SMOS B, SMOS C
day of year, 2013
mean precipitation over network, mm
Experiment Design and Data
Experiment Design and Data
third period, June/July
South Fork network soil moisture
SMOS soil moisture
days after rain
days after rain
exponential fits:
Experiment Design and Data
exponential fits
third period, June/July
South Fork network soil moisture
SMOS soil moisture
days after rain
days after rain
Results: rate of soil drying
m3 m-3 per day
Case
SF
A
B
C
1
2
0.02 0.04 0.04 0.08
0.03 0.17 0.19 0.15
3
0.03 0.12 0.10 0.10
4
5
6
7
8
9
0.02
0.01
0.02
0.01
0.00
0.01
0.12
0.02
0.04
0.02
0.10
0.06
0.07
0.02
0.04
0.01
0.06
0.04
0.08
0.01
0.04
0.02
0.07
0.05
Results: rate of soil drying
m3 m-3 per day
Case
SMOS initial rate of drying
always greater than or equal to
South Fork network.
SF
A
B
C
1
2
0.02 0.04 0.04 0.08
0.03 0.17 0.19 0.15
3
0.03 0.12 0.10 0.10
4
5
6
7
8
9
0.02
0.01
0.02
0.01
0.00
0.01
0.12
0.02
0.04
0.02
0.10
0.06
0.07
0.02
0.04
0.01
0.06
0.04
0.08
0.01
0.04
0.02
0.07
0.05
Results: rate of soil drying
m3 m-3 per day
Case
SMOS initial rate of drying
always greater than or equal to
South Fork network.
SMOS and network
soil moisture dynamics
are different.
SF
A
B
C
1
2
0.02 0.04 0.04 0.08
0.03 0.17 0.19 0.15
3
0.03 0.12 0.10 0.10
4
5
6
7
8
9
0.02
0.01
0.02
0.01
0.00
0.01
0.12
0.02
0.04
0.02
0.10
0.06
0.07
0.02
0.04
0.01
0.06
0.04
0.08
0.01
0.04
0.02
0.07
0.05
Different dynamics = different layers?
SMOS and network
soil moisture dynamics
are different.
Does this imply that
SMOS and the network
observe different
layers of soil?
point-scale model of energy and water transport
Different dynamics = different layers?
point-scale model of
energy and water transport
SMOS and network
soil moisture dynamics
are different.
Does this imply that
SMOS and the network
observe different
layers of soil?
Different dynamics = different layers?
TDR at 1.5 cm and 4.5 cm,
16 sites within 1 km2
SMOS and network
soil moisture
1 km dynamics
are different.
Does this imply that
SMOS and the network
observe different
layers of soil?
TDR at 1.5 cm = 0-3 cm soil layer
TDR at 4.5 cm = 3-6 cm soil layer
soil moisture and temperature
Different dynamics = different layers?
SMOS and network
soil moisture dynamics
are different.
Does this imply that
SMOS and the network
observe different
layers of soil?
TDR at 1.5 cm and 4.5 cm,
16 sites within 1 km2
Different dynamics = different layers?
SMOS and network
soil moisture dynamics
are different.
Does this imply that
SMOS and the network
observe different
layers of soil?
Yes, SMOS and the
South Fork in situ network
observe different layers of soil.
Implication for satellite validation?
SMOS soil moisture, m3 m-3
0.5
SMOS and network
observe different
layers of soil.
0.4
0.3
Does this explain why
SMOS is “dry”
compared to the
South Fork network?
0.2
0.1
0.1
0.2
0.3
0.4
0.5
South Fork network soil moisture, m3 m-3
Al Bitar et al., 2012
Gherboudj et al., 2012
Collow et al., 2012
Magagi et al., 2013
Implication for satellite validation?
SMOS overpass times
2011 growing season
point-scale model of
energy and water transport
2011 growing season
Implication for satellite validation?
SMOS overpass times
2011 growing season
point-scale model of
energy and water transport
No significant bias
between 0-3 cm and
4-6 cm soil layers
in 1-D model.
RMSE = 0.04 m3 m-3
Implication for satellite validation?
TDR at 1.5 cm and 4.5 cm,
16 sites within 1 km2
2011 growing season
Implication for satellite validation?
SMOS overpass times
2011 growing season
TDR at 1.5 cm and 4.5 cm,
16 sites within 1 km2
No significant bias
between TDR at 1.5 cm
and TDR at 4.5 cm.
RMSE = 0.02 m3 m-3
Conclusions
SMOS and the South Fork in situ network
exhibit different soil moisture dynamics and
therefore observe different layers of soil.
This does not appear to cause a bias
between SMOS and in situ networks.
However, it may be responsible
for a significant amount of the RMSE
in the relationship between
SMOS and in situ network soil moisture.
More information: Rondinelli, Hornbuckle et al., 2015, J. Hydrometeor.
Conclusions
Why is SMOS dry?
A) Ground temperature used to interpret SMOS is too low? No.
B) Corrupted by RFI e.g. from airport radars? Not likely.
C) Not using correct soil type? Likely.
D) Not using correct vegetation? Maybe.