Downscaling of SMOS soil moisture using MODIS data... (N ... - SMAP

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Downscaling of SMOS soil moisture using MODIS data... (N ... - SMAP

Downscaling of SMOS soil moisture using

MODIS data over an agricultural site

Najib Djamai (Ph.D student)

Ramata Magagi (Professor)

Kalifa Goïta (Professor)

Mehdi Hosseini (Postdoctoral fellow)

3 rd Canadian SMAP Workshop

Ottawa, 20 – 21 March 2013


Introduction:

SMOS/ soil moistrure product

2D interferometric radiometer

L band (21 cm, 1.4 GHz)

Soil moistrure at 5 cm of depth

An accuracy of 4% on volumetric

soil moisture

Less than 3 days of revisit period

Spatial resolution ~ 40 km

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 2


Objectif

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 3

Estimate the soil moisture at 1 km

scale by a combination of SMOS

soil moisture product with MODIS

Aqua/Terra data


Study site

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 4


Data

June 13 th (JD 164) and 14 th (JD 165), 2010

MODIS Terra/Aqua

- Overpass times (local time):

10:30 (Terra) and 12:30 (Aqua)

SMOS SM product (SMUDP2 - v5.01)

- Overpass times (local time):

6:00 (Ascending) and 18:00 (Descending)

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 5


Methodology:

Downscaling relationship

SM 1km = < SM > + ∂SM

∂SMI . (SMI 1km −< SMI >)

(Merlin et al.,2013)

SM : Soil Moisture

SMI: Soil Moisture Index

< >: defined at SMOS scale (40 km)

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 6


Methodology:

Soil Moisture Index (SMI)

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 7

SMI = Soil Evaporative Efficiency (SEE)

(NDVI i ,Ts i )

Ts max

SMI =

Ts max − Ts i

Ts max − Ts min

Cold edge

Ts min


Methodology:

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 8

SM 1km = < SM > + ∂SM

∂SMI . (SMI 1km −< SMI >)

Linear model: SM = SMI. SM p

/ SM p : Soil parameter =


Downscaled SM


Results:

Soil moisture maps at 1 km resolution

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 9

SMOS / MODIS-Aqua

SMOS / MODIS-Terra


Results:

Downscaled SM vs in situ SM at 6 a.m.

Downscaled SM (m 3 /m 3 )

Downscaled SM (m 3 /m 3 )

Downscaled SM (m 3 /m 3 )

Downscaled SM (m 3 /m 3 )

SMOS / MODIS-Aqua

JD -164

0.5

0.4

0.3

0.2

Bias = 0 m 3 /m 3

0.1

RMSE = 0.06 m 3 /m 3

0

0 0.1 0.2 0.3 0.4 0.5

In situ SM (m 3 /m 3 )

JD-165

0.5

0.4

0.3

0.2

Bias = -0.02 m 3 /m 3

0.1

RMSE = 0.04 m 3 /m 3

0

0 0.1 0.2 0.3 0.4 0.5

In situ SM (m 3 /m 3 )

SMOS / MODIS-Terra

JD-164

0.5

0.4

0.3

0.2

Bias = 0.01 m 3 /m 3

0.1

RMSE = 0.06 m 3 /m 3

0

0 0.1 0.2 0.3 0.4 0.5

In situ SM (m 3 /m 3 )

JD-165

0.5

0.4

0.3

0.2

Bias = -0.02 m 3 /m 3

0.1

RMSE = 0.04 m 3 /m 3

0

0 0.1 0.2 0.3 0.4 0.5

In situ SM (m 3 /m 3 )

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 10


Results:

Downscaled SM vs TB (L band) at 6 a.m.

TB (K)

TB (K)

TB (K)

TB (K)

250

JD-164

SMOS / MODIS-Aqua

JD-165

TBv

Tbh

250

TBv

Tbh

200

200

R (TBv) = -0.62

R (TBh) = -0.58

150

0 0.2 0.4 0.6

SM (m 3 /m 3 )

250

JD-164

TBv

Tbh

R (TBv) = -0.52

R (TBh) = -0.48

150

0 0.2 0.4 0.6

SM (m 3 /m 3 )

SMOS / MODIS-Terra

JD-165

250

TBv

Tbh

200

200

R (TBv) = -0.53

R (TBh) = -0.5

150

0 0.2 0.4 0.6

SM (m 3 /m 3 )

R (TBv) = -0.56

R (TBh) = -0.52

150

0 0.2 0.4 0.6

SM (m 3 /m 3 )

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 11


Results:

In situ SM vs TB (L band) at 6.am

TB (K)

250

In situ SM vs TB

TBv

Tbh

230

210

190

170

R (TBv) = -0.5

150

R (TBh) = -0.44

0.2 0.3 0.4 0.5

In situ SM (m 3 /m 3 )

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 12


Future work

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 13

Using SMAPVEX data

What can we do for cloudy days

• This method is not useful for a cloudy day

because of MODIS data (Ts and NDVI)

availability

• For Canex-SM10 days , just 2 of 15 are no

cloudy days.


References

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 14

Merlin, O., Escorihuela, M.J., Miquel Aran Mayoral

M.A., Hagolle, O., Al Bitar, Kerr, Y., 2013. Selfcalibrated

evaporation-based disaggregation of

SMOS soil moisture: An evaluation study at 3 km

and 100 m resolution in Catalunya, Spain. Remote

Sensing of Environment 130, 25–38.

http://pages.usherbrooke.ca/canexsm10/


Acknowledgments

Downscaling of SMOS soil moisture using MODIS data over an agricultural site 15

The authors would like to thank:

• all of the participants in the Canadian Experiment for Soil

Moisture in 2010 (CanEx-SM10) and SMAP Validation

Experiment 2012 (SMAPVEX12)

• the CanEx-SM10 and SMAPVEX12 funding agencies.

• the European Space Agency (ESA) for providing the SMOS

data.


Thank you for your attention

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