Main outcomes of the CoSMOS/NAFE campaign for the validation of the SMOS soil moisture retrieval algorithm

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HAL Id: hal-02819386

https://hal.inrae.fr/hal-02819386

Submitted on 6 Jun 2020

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Main outcomes of the CoSMOS/NAFE campaign for the validation of the SMOS soil moisture retrieval algorithm

Kauzar Saleh Contell, Yann H. Kerr, Gilles Boulet, Maria-José Escorihuela, Philippe Maisongrande, Philippe Richaume, Patricia de Rosnay, Jean-Pierre

Wigneron, Ernesto Lopez-Baeza, Jennifer Grant, et al.

To cite this version:

Kauzar Saleh Contell, Yann H. Kerr, Gilles Boulet, Maria-José Escorihuela, Philippe Maisongrande, et al.. Main outcomes of the CoSMOS/NAFE campaign for the validation of the SMOS soil moisture retrieval algorithm. 10. Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment, Labo/service de l’auteur, Ville service, Pays service., Mar 2008, Firenze, Italy. �hal- 02819386�

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The CoSMOS/NAFE campaign for the

validation of the SMOS retrieval algorithm over land

K. Saleh, Y. Kerr, P. Richaume, J.P. Wigneron,

S. Delwart, M.J. Escorihuela, P. Maisongrande, G. Boulet and the CoSMOS/NAFE team

Microrad’08- Firenze 11-14 March 2008

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2 1/ ESA CoSMOS study (2007-2008): Overview

EVALUATION OF THE

SMOS SM LEVEL 2 (L2) ALGORITHM USING

AERIAL DATA

VALIDATION OF MICROWAVE

MODEL L-MEB

‘SPECIAL ISSUES’

(e.g. sun-glint over land, interception …)

ANCILLARY DATA?

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1/ ESA CoSMOS study (2007-2008): Overview

Training for upcoming

SMOS Validation campaigns EVALUATION

OF THE

SMOS SM LEVEL 2 (L2) ALGORITHM USING

AERIAL DATA

‘SPECIAL ISSUES’

(e.g. sun-glint over land, interception …)

VALIDATION OF MICROWAVE

MODEL L-MEB

SENSITIVITY TO

ANCILLARY DATA?

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1/ CoSMOS-NAFE Experiment: Overview & objectives

6-week campaign

2 L-band sensors onboard two aircrafts (2 week overlap) Focus area: ~60 km x 60 km farming area

Collaboration between NAFE experiment (University of Melbourne), researchers from Europe, US and Australia, ESA

Goulburn River catchment

4

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Focus farms area ~ 60 km x 60 km

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CROP AREAS VWC: 0.3-2.7 kgm-2

Merriwa Park Illogan

Pembroke Illogan

6

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GRAZING AREAS VWC: 0.1-1 kgm-2

Dales Dales

Stanley

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2/ Instruments

a) ESA flights- EMIRAD

EMIRAD POLARIMETRIC RADIOMETER (TUD) onboard Aero Commander 500S

8 Nadir ~ 40 deg Full-Stokes

IR Radiometer onboard

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-30 -20 -10 0 10 20 30

-180 -120 -60 0 60 120 180

Across Flight Track Off-Nadir Angle ( deg )

Amplitude ( dBi )

3L 2L 1L 1R 2R 3R

<< Left Right >>

b) NAFE flights- PLMR

PLMR RADIOMETER (UM) onboard Diamond Eco-Dimona motor glider

2/ Instruments

+/-7,+/-21.5,+/-38.5

H & V pol

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3/ L-band data processing

Tbi,j

1 Antenna projected onto the surface

f(aircraft attitude, antenna orientation, no slopes)

c c c g g g g g g g g g g g g

c f f

2 Land-use from Landsat classif.

(e.g. crop,grass,forest) +

Ancillary surface data

5 Weighting by antenna gain &

integration

4 Transportation of simulated Stokes vector to antenna

level

3 Tbi,j

Simulated Tbi,j using SMOS BBs

6 Comparison to measured Stokes

and retrievals

10

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3/ L-band data processing

Simulations of TB and retrievals take into account

antenna pattern and

observed surface

Large aperture : 3dB area up to ~1 km (off-nadir)

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13/11 14/11 15/11 17/11

20/11 21/11 22/11 23/11

27/11 29/11 03/12 09/12

EMIRAD

rainfall

EMIRAD EMIRAD

EMIRAD

EMIRAD EMIRAD EMIRAD

EMIRAD EMIRAD

EMIRAD

4/ L-BAND measurements

[K]

12

PLMR along-track 02/11,09/11,16/11,23/11

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4/ L-BAND measurements

EMIRAD

-Dry to wet soil ΔTB~40 K at nadir (for ΔSM~ 0.3 m3m-3) -Low angular variation in TB between Nadir and 40 deg ΔTBv < 5-10 K for dry soil, ΔTBv < 15-20 K for wet soil

-Rather stable TB measurements across the farm for dry soil nadir

40 deg

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5/ Modelling

What do L-MEB simulations indicate?

SM=0.38 (σ=0.07) m3m-3 SM=0.22 (σ=0.05) m3m-3

High-res area

14 PLMR Along track

Wheat,

Clay-loam

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5/ Modelling

What do L-MEB simulations indicate?

SM=0.38 (σ=0.07) m3m-3 SM=0.22 (σ=0.05) m3m-3

High-res area

Wheat, Clay-loam

PLMR

Along

track

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5/ Modelling

What do L-MEB simulations indicate?

EMIRAD and PLMR over the same wheat area on the same day - Dry soil

(green, TB from Hr and τ

_n

from PLMR) (black, same but for τ

_n

**= 0.06*LAI)**

15 EMIRAD Along

track PLMR

Along track

Tsfce=294 K Tsfce=304 K

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5/ Modelling

What do L-MEB simulations indicate?

Γ= Γ *exp(-Hr/cos

^Np

(θ)) HR~0.6, ploughed soil, Clay-loam, black basalts

•Literature: crops Hr=[0.1-0.7]

•Sensitivity of HR to dielectric model

•No clear sensitivity of HR to SM

PLMR Along track

Explore next if default b’(LAI) too low for wheat?

b’=τ

_n

/LAI

•Field VWC & b=0.08 -->

τ

_nwheat [ 0.05-0.1]

Tau from LAI Tau from VWC Tau free

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6/SM Retrievals

CROPS Clay, HR=1 ΔSM_station ~ 0.3 m3m-3

Rain -5 d Rain -7 d Rain -10 d

Rain -0 d Rain -0 d Rain -4 d

EMIRAD Along

track

17

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6/ SM Retrievals

CROPS Clay, sparse grass- HR=1 ΔSM_station ~ 0.3 m3m-3

Rain -5 d Rain -7 d Rain -10 d

Rain -0 d Rain -0 d Rain -4 d

Rain -5 d Rain -7 d Rain -10 d

Rain -0 d Rain -0 d Rain -4 d

EMIRAD Along

track

Silt-loam,crops , HR=1 ΔSM_station ~ 0.3 m3m- ¹⁸

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19 7/ Conclusions

i) L-band processing ‘close’ to the SMOS L2 approach

(aggregated TBs within the antenna pattern, SMOS BBs)

• Basis for upcoming airborne campaigns over land

ii) The CoSMOS study is now in the algorithm validation phase

• Focus on small areas with dense sampling to characterise vegetation and soil emission, next step is moving to the farm scale

iii) Both PLMR and EMIRAD data produce a TB signature that requires large Hr

• Hr is usually fitted in experiments, how do we fit it globally?

• Hr = f(land use, soil type, std)

iii) Once roughness is fitted, changes in the retrieved and

measured SM are comparable

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SM, T,Hr,Tau

Measured Retrieved

MW validation

SM

validation

7/ Conclusions

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4/ Modelling

What do L-MEB simulations indicate?

Mean HR=0.6, ploughed soil, 70% clay, black basalts

Literature: crops Hr=[0.1-0.7]

Field WC & b=0.08 --> Hr~1, higher TB error

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3/ L-band data processing

Zone 2. Farm scale

Cell-to-cell comparisons between surface data and L-band retrievals

e.g. comparisons to SM when available e.g. LAI and retrieved optical depth

Gridding pixel 3dB area

Scattered SM data

1x

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Figure 6b. Temperatures at Merriwa Park: Yellow: IR station (when available), Black: surface 2.5 cm, Dotted line: Flights PLMR