1. YHKGEWEX May June 2007 Land Surface Flux Workshop Soil moisture retrieval from space a review? Claire Gruhier, Silvia Juglea, Patricia deRosnay and Yann Kerr

2. YHKGEWEX May June 2007 Land Surface Flux Workshop Atmosphere Control (Radiation) Surface Control (Soil Moisture) Surface Control (Freeze/Thaw) Main factors controlling the water, energy and carbon fluxes Churkina & Running, 1998

3. YHKGEWEX May June 2007 Land Surface Flux Workshop What is Soil moisture? Water in –the first mm –The first centimeters –In the litter layer –The root zone (Vadose) –The water table –The total –The total including interception Antecedent precipitaion index An adjusting variable allowing models to run and to give ET A soil wetness index A red coulour in GRACE gravity fields Does it exist? etc

4. YHKGEWEX May June 2007 Land Surface Flux Workshop Measuring soil moisture Laboratory –Oven-drying soil samples –samples analysis –chemical methods In situ –neutron probes –resistivity –Capacity probes Remote sensing –SW –SWIR –IR –passive and active microwaves  Remote sensing using microwaves opens a way towards surface soil moisture mapping

5. YHKGEWEX May June 2007 Land Surface Flux Workshop ESTIMATION DE L’HUMIDITE DU SOL PAR TELEDETECTION RADAR Soil Moisture Remote Sensing ??? P. de Rosnay, F. Baup, E. Mougin, C. Gruhier, F. Timouk, P. Hiernaux, I. Chenerie,Y. Kerr

6. YHKGEWEX May June 2007 Land Surface Flux Workshop Probing depth? Local calibration:

7. YHKGEWEX May June 2007 Land Surface Flux Workshop Field measurements: Soil moisture dynamics Ebangui Mallam soil moisture vertical profile before after rain: P= 61mm DW=51mm 2.5m surf 0 12 SM %m3/m3 Agoufou SM dynamics at different depths

8. YHKGEWEX May June 2007 Land Surface Flux Workshop Field measurements for upscaling purpose: Transect measurements -> kilometric to 50km scale information Surface Soil Moisture (SSM) - 1km transects: every 10 m. - 50km: every 1km Total ~60 transect measurements for 2004-2006 Relationship between: local (station) & kilometric (transects) surface soil moisture -> kilometric calibration of SSM

9. YHKGEWEX May June 2007 Land Surface Flux Workshop Influence of Ws & roughness Active microwaves (radar) s =1, 0.8, 0.6, 0.4 cm Ws=30, 25, 20, 15 % P. Waldteufel 1999

10. YHKGEWEX May June 2007 Land Surface Flux Workshop 1 - En Actif: ENVISAT/ASAR MALI (Agoufou): Baup et al 2007a et 2007b Niger (Kori de Diantandou): (Zribi et al 2006) Précision d’inversion: 2.8% et 2.2% sur les 2 sites Résol: ~ 1km, 15j

11. YHKGEWEX May June 2007 Land Surface Flux Workshop - Methodological development and validation over Agoufou intensive site - Use of WS mode, HH polarization - Normalization function accounts for vegetation angular effect: - Dry season (Nov-May) - Wet season (Jun-Oct) Active Microwave Remote Sensing: ENVISAT/ASAR Baup et al. RSE 2006 (submitted)

12. YHKGEWEX May June 2007 Land Surface Flux Workshop Inter-annual variations of backscatter (ERS-WSC) in the Sahelian area Jarlan et al.

13. YHKGEWEX May June 2007 Land Surface Flux Workshop ERS-WSC / NDVI VGT Comparison in Sahel Jarlan et al.

14. YHKGEWEX May June 2007 Land Surface Flux Workshop Galactic TEC O2, IWC, T, ILWC, rain, and resp heights Tv, , WC, structure,S ,Ts,S/C, , SM

15. YHKGEWEX May June 2007 Land Surface Flux Workshop T B sensitivity Kerr, 1997

16. YHKGEWEX May June 2007 Land Surface Flux Workshop Influence of W V on radiometric sensitivity to Ws In order to penetrate vegetation cover, lowest possible frequencies should be selected. F < 1GHz : large Faraday effects Then the protected frequency is : 1.41 GHz ! Kerr and Jackson, 1995

17. YHKGEWEX May June 2007 Land Surface Flux Workshop Jackson 2001

18. YHKGEWEX May June 2007 Land Surface Flux Workshop Wigneron et al., 95 Retrievals

19. YHKGEWEX May June 2007 Land Surface Flux Workshop Passive Microwave Remote Sensing Inversion of AMSR Brightness temperature Statistical inversion based on multiple configuration observation of the surface, provided by AMSR polarization H and V. SM* = a0 + a1 PR +a2 (TBv-TBh) ; SM* retrieved Surface Soil Moisture PR = (Tbv-TBh)/(TBv+TBh) ; Polarization ratio from AMSR BT measurements Cost function based on minimization of RMSE Validation of correlation, RMSE, Efficiency, Mean Bias On going: investigate further statistical inversion (multi freq C & X bands) and addresse semi-empirical regression based on C-band modeling Range -1 to 1 (Best agreement)

20. YHKGEWEX May June 2007 Land Surface Flux Workshop Passive Microwave Remote Sensing: AMSR AMSR on Gourma Supersite : NASA products overestimate SSM Specific SSM inversion is developed based in statistical regression of bi- polarized measurements. Validation preliminary results: RMSE(%m3/m3) Correlation Efficiency MeanBias (%m3/m3) 2006 2005 AMSR-NASA 4.32 0.54 -0.8 3.3 5.04 0.45 -0.37 3.25 AMSR-retrieved 2.77 0.5 0.25 0.01 3.8 0.46 0.21 -0.03 -> Statistical retrieval slightly improves the accuray of AMSR SSM compared to NASA products – Further investigations required to take advantage of multispectral (C & X bands)

21. YHKGEWEX May June 2007 Land Surface Flux Workshop SMOSREX and Sud-Ouest France, Toulouse Comparison between AMSR-E and surface soil moisture over 3 networks for 2005

22. YHKGEWEX May June 2007 Land Surface Flux Workshop GoREx (NAFE) Autralia, Goulburn River catchment Comparison between AMSR-E and surface soil moisture over 3 networks for 2005

23. YHKGEWEX May June 2007 Land Surface Flux Workshop AMMA – Gourma region Mali, Agoufou Comparison between AMSR-E and surface soil moisture over 3 networks for 2005

24. YHKGEWEX May June 2007 Land Surface Flux Workshop Passive Microwave Remote Sensing: AMSR Aug 2 nd decade Aug 1 st decade July 3 nd decade AMSR-E Land 3 NASA products (Njoku et al 2003): Soil Moisture : -> 1) Evaluation with ground soil moisture network and upscaling measurements Radiometric measurements (Brightness temperatures): -> 2) Development of statistical inversion over the Gourma super site

25. YHKGEWEX May June 2007 Land Surface Flux Workshop EVOLUTION OF MEAN SOIL MOISTURE FOR JANUARY (SMMR + AMSR) SMMRAMSR YEAR FOR JULY SM X10

26. YHKGEWEX May June 2007 Land Surface Flux Workshop EVOLUTION OF SOIL MOISTURE FOR JULY SMMR (regression AMSR)

27. YHKGEWEX May June 2007 Land Surface Flux Workshop Issues Topography Mixed pixels Sub pixel heterogeneity Saturations (water, forests, snow?) Root Zone Soil moisture, Freezing litter A word about forests...

28. YHKGEWEX May June 2007 Land Surface Flux Workshop COUPLING INTERACTIVE VEGETATION MODEL (ISBA-AGS) and RT MODELS Wigneron et al., 2001

29. YHKGEWEX May June 2007 Land Surface Flux Workshop Wigneron et al 2000

30. YHKGEWEX May June 2007 Land Surface Flux Workshop Coupling and disaggregation Scheme Wg mean, W mean t SVATSIMPLE LE, Rn,H,G percolation Infiltration Subsurface flow Saturation excess Runoff TOPMODEL Wg mean, W mean t + dt { Wg i }, { W i } t + dt Soil proprieties + DTM Pellenq et al., 2001

31. YHKGEWEX May June 2007 Land Surface Flux Workshop Spatialised Disaggregation Results OBSERVED SIMULATED TOPOGRAPHY SIMULATED TOPOGRAPHY + SOIL DEPTH DOY 610 R 2 =0.895 R 2 =0.88 Correlation: Pellenq et al., 2001

32. YHKGEWEX May June 2007 Land Surface Flux Workshop Simulated TB 1km 55km footprint 55km NIGER: Meso scale TB simulations: ISBA + C-MEB (1km²) C-band Microwave Emission of the Biosphere (Pellarin et al., 2007, in prep) Agrégation/désagrégation Simulated TB 25km-reggrided AMSR-E TB Level 3 25km product Résol ~ 25km/1j -> désagrégation à 1km/1j

33. YHKGEWEX May June 2007 Land Surface Flux Workshop Use of Altimetry Principle –Measure water heights wit use of alytimeters, –Gives amount of water Issues –Requires width and shape of bottom –Validity of water masks –Small bodies wrt resolution

34. YHKGEWEX May June 2007 Land Surface Flux Workshop Water fractions and ESRI

35. YHKGEWEX May June 2007 Land Surface Flux Workshop Use of gravimetry Principle –Measures changes of gravimetric field –Gives changes in water stocks Issues –A signal is there but –Never validated –Strange results not yet explained

36. YHKGEWEX May June 2007 Land Surface Flux Workshop Seasonal changes in gravity as seen by GRACE (truncated at n = 10) and predicted from a mean hydrology model (from Andersen et al. 2005a), unit of the amplitude is μGal (= 10-8 m s-2) unit of the phase is days wrt January first.

37. YHKGEWEX May June 2007 Land Surface Flux Workshop Standard deviation (in μGal) of the annual changes from 5 different hydrology models (from Andersen et al. 2005a).

38. YHKGEWEX May June 2007 Land Surface Flux Workshop Hydrological load (in mm of water equivalent) from the GLDAS model (left) and induced gravity changes (in μGal) (center) and ground vertical displacement (in mm) (right) for March and September 2003.

39. YHKGEWEX May June 2007 Land Surface Flux Workshop Differences for March and September 2003 of the gravity field (in m.s-2) between hydrological models and GRACE observations; upper left: raw LadWorld model corresponding at a truncation of degree n = 180 (1° x 1°); upper right same but truncated at n = 15 and lower center GRACE observations truncated at n = 15.

40. YHKGEWEX May June 2007 Land Surface Flux Workshop Other issues Validation Sea variations –Validation experiments Antarctica …..

41. YHKGEWEX May June 2007 Land Surface Flux Workshop Conclusions? Gravimetry –Needs validation Active SAR –Relative values at best. –See scat Active Scat –Very complementary –Freeze thaw Altimetry –Complementary Passive low freq –Needs aux data –Still some issues Why should P=ET+R+  S?

42. YHKGEWEX May June 2007 Land Surface Flux Workshop Thank you …..Any questions ? http//www.cesbio.ups-tlse.fr/us/indexsmos.html