FR3.L10.4: SMOS SOIL MOISTURE VALUES EVALUATION OVER SAHELIAN AREA

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FR3.L10.4: SMOS SOIL MOISTURE VALUES EVALUATION OVER SAHELIAN AREA

  1. 1. SMOS L-Band Brightness Temperatures Compared to Other Passive Microwaves Sensors over West Africa Area C. GRUHIER (1), Y. KERR (1), F. CABOT (1), A. MIALON (1), T. PELLARIN (2), P. DE ROSNAY (3), M. GRIPPA (4) [email_address] (1) CESBIO Toulouse France (2) LTHE Grenoble France (3) ECMWF Reading UK (4) LMTG Toulouse France <ul><li>Introduction </li></ul><ul><li>Study area </li></ul><ul><li>Soil Moisture and Ocean Salinity </li></ul><ul><li>Comparison of Brightness Temperatures </li></ul><ul><li>Soil moisture product validation </li></ul><ul><li>Conclusion </li></ul>IGARSS Session SMOS 26 – 30 July 2010 Honolulu, Hawaii
  2. 2. Introduction Scientific context <ul><li>Why study soil moisture ? </li></ul><ul><li>One of the most important variable which strongly influences the soil-vegetation-atmosphere fluxes. </li></ul><ul><li>How access to this information ? </li></ul><ul><li>Ground measurements </li></ul><ul><li>Remote sensing </li></ul><ul><li>Modelling </li></ul><ul><li>Soil Moisture and Ocean Salinity </li></ul><ul><li>Passive microwaves sensor in L-band </li></ul><ul><li>Launched the 2th November 2009 </li></ul><ul><li>Global soil moisture product </li></ul>
  3. 3. Study area West Africa <ul><li>Why over West Africa ? </li></ul><ul><li>As shown by Koster et al. (2004), it is a region of strongest feedback of soil moisture on precipitation </li></ul><ul><li>Water monitoring is very important for population </li></ul><ul><li>Vegetation latitudinal gradient </li></ul><ul><li>Very interesting place to evaluate the sensitivity of SMOS to vegetation cover </li></ul><ul><li>Compared to higher microwaves bands from other sensors: </li></ul><ul><li>AMSR-E : 6.9 GHz, 10.7 GHz... </li></ul><ul><li> TMI : 10.7GHz,.... </li></ul><ul><li>Study area </li></ul><ul><li>5°S-20°E ; 20°N-20°W </li></ul>(Koster et al, 2004)
  4. 4. Study area Ground measurements <ul><li>AMMA </li></ul><ul><li>African Multidisciplinary Monsoon Analyses </li></ul><ul><li>Large observation network </li></ul><ul><li>AMMA-CATCH </li></ul><ul><li>3 sites located on latitudinal gradiant </li></ul><ul><li>Mali : semi-arid area </li></ul><ul><li>Niger : Moderate vegetation </li></ul><ul><li>Benin : Forest </li></ul><ul><li>Probe at 5 cm of depth </li></ul>Dry season Wet season Forest
  5. 5. Soil Moisture and Ocean Salinity Different products Soil moisture values from L2SM product Brightness temperatures from L1C product Temporal serie 17 – 23 March 2010
  6. 6. Comparison of Brightness Temperatures to passive microwaves sensors AMSR-E and TMI Spatial Acqu. Product Band Repere Angle resol. time used SMOS L / 1.4 XY multi 43km 6:30 L1C AMSR-E C / 6.9 HV 55° 56km 1:30 L3 V06 TMI X / 10.7 HV 52.8° 50km flex 1B11 <ul><li>Several passive microwaves sensors </li></ul><ul><li>Sensitivity to soil moisture variations is optimal on L-band </li></ul><ul><li>Soil moisture products are provided </li></ul><ul><li>based on these sensors </li></ul><ul><li>Comparison of TB from SMOS </li></ul><ul><li>to ones from other passive </li></ul><ul><li>microwaves sensors </li></ul><ul><li>AMSR-E at 6.9 GHz </li></ul><ul><li>TMI at 10.7 GHz </li></ul>But angle, time of overpass, frame... are not the same !
  7. 7. Comparison of Brightness Temperatures Compare similar information <ul><li>L1C product at antenna frame </li></ul><ul><li>SMOS : multiangular information </li></ul><ul><li>Angle information : TB translated in HV polarisation (surface frame) </li></ul><ul><li>Observation angle used = 55° obtained by TB interpolation </li></ul><ul><li>-> only frequence and acquisition time differ between the satellites </li></ul>8 May
  8. 8. Comparison of Brightness Temperatures Compare similar information <ul><li>L1C product at antenna level repere </li></ul><ul><li>SMOS : multiangular information </li></ul><ul><li>Angle information : TB translated in HV polarisation (surface coordinate frame) </li></ul><ul><li>Observation angle used = 55° obtained by TB interpolation </li></ul><ul><li>-> only frequence and acquisition time differ between the satellites </li></ul>
  9. 9. Comparison of Brightness Temperatures Polarisation ratio maps <ul><li>Vegetation latitudinal gradient </li></ul><ul><li>3 May 2010 </li></ul><ul><li>All PR increase for both main patches </li></ul><ul><li>Sensitivivity of AMSR-E is very low </li></ul><ul><li>SMOS PR variations at low latitudes </li></ul>AMSR-E 6.9GHz SMOS 1.4GHz TMI 10.7GHz
  10. 10. Comparison of Brightness Temperatures Polarisation ratio maps <ul><li>Sensitivity </li></ul><ul><li>12 May 2010 </li></ul><ul><li>All PR increase for both main patches </li></ul><ul><li>SMOS is the most accurate </li></ul><ul><li>SMOS records small patchs </li></ul>AMSR-E 6.9GHz SMOS 1.4GHz TMI 10.7GHz
  11. 11. Comparison of Brightness Temperatures Polarisation ratio maps <ul><li>Vegetation cover </li></ul><ul><li>8 June 2010 </li></ul><ul><li>Senegal / Gambia </li></ul><ul><li>Forest </li></ul><ul><li>SMOS sensitivity clearly hihgest </li></ul>AMSR-E 6.9GHz SMOS 1.4GHz TMI 10.7GHz
  12. 12. Temporal variations of brightness temperatures <ul><li>Mali </li></ul><ul><li>15.345°N -1.479°E </li></ul><ul><li>Mean value of TB is similar for all sensors </li></ul><ul><li>SMOS shows higher variability </li></ul><ul><li>Precipitation must be confirmed </li></ul><ul><li>Niger </li></ul><ul><li>13.645°N 2.63°E </li></ul><ul><li>Results are similar to those of </li></ul><ul><li>Mali </li></ul><ul><li>To confirm after vegetation has grown </li></ul><ul><li>Benin </li></ul><ul><li>9.685°N 1.65°E </li></ul><ul><li>H and V polarisation are very close for AMSR-E and TMI </li></ul><ul><li>Temporal dynamic is visible on SMOS H polarisation </li></ul>Comparison of Brightness Temperatures May June
  13. 13. Temporal variations of the polarisation ratio <ul><li>Mali </li></ul><ul><li>15.345°N -1.479°E </li></ul><ul><li>AMSR-E is very constant </li></ul><ul><li>Small variations for TMI </li></ul><ul><li>larger range for SMOS PR </li></ul><ul><li>Precipitation must be confirmed </li></ul><ul><li>Niger </li></ul><ul><li>13.645°N 2.63°E </li></ul><ul><li>Small variations for AMSR-E and TMI </li></ul><ul><li>Amplitude is highest for SMOS PR </li></ul><ul><li>Benin </li></ul><ul><li>9.685°N 1.65°E </li></ul><ul><li>PR is very low and without dynamic for AMSR-E and TMI </li></ul><ul><li>Temporal dynamic is still visible on SMOS polarisation ratio </li></ul>Comparison of Brightness Temperatures May June
  14. 14. Soil moisture product validation Soil moisture products based on microwave sensors <ul><li>5 soil moisture products was compared </li></ul><ul><li>on Sahelian area during 2005-2006 </li></ul><ul><li>Overestimation during the dry season </li></ul><ul><li>Vegetation impact </li></ul><ul><li>Temporal variation </li></ul>Gruhier et al, 2009, HESS <ul><li>– AMSR-E / NSIDC (L05) </li></ul><ul><li>– AMSR-E / VUA </li></ul><ul><li>– TMI / VUA </li></ul><ul><li>O ERS / CETP </li></ul><ul><li>+ ERS / TUW </li></ul><ul><li>Ground station </li></ul>2005-2006
  15. 15. Soil moisture product validation Is SMOS better ? <ul><li>Ground measurement not yet available </li></ul><ul><li>Similar condition every year </li></ul><ul><li>First idea </li></ul><ul><li>Ground validation on this site will be done as soon as possible </li></ul>Gruhier et al, 2009, HESS <ul><li>– AMSR-E / NSIDC (L05) </li></ul><ul><li>– AMSR-E / VUA </li></ul><ul><li>– TMI / VUA </li></ul><ul><li>O ERS / CETP </li></ul><ul><li>+ ERS / TUW </li></ul><ul><li>Ground station </li></ul>2005-2006
  16. 16. Soil moisture product validation Is SMOS better ? <ul><li>Ground measurement not yet available </li></ul><ul><li>Similar condition every year </li></ul><ul><li>First idea </li></ul><ul><li>Ground validation on this site will be done as soon as possible </li></ul><ul><li>-> SMOS provides realistics values </li></ul>Gruhier et al, 2009, HESS <ul><li>– AMSR-E / NSIDC (L05) </li></ul><ul><li>– AMSR-E / VUA </li></ul><ul><li>– TMI / VUA </li></ul><ul><li>O ERS / CETP </li></ul><ul><li>+ ERS / TUW </li></ul><ul><li>Ground station </li></ul>2005-2006 <ul><li>Jan-Mar 2010 </li></ul><ul><li>-o- SMOS </li></ul>
  17. 17. Soil moisture product validation Ground validation in Niger <ul><li>Ground measurements just available </li></ul><ul><li>on Niger site </li></ul><ul><li>SMOS : L2SM </li></ul><ul><li>Ground station: Niger </li></ul><ul><li>Time period: May – June </li></ul>
  18. 18. Soil moisture product validation SMOS/NSIDC product comparison in Niger <ul><li>Ground measurements and soil moisture products </li></ul><ul><li>SMOS: L2SM </li></ul><ul><li>AMSR-E: NSIDC V06 </li></ul><ul><li>Ground station: Niger </li></ul><ul><li>Time period: May – June </li></ul>
  19. 19. Conclusion of this preliminary study <ul><li>West Africa </li></ul><ul><li>A very interesting place to evaluate SMOS soil moisture product </li></ul><ul><li>A lot of soil and vegetation conditions </li></ul><ul><li>Intercomparison </li></ul><ul><li>Brightness temperature were compared in very similar condition (angle, polarisation...) </li></ul><ul><li>SMOS sensitivity is visible in case of vegetation and low increase of SM </li></ul><ul><li>Monsoon period will be a crucial validation period on sahelian area as both soil moisture and vegetation increase at the same time </li></ul><ul><li>NSIDC Level 3 data show a decrease of the Tb range? -> Use NSIDC Level 2 </li></ul><ul><li>Comparison with other soil moisture products </li></ul><ul><li>Preliminary results are really promising </li></ul><ul><li>Coimparison will have to be performed again (same time perid) </li></ul><ul><li>Ground validation </li></ul><ul><li>Ground validation is a crucial issue </li></ul><ul><li>Will be done when data is available </li></ul>
  20. 20. SMOS L-Band Brightness Temperatures Compared to Other Passive Microwaves Sensors over West Africa Area C. GRUHIER (1), Y. KERR (1), F. CABOT (1), A. MIALON (1), T. PELLARIN (2), P. DE ROSNAY (3), M. GRIPPA (4) [email_address] (1) CESBIO Toulouse France (2) LTHE Grenoble France (3) ECMWF Reading UK (4) LMTG Toulouse France <ul><li>Introduction </li></ul><ul><li>Study area </li></ul><ul><li>Soil Moisture and Ocean Salinity </li></ul><ul><li>Comparison of Brightness Temperatures </li></ul><ul><li>Soil moisture product validation </li></ul><ul><li>Conclusion </li></ul>IGARSS Session SMOS 26 – 30 July 2010 Honolulu, Hawaii

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