FR3.L10.4: SMOS SOIL MOISTURE VALUES EVALUATION OVER SAHELIAN AREA
20
SMOS L-Band Brightness Temperatures Compared to Other Passive Microwaves Sensors over West Africa Area . GRUHIER (1), Y. KERR (1), F. CABOT (1), . MIALON (1), T. PELLARIN (2), P. DE ROSNAY (3), . GRIPPA (4) [email protected] (1) CESBIO Toulouse France (2) LTHE Grenoble France (3) ECMWF Reading UK (4) LMTG Toulouse France Introduction Study area Soil Moisture and Ocean Salinity Comparison of Brightness Temperatures Soil moisture product validation Conclusion IGARSS Session SMOS 26 – 30 July 2010 Honolulu, Hawaii
description
Transcript of FR3.L10.4: SMOS SOIL MOISTURE VALUES EVALUATION OVER SAHELIAN AREA
SMOS L-Band Brightness TemperaturesCompared 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)
(1) CESBIOToulouse
France
(2) LTHE Grenoble
France
(3) ECMWF Reading
UK
(4) LMTG Toulouse
France
Introduction Study area Soil Moisture and Ocean Salinity Comparison of Brightness Temperatures Soil moisture product validation Conclusion
IGARSSSession SMOS
26 – 30 July 2010Honolulu, Hawaii
Introduction
Scientific context
Why study soil moisture ? One of the most important variable which strongly influences the soil-vegetation-atmosphere fluxes.
How access to this information ? Ground measurements Remote sensing Modelling
Soil Moisture and Ocean Salinity Passive microwaves sensor in L-band Launched the 2th November 2009 Global soil moisture product
Study area
West Africa
Why over West Africa ? As shown by Koster et al. (2004), it is a region of strongest feedback ofsoil moisture on precipitation Water monitoring is very importantfor population
Vegetation latitudinal gradient Very interesting place to evaluate the sensitivity of SMOS to vegetation cover Compared to higher microwaves bands from other sensors:
AMSR-E : 6.9 GHz, 10.7 GHz... TMI : 10.7GHz,....
Study area 5°S-20°E ; 20°N-20°W
(Koster et al, 2004)
Study area
Ground measurements
AMMA African Multidisciplinary Monsoon Analyses Large observation network AMMA-CATCH 3 sites located on latitudinal gradiant
Mali : semi-arid area Niger : Moderate vegetation Benin : Forest
Probe at 5 cm of depth
Dry season Wet season Forest
Soil Moisture and Ocean Salinity
Different products
Soil moisture values from L2SM product
Brightness temperatures from L1C product
Temporal serie17 – 23 March 2010
Comparison of Brightness Temperatures
to passive microwaves sensors AMSR-E and TMI
Spatial Acqu. Product
Band Repere Angle resol. time used
SMOS L / 1.4XY multi 43km 6:30 L1CAMSR-E C / 6.9 HV 55° 56km 1:30 L3 V06TMI X / 10.7 HV 52.8° 50km flex 1B11
Several passive microwaves sensors Sensitivity to soil moisture variations is optimal on L-band Soil moisture products are provided based on these sensors
Comparison of TB from SMOS to ones from other passive microwaves sensors AMSR-E at 6.9 GHz TMI at 10.7 GHz
But angle, time of overpass, frame... are not the same !
Comparison of Brightness Temperatures
Compare similar information
L1C product at antenna frameSMOS : multiangular information Angle information : TB translated in HV polarisation (surface frame) Observation angle used = 55° obtained by TB interpolation
-> only frequence and acquisition time differ between the satellites
8 May
Comparison of Brightness Temperatures
Compare similar information
L1C product at antenna level repereSMOS : multiangular information Angle information : TB translated in HV polarisation (surface coordinate frame) Observation angle used = 55° obtained by TB interpolation
-> only frequence and acquisition time differ between the satellites
Comparison of Brightness Temperatures
Polarisation ratio maps
Vegetation latitudinal gradient 3 May 2010 All PR increase for both main patches Sensitivivity of AMSR-E is very low SMOS PR variations at low latitudes
AMSR-E 6.9GHz SMOS 1.4GHz
TMI 10.7GHz
Comparison of Brightness Temperatures
Polarisation ratio maps
Sensitivity 12 May 2010 All PR increase for both main patches SMOS is the most accurate SMOS records small patchs
AMSR-E 6.9GHz SMOS 1.4GHz
TMI 10.7GHz
Comparison of Brightness Temperatures
Polarisation ratio maps
Vegetation cover 8 June 2010 Senegal / Gambia Forest SMOS sensitivity clearly hihgest
AMSR-E 6.9GHz SMOS 1.4GHz
TMI 10.7GHz
Temporal variations of brightness temperatures
Mali 15.345°N -1.479°E Mean value of TB is similar for all sensors SMOS shows higher variability Precipitation must be confirmed
Niger 13.645°N 2.63°E Results are similar to those ofMali To confirm after vegetationhas grown
Benin 9.685°N 1.65°E H and V polarisation are very close for AMSR-E and TMI Temporal dynamic is visibleon SMOS H polarisation
Comparison of Brightness Temperatures
May June
Temporal variations of the polarisation ratio
Mali 15.345°N -1.479°E AMSR-E is very constant Small variations for TMI larger range for SMOS PR Precipitation must be confirmed
Niger 13.645°N 2.63°E Small variations for AMSR-E and TMI Amplitude is highest for SMOS PR
Benin 9.685°N 1.65°E PR is very low and without dynamic for AMSR-E and TMI Temporal dynamic is still visibleon SMOS polarisation ratio
Comparison of Brightness Temperatures
May June
Soil moisture product validation
Soil moisture products based on microwave sensors
5 soil moisture products was compared on Sahelian area during 2005-2006 Overestimation during the dry season Vegetation impact Temporal variation
Gruhier et al, 2009, HESS
– AMSR-E / NSIDC (L05)
– AMSR-E / VUA – TMI / VUA O ERS / CETP + ERS / TUW Ground station
2005-2006
Soil moisture product validation
Is SMOS better ?
Ground measurement not yet available Similar condition every year First idea Ground validation on this site will be done as soon as possible
Gruhier et al, 2009, HESS
– AMSR-E / NSIDC (L05)
– AMSR-E / VUA – TMI / VUA O ERS / CETP + ERS / TUW Ground station
2005-2006
Soil moisture product validation
Is SMOS better ?
Ground measurement not yet available Similar condition every year First idea Ground validation on this site will be done as soon as possible→ SMOS provides realistics values
Gruhier et al, 2009, HESS
– AMSR-E / NSIDC (L05)
– AMSR-E / VUA – TMI / VUA O ERS / CETP + ERS / TUW Ground station
2005-2006
Jan-Mar 2010 -o- SMOS
Soil moisture product validation
Ground validation in Niger
Ground measurements just availableon Niger site SMOS : L2SM Ground station: Niger Time period: May – June
Soil moisture product validation
SMOS/NSIDC product comparison in Niger
Ground measurements and soil moisture products SMOS: L2SM AMSR-E: NSIDC V06 Ground station: Niger Time period: May – June
Conclusion
of this preliminary study
West Africa A very interesting place to evaluate SMOS soil moisture product A lot of soil and vegetation conditions
Intercomparison Brightness temperature were compared in very similar condition (angle, polarisation...) SMOS sensitivity is visible in case of vegetation and low increase of SM Monsoon period will be a crucial validation period on sahelian area as both soil moisture and vegetation increase at the same time NSIDC Level 3 data show a decrease of the Tb range? → Use NSIDC Level 2
Comparison with other soil moisture products Preliminary results are really promising Coimparison will have to be performed again (same time perid)Ground validation Ground validation is a crucial issue Will be done when data is available
SMOS L-Band Brightness TemperaturesCompared 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)
(1) CESBIOToulouse
France
(2) LTHE Grenoble
France
(3) ECMWF Reading
UK
(4) LMTG Toulouse
France
Introduction Study area Soil Moisture and Ocean Salinity Comparison of Brightness Temperatures Soil moisture product validation Conclusion
IGARSSSession SMOS
26 – 30 July 2010Honolulu, Hawaii
