FR2-T04-5_A_synergy_between_smos_and_aquarius.ppt

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FR2-T04-5_A_synergy_between_smos_and_aquarius.ppt

  1. 1. A synergy between SMOS & AQUARIUS: resampling SMOS maps at the resolution and incidence of AQUARIUS Eric A NTERRIEU , Yann K ERR , François C ABOT , Gary L AGERLOEF and David L E V INE
  2. 2. <ul><li>ESA mission for global monitoring of surface Soil Moisture and Ocean Salinity from space. </li></ul>SMOS <ul><li>1 synthetic aperture imaging radiometer </li></ul><ul><ul><li>L-band 1.413 GHz </li></ul></ul><ul><ul><li>69 antennas/receivers </li></ul></ul><ul><ul><li>diluted apertures (6.75 m) </li></ul></ul><ul><li>launched November 2 nd 2009 </li></ul><ul><li>http://www.esa.int/smos </li></ul>1
  3. 3. <ul><li>Partnership between NASA and CONAE for monitoring Sea Surface Salinity from space. </li></ul>AQUARIUS <ul><li>3 radiometers (+ 1 scatterometer) </li></ul><ul><ul><li>L-band 1.413 GHz </li></ul></ul><ul><ul><li>parabolic reflector, 3 feed horns </li></ul></ul><ul><ul><li>filled aperture (2.5 m) </li></ul></ul><ul><li>launched June 10 th 2011 </li></ul><ul><li>http://www.nasa.gov/aquarius </li></ul>2
  4. 5. AQUARIUS in SMOS
  5. 6. Why resampling? <ul><li>The spatial resolution achieved by SMOS is always smaller than the footprint of any of the 3 beams of AQUARIUS radiometers. </li></ul><ul><li>SMOS and AQUARIUS do not share the same sampling grids . </li></ul><ul><li>There is a need for resampling the temperature maps provided by SMOS down to the ground resolution of AQUARIUS beams so that a synergy between both missions can be properly set. </li></ul>3
  6. 7. How to interpolate? <ul><li>Resampling: discrete inverse Fourier transform </li></ul><ul><ul><li>only 1396 terms in the sum ( band-limited reconstruction… ) </li></ul></ul><ul><ul><li>does not introduce any interpolation artifact </li></ul></ul><ul><li>Resampling + Windowing: filter Gibbs effects </li></ul>4 T(  ,  ) =  T( u , v ) e +2j  ( u  + v  ) u , v  H  T (  ,  ) =  W( u , v ) T( u , v ) e u , v  H +2j  ( u  + v  ) w  
  7. 8. Kaiser window: 1 parameter s <ul><li>Kaiser windows are widely used for filtering out Gibbs effects. </li></ul><ul><li>Parameter   0 and constant over all the frequency coverage H (  is the radial distance normalized to the circumscribed circle). </li></ul><ul><li>For  = 0, the Kaiser window reduces to the rectangle window (no tapering). </li></ul>5 u v    = 1 W( u , v ) = I 0 (  ) I 0 (   1    ² ) 
  8. 9. Kaiser window: 1 parameter s <ul><li>The shape of the synthesized PSF W(  ,  ) is controlled by the value of  : </li></ul> = 3  = 10 spatial domain W(  ,  ) 5 u v    = 1 W( u , v ) = I 0 (  ) I 0 (   1    ² )  Fourier domain W( u , v ) 
  9. 10. How to interpolate? <ul><li>Resampling + Windowing: with a single window </li></ul><ul><ul><li>the same window is attached to each pixel (  ,  ) </li></ul></ul><ul><li>Resampling + Windowing: with multiple windows </li></ul><ul><ul><li>a unique window is attached to each pixel (  ,  ) </li></ul></ul>6 T (  ,  ) =  W( u , v ) T( u , v ) e u , v  H +2j  ( u  + v  ) w   T (  ,  ) =  W ( u , v ) T( u , v ) e   u , v  H +2j  ( u  + v  ) w  
  10. 11. Kaiser window: 3 parameters <ul><li>Value of  continuously depends on  with the aid of 3 parameters  1 ,  2 and  1 according to the linear relation: </li></ul><ul><li>It is possible to control the shape of W(  ,  ). </li></ul>7 u v  1  2    1  2  = 1   =  1 + (  2   1 )    1  2   1 W( u , v ) = I 0 (  ) I 0 (   1    ² ) 
  11. 12. Kaiser window: 3 parameters <ul><li>It is possible to control the shape of W(  ,  ): </li></ul> 1 = 0°  1 = 3  2 = 10  1 = 30°  1 = 10  2 = 3 spatial domain W(  ,  ) 7 W( u , v ) = I 0 (  ) I 0 (   1    ² )  u v  1  2    1  2  = 1  Fourier domain W( u , v ) 
  12. 13. Optimization of the multiple windows <ul><li>Characteristics of the footprint of AQUARIUS beams: </li></ul><ul><li>Resolution of SMOS is better than that of AQUARIUS for the same incidence angles (50-100 Km). </li></ul>8 incidence angle resolution a  b orientation  28.7° 37.8° 45.6° 1 94  76 Km 120  84 Km 156  96 Km  1 9.8°  15.3°  1 6.5° a b 
  13. 14. Optimization of the multiple windows <ul><li>Characteristics of the field of view of SMOS: </li></ul>9   @ instrument level cross track distance (Km) along track distance (Km) @ Earth surface
  14. 15. Optimization of the multiple windows <ul><li>Parameters  1 ,  2 and  1 can be optimized for degrading SMOS pixels down to the resolution of AQUARIUS at the Earth surface (non-linear optimization). </li></ul> 1  1  2 local azimuth angle (deg) local azimuth angle (deg) local azimuth angle (deg) 10  =  1 + (  2   1 )    1  2   1 W( u , v ) = with I 0 (  ) I 0 (   1    ² ) 
  15. 16. Optimization of the multiple windows <ul><li>Non-linear optimization is an heavy task, precluding any real time application. </li></ul><ul><li>These curves are tabulated in such a way that a linear interpolation does not introduced an error larger than 0.01 Km ( a and b ) and 0.01° (  ) on the final ground resolution. </li></ul> 1  1  2 local azimuth angle (deg) local azimuth angle (deg) local azimuth angle (deg) 10
  16. 17. Concrete illustration <ul><li>Orbit 2010 June 6 th 10:56:31 to 11:50:33 </li></ul><ul><li>Step 1: </li></ul><ul><ul><li>T x and T y read from SMOS L1b file </li></ul></ul><ul><ul><li>and resampled at AQUARIUS resolution/incidence </li></ul></ul>T x @ 28,7° T x @ 37,8° T x @ 45,6° 11
  17. 18. Concrete illustration <ul><li>Orbit 2010 June 6 th 10:56:31 to 11:50:33 </li></ul><ul><li>Step 1: </li></ul><ul><ul><li>T x and T y read from SMOS L1b file </li></ul></ul><ul><ul><li>and resampled at AQUARIUS resolution/incidence </li></ul></ul>T y @ 28,7° T y @ 37,8° T y @ 45,6° 11
  18. 19. Concrete illustration <ul><li>Orbit 2010 June 6 th 10:56:31 to 11:50:33 </li></ul><ul><li>Step 2: </li></ul><ul><ul><li>geometric rotation angle read from SMOS L1c file (DGG) </li></ul></ul><ul><ul><li>and interpolated (LSQ) at AQUARIUS incidence </li></ul></ul>geometric @ 28,7° geometric @ 37,8° geometric @ 45,6° 12
  19. 20. Concrete illustration <ul><li>Orbit 2010 June 6 th 10:56:31 to 11:50:33 </li></ul><ul><li>Step 2: </li></ul><ul><ul><li>faraday rotation angle read from SMOS L1c file (DGG) </li></ul></ul><ul><ul><li>and interpolated (LSQ) at AQUARIUS incidence </li></ul></ul>faraday @ 28,7° faraday @ 37,8° faraday @ 45,6° 12
  20. 21. Concrete illustration <ul><li>Orbit 2010 June 6 th 10:56:31 to 11:50:33 </li></ul><ul><li>Step 3: </li></ul><ul><ul><li>T h and T v computed from T x and T y and rotation angles </li></ul></ul><ul><ul><li>and written in SMOS L1c file (DGG) </li></ul></ul>T h @ 28,7° T h @ 37,8° T h @ 45,6° 13
  21. 22. Concrete illustration <ul><li>Orbit 2010 June 6 th 10:56:31 to 11:50:33 </li></ul><ul><li>Step 3: </li></ul><ul><ul><li>T h and T v computed from T x and T y and rotation angles </li></ul></ul><ul><ul><li>and written in SMOS L1c file (DGG) </li></ul></ul>T v @ 28,7° T v @ 37,8° T v @ 45,6° 13
  22. 23. Conclusion <ul><li>How to resample the temperature maps retrieved from SMOS interferometric measurements down to the ground resolution and at the incidence angles of AQUARIUS. </li></ul><ul><li>Resampling procedure is fast, accurate and operational. </li></ul><ul><li>A synergy between SMOS and AQUARIUS can be set for the benefit of both missions. </li></ul>14

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