1. 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA 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. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA ESA mission for global monitoring of surface Soil Moisture and Ocean Salinity from space. SMOS  1 synthetic aperture imaging radiometer  L-band 1.413 GHz  69 antennas/receivers  diluted apertures (6.75 m)  launched November 2 nd 2009  http://www.esa.int/smos 1

3. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Partnership between NASA and CONAE for monitoring Sea Surface Salinity from space. AQUARIUS  3 radiometers (+ 1 scatterometer)  L-band 1.413 GHz  parabolic reflector, 3 feed horns  filled aperture (2.5 m)  launched June 10 th 2011  http://www.nasa.gov/aquarius 2

4. 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA

5. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA AQUARIUS in SMOS

6. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Why resampling?  The spatial resolution achieved by SMOS is always smaller than the footprint of any of the 3 beams of AQUARIUS radiometers.  SMOS and AQUARIUS do not share the same sampling grids.  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. 3

7. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA How to interpolate?  Resampling: discrete inverse Fourier transform  only 1396 terms in the sum (band-limited reconstruction…)  does not introduce any interpolation artifact  Resampling + Windowing: filter Gibbs effects 4 T( ,  ) =  T(u,v) e +2j  (u  + v  ) u,v  Hu,v  H  T ( ,  ) =  W(u,v) T(u,v) e u,v  Hu,v  H +2j  (u  + v  ) w  

8. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Kaiser window: 1 parameters  Kaiser windows are widely used for filtering out Gibbs effects.  Parameter   0 and constant over all the frequency coverage H (  is the radial distance normalized to the circumscribed circle).  For  = 0, the Kaiser window reduces to the rectangle window (no tapering). 5 u v    = 1 = 1 W(u,v) = I0()I0() I0( 1² )I0( 1² ) 

9. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Kaiser window: 1 parameters  The shape of the synthesized PSF W( ,  ) is controlled by the value of  : 5 u v    = 1 = 1 W(u,v) = I0()I0() I0( 1² )I0( 1² )   = 3  = 10 spatial domain W( ,  ) Fourier domain W(u,v) 

10. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA How to interpolate?  Resampling + Windowing: with a single window  the same window is attached to each pixel ( ,  )  Resampling + Windowing: with multiple windows  a unique window is attached to each pixel ( ,  ) 6 T ( ,  ) =  W(u,v) T(u,v) e u,v  Hu,v  H +2j  (u  + v  ) w   T ( ,  ) =  W (u,v) T(u,v) e   u,v  Hu,v  H +2j  (u  + v  ) w  

11. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Kaiser window: 3 parameters  Value of  continuously depends on  with the aid of 3 parameters  1,  2 and  1 according to the linear relation:  It is possible to control the shape of W( ,  ). 7 u v 11 22   11 22  = 1 = 1   =  1 + (  2   1 )   1  1 2  12  1 W(u,v) = I0()I0() I0( 1² )I0( 1² ) 

12. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Kaiser window: 3 parameters  It is possible to control the shape of W( ,  ): 7 W(u,v) = I0()I0() I0( 1² )I0( 1² )   1 = 0°  1 = 3  2 = 10  1 = 30°  1 = 10  2 = 3 u v 11 22   11 22  = 1 = 1  spatial domain W( ,  ) Fourier domain W(u,v) 

13. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Optimization of the multiple windows  Characteristics of the footprint of AQUARIUS beams:  Resolution of SMOS is better than that of AQUARIUS for the same incidence angles (50-100 Km). 8 incidence angle resolution a  b orientation  28.7° 37.8° 45.6° 194  76 Km 120  84 Km 156  96 Km  19.8°  15.3°  16.5° a b 

14. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Optimization of the multiple windows  Characteristics of the field of view of SMOS: 9   @ instrument level cross track distance (Km) along track distance (Km) @ Earth surface

15. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Optimization of the multiple windows  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). 10 11 11 22 local azimuth angle (deg)  =  1 + (  2   1 )   1  1 2  12  1 W(u,v) = with I0()I0() I0( 1² )I0( 1² ) 

16. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Optimization of the multiple windows  Non-linear optimization is an heavy task, precluding any real time application.  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. 10 11 11 22 local azimuth angle (deg)

17. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Concrete illustration 11  Orbit 2010 June 6 th 10:56:31 to 11:50:33  Step 1:  T x and T y read from SMOS L1b file  and resampled at AQUARIUS resolution/incidence T x @ 28,7°T x @ 37,8°T x @ 45,6°

18. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Concrete illustration 11  Orbit 2010 June 6 th 10:56:31 to 11:50:33  Step 1:  T x and T y read from SMOS L1b file  and resampled at AQUARIUS resolution/incidence T y @ 28,7°T y @ 37,8°T y @ 45,6°

19. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Concrete illustration 12  Orbit 2010 June 6 th 10:56:31 to 11:50:33  Step 2:  geometric rotation angle read from SMOS L1c file (DGG)  and interpolated (LSQ) at AQUARIUS incidence geometric @ 28,7°geometric @ 37,8°geometric @ 45,6°

20. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Concrete illustration 12  Orbit 2010 June 6 th 10:56:31 to 11:50:33  Step 2:  faraday rotation angle read from SMOS L1c file (DGG)  and interpolated (LSQ) at AQUARIUS incidence faraday @ 28,7°faraday @ 37,8°faraday @ 45,6°

21. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Concrete illustration 13  Orbit 2010 June 6 th 10:56:31 to 11:50:33  Step 3:  T h and T v computed from T x and T y and rotation angles  and written in SMOS L1c file (DGG) T h @ 28,7°T h @ 37,8°T h @ 45,6°

22. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Concrete illustration 13  Orbit 2010 June 6 th 10:56:31 to 11:50:33  Step 3:  T h and T v computed from T x and T y and rotation angles  and written in SMOS L1c file (DGG) T v @ 28,7°T v @ 37,8°T v @ 45,6°

23. A synergy between SMOS & AQUARIUS… 2011 IEEE International Geoscience And Remote Sensing Symposium IGARSS’11  July 24-29, 2011  Vancouver, C ANADA Conclusion 14  How to resample the temperature maps retrieved from SMOS interferometric measurements down to the ground resolution and at the incidence angles of AQUARIUS.  Resampling procedure is fast, accurate and operational.  A synergy between SMOS and AQUARIUS can be set for the benefit of both missions.