FR2-T04-5_A_synergy_between_smos_and_aquarius.ppt

2011 IEEE International Geoscience And Remote Sensing SymposiumIGARSS’11 July 24-29, 2011 Vancouver, CANADA

A synergy between SMOS & AQUARIUS:resampling SMOS maps at the resolution

and incidence of AQUARIUS

Eric ANTERRIEU, Yann KERR, François CABOT, Gary LAGERLOEF and David LE VINE

A synergy between SMOS & AQUARIUS…


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 2nd 2009

http://www.esa.int/smos

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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 10th 2011

http://www.nasa.gov/aquarius

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AQUARIUS in SMOS



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.

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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

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T(,) = T(u,v) e+2j(u + v )u,v H

T (,) = W(u,v) T(u,v) eu,v H

+2j(u + v )w



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).

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u

v

= 1

W(u,v) = I0()

I0( 1² )



Kaiser window: 1 parameters The shape of the synthesized PSF

W(,) is controlled by the value of :

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u

v

= 1

W(u,v) = I0()

I0( 1² )

= 3 = 10

spatialdomainW(,)

FourierdomainW(u,v)



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 (,)

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T (,) = W(u,v) T(u,v) eu,v H

+2j(u + v )w

T (,) = W (u,v) T(u,v) e u,v H

+2j(u + v )w



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(,).

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u

v

1

2

1

2

= 1

= 1 + (2 1) 1

2 1

W(u,v) = I0()

I0( 1² )



Kaiser window: 3 parameters It is possible to control the shape

of W(,):

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W(u,v) = I0()

I0( 1² )

1 = 0°1 = 3

2 = 10

1 = 30° 1 = 102 = 3

u

v

1

2

1

2

= 1

spatialdomainW(,)

FourierdomainW(u,v)



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).

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incidenceangle

resolutiona b

orientation

28.7°37.8°45.6°

194 76 Km120 84 Km156 96 Km

19.8°15.3°16.5°

a b



Optimization of the multiple windows Characteristics of the field of view of SMOS:

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@ instrument level

cross track distance (Km)

alon

g tr

ack

dist

ance

(K

m)

@ Earth surface



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).

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1 12

local azimuth angle (deg) local azimuth angle (deg) local azimuth angle (deg)

= 1 + (2 1) 1

2 1W(u,v) = with

I0()I0( 1² )



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.

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1 12

local azimuth angle (deg) local azimuth angle (deg) local azimuth angle (deg)



Concrete illustration

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Orbit 2010 June 6th 10:56:31 to 11:50:33 Step 1:

Tx and Ty read from SMOS L1b file and resampled at AQUARIUS resolution/incidence

Tx @ 28,7° Tx @ 37,8° Tx @ 45,6°




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Tx and Ty read from SMOS L1b file and resampled at AQUARIUS resolution/incidence

Ty @ 28,7° Ty @ 37,8° Ty @ 45,6°




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geometric rotation angle read from SMOS L1c file (DGG) and interpolated (LSQ) at AQUARIUS incidencegeometric @ 28,7° geometric @ 37,8° geometric @ 45,6°




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faraday rotation angle read from SMOS L1c file (DGG) and interpolated (LSQ) at AQUARIUS incidence

faraday @ 28,7° faraday @ 37,8° faraday @ 45,6°




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Th and Tv computed from Tx and Ty and rotation angles and written in SMOS L1c file (DGG)

Th @ 28,7° Th @ 37,8° Th @ 45,6°




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Th and Tv computed from Tx and Ty and rotation angles and written in SMOS L1c file (DGG)

Tv @ 28,7° Tv @ 37,8° Tv @ 45,6°



Conclusion

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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.

FR2-T04-5_A_synergy_between_smos_and_aquarius.ppt

Documents

t hand t

t xand t yread

smos aquarius

smos l1c file dgg t

t xand t yand rotation

fourier domain w u

resolution of smos

smos l1c file dgg t