Salinity retrieval with scale model antenna pattern

1
Salinity retrieval with scale model antenna
pattern

• S. Kim/F. Wentz
• Aquarius Workshop (GSFC)
• 2008.03

2
Tb2 retrieval accuracy scale model (ascending)
Simple Faraday correction before additional
correction ?TB2/2 in Kelvin 2001 Solar
flux 2003 day 303 (IRI 2001 TEC) error reaches
/- 3-4K
Faraday angle
After
3
Tb2 retrieval scale-model (descending)
Before additional correction error reaches
-2K
Faraday angle
After
4
Scale model Tb1 retrieval accuracy (ascending)
Before additional Faraday correction
After
5
Scale model Tb1 descending
Before additional correction
After
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?Tb2 (with scale model) Faraday rotation

• ?Tb2 is strongly related to Faraday rotation
• (theoretical model ?Tb2 is offset by 1.5K simple
  correction T2 ?(T22T32))

Ascending horn 1 descending
K
latitude
latitude
Theoretical model
Scale model
Faraday angle
Faraday off Simple correction
Faraday off Simple correction
Faraday On Simple correction
Faraday On Simple correction
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Scale model antenna Stokes matrix (modified)

• scale model antennas off-diagonal term is 10-40
  times larger than theoreticals

theoretical antenna IHORN 1 0.9777995 0.0222005 0.0018323 0.0000360 0.0236619 0.9763381 -0.0016604 -0.0001937 -0.0012777 0.0011429 0.9584791 0.0017800 -0.0003209 -0.0001290 0.0001374 0.9443555 IHORN 2 0.9698600 0.0301399 -0.0027432 -0.0008946 0.0281496 0.9718504 0.0045488 -0.0004253 -0.0016207 0.0014077 0.9382428 0.0007672 0.0001413 -0.0006906 -0.0013847 0.9365401 IHORN 3 0.9659594 0.0340406 0.0014531 0.0007880 0.0334903 0.9665097 -0.0021459 -0.0001634 -0.0014786 0.0013045 0.9091309 -0.0004642 0.0000453 0.0003553 -0.0006897 0.9228344
scale model antenna HORN 1(n1) 0.9853075 0.0168026 -0.0195433 -0.0085144 0.0154680 0.9870461 0.0065521 0.0043823 -0.0018744 -0.0224793 0.9034507 -0.2914306 0.0063599 -0.0261359 0.2846981 0.9142451 HORN 2(p0) 0.9793472 0.0251813 -0.0082843 -0.0003378 0.0222499 0.9820560 -0.0088156 -0.0069168 0.0027088 -0.0392866 0.9340240 0.0511001 -0.0127451 0.0026349 -0.0496169 0.9496149 HORN 3(p1) 0.9736289 0.0336871 -0.0206253 -0.0046420 0.0273845 0.9800099 0.0076234 0.0009958 0.0049451 -0.0272600 0.8377592 -0.3615281 0.0066785 -0.0258146 0.3477410 0.8623706
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Scale model antenna Stokes matrix (classical)
theoretical antenna IHORN 1 1.0000000 0.0000000 0.0001719 0.0002297 0.0000000 0.9541376 0.0034927 0.0002297 -0.0000674 -0.0012103 0.9584791 0.0002297 -0.0000960 -0.0002249 0.0001374 0.9443555 IHORN 2 0.9999999 -0.0000000 0.0018056 -0.0004693 -0.0000000 0.9417105 -0.0072920 -0.0004693 -0.0001065 -0.0015142 0.9382428 -0.0004693 0.0004160 -0.0002746 -0.0013847 0.9365401 IHORN 3 1.0000000 0.0000000 -0.0006928 0.0009514 0.0000000 0.9324691 0.0035990 0.0009514 -0.0000870 -0.0013916 0.9091309 0.0009514 -0.0001550 0.0002003 -0.0006897 0.9228344
scale model antenna HORN 1(n1) 1.0023122 -0.0002020 -0.0129912 -0.0128967 -0.0002020 0.9700415 -0.0260954 -0.0128967 -0.0121768 0.0103024 0.9034507 -0.0128967 0.0162479 -0.0098880 0.2846981 0.9142451 HORN 2(p0) 1.0044172 0.0001113 -0.0170999 0.0065790 0.0001113 0.9569861 0.0005313 0.0065790 -0.0182889 0.0209977 0.9340240 0.0065790 -0.0076900 -0.0050551 0.0496169 0.9496149 HORN 3(p1) 1.0073552 -0.0000392 -0.0130019 -0.0056378 -0.0000392 0.9462836 -0.0282487 -0.0056378 -0.0111575 0.0161026 0.8377592 -0.0056378 0.0162465 -0.0095681 0.3477410 0.8623706
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Errors in Faraday correction
TA

• For uniform gain, no coupling, simple Faraday
  correction gives

TBR

• With coupling ( based on Le Vine et al 07)

ionosphere
TAtoa
TB
TBtoa
atmosphere

• The simple correction would produce

10
Additional Faraday correction

• No exact way to deconvolve the Faraday effect
  because of 4pi integration
• The additional correction is applied after APC
  (antenna pattern correction, A-matrix approach)

constant value for Tb1/Tb2 10,7,4 for
horn1,2,3 ?f (Faraday angle) is estimate as
0.5atan(Ta3/Ta2)
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Performance of additional correction for Tb2
Faraday off
Faraday On Simple correction
Faraday On Additional Correction
Land fraction
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Performance of additional correction for Tb1
Faraday off
Faraday On Simple correction
Faraday On Additional Correction
Land fraction
13
salinity retrieval accuracy after additional
correction
Ascending
Descending
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salinity retrieval scale model

• Scale model retrieval meets the SSS retrieval
  requirement
• Optimal case (SST gt 10C), land fraction lt 1e-3,
  but with the strongest Faraday rotation effect of
  a year and the strong solar effect

With scale model antenna pattern
?SSS(psu,6sec) mean std dev
Inner horn -0.005 0.23
Middle horn 0.054 0.21
Outer horn 0.019 0.21
With theoretical antenna pattern
?SSS (9sec) mean std dev
Inner horn -0.006 0.14
Middle horn -0.013 0.13
Outer horn -0.017 0.12
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salinity retrieval scale model

• All SST and land fraction lt 1e-3

With scale model antenna pattern
?SSS(psu) Mean std dev
Inner horn 0.013 0.44
Middle horn -0.032 0.44
Outer horn 0.052 0.41
With theoretical antenna pattern
?SSS mean std dev
Inner horn -0.007 0.28
Middle horn -0.010 0.27
Outer horn -0.016 0.26
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Practical considerations

• We dont know antenna pattern Faraday angle
• But these may be estimated
• By trial and error, determine Re(Gg)/G2
• -0.014, -0.018, -0.012 empirical
• -0.013, -0.019, -0.012 from scale-model pattern
• Faraday angle 0.5atan(ta3/ta2)
• Truth Faraday angle (forward simulation) works
  slightly better than 0.5atan()
• Nominal values of Tb1, Tb2 are ok

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Summary

• Simulation of salinity retrieval is performed
  using the scale model antenna pattern
• Simple correction of the Faraday effect is not
  sufficient, leaving up to 3-4K error in TB2
  retrieval (in worst-case Faraday condition)
• Additional Faraday correction is implemented
• Now TB1 and TB2 may be retrieved with less than
  0.15K error
• salinity may be retrieved with an accuracy better
  than 0.2psu.