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

6. Tb2 (with scale model) & Faraday rotation • Tb2 is strongly related to Faraday rotation • (theoretical model Tb2 is offset by 1.5K; simple correction: T2 = (T22+T32)) 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

7. Scale model antenna Stokes matrix (modified) • scale model antenna’s off-diagonal term is 10-40 times larger than theoretical’s

8. Scale model antenna Stokes matrix (classical)

9. 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 T’B 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 0.5*atan(Ta3/Ta2)

11. Performance of additional correction for Tb2 Faraday off Faraday On Simple correction Faraday On Additional Correction Land fraction

12. 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

14. salinity retrieval: scale model • Scale model retrieval meets the SSS retrieval requirement • Optimal case (SST > 10C), land fraction < 1e-3, but with the strongest Faraday rotation effect of a year and the strong solar effect • With scale model antenna pattern • With theoretical antenna pattern

15. salinity retrieval: scale model • With scale model antenna pattern • All SST and land fraction < 1e-3 • With theoretical antenna pattern

16. Practical considerations • We don’t 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

17. 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.