Level 2 Ocean Salinity

1. Level 2 Ocean Salinity 16-17 May 2013 A3TEC

2. TEC from Stokes 3 • Apply OTT, perform outlier detection, un-apply OTT: only use good TB • Select A3 measurements with high incidence angles close to the track • eg -0.025 < xi < 0.025 and 0.15 < eta < 0.2 • Compute latitude where line of sight cross altitude of 450 km • Estimate TEC for each A3 value using the forward model & L1c TEC as prior • Use a latitudinal slippery window to detect & remove A3 TEC outliers, • estimate mean & error by latitude

3. TEC from Stokes 3 • Status • Algorithm specified, breadboard in Matlab cross-verified with v610 implementation • A3TEC used to generate OTT (via AUX_DTBXY), and for retrievals • computed AUX_DTBXY deltaTBs are for future OTT generation • OS retrievals use pre-computed OTT and TEC derived from current orbit • Tests performed with descending and ascending orbits • Open questions • How to handle cross-track TEC variation? • Why do we need to retrieve TEC in the main convergence loop after retrieving A3TEC? • What should the prior error be for main loop TEC retrieval? • Test plan • Process one month (May 2011?) and verify improvements using Argo/ISAS • Perform in parallel to OTTPP verification

4. L2OS implementation algorithm • apply measurement selection • if computing deltaTBs for AUX_DTBXY/OTTPP //eg ROI = South Pacific • if computing TEC from Stokes3 //AUX_CNFOSF switch_a3tec • retrieve TEC & OTT deltaTBs using Stokes3 //do not apply AUX_OTTxF • compute A3TEC at 450 km, interpolate & compute Faraday rotation • for model = 1 to 3 • compute deltaTBs • write AUX_DTBXY • if computing TEC from Stokes3 //AUX_CNFOSF switch_a3tec • apply model 1 OTTs • retrieve TEC using Stokes3 //do not retrieve OTT at the same time • un-apply model 1 OTTs • compute A3TEC at 450 km, interpolate & compute Faraday rotation • compute forward model 1 BTs • apply measurement selection

5. Descending orbit, high TEC gradient L1cTEC & A3TEC tecu tecu latitude latitude L1PP v600 20110505T040402 Cross-verification between Matlab breadboard & v610: delta = breadboard – v610

6. Descending orbit, high TEC gradient Faraday rotation per measurement along track (±0.2 in xi) for a single snapshot (ID 79013123) where there is a large difference (up to 30 tecu) between L1cTEC and A3TEC: delta up to 8 degrees. Faraday rotation angle Latitude L1PP v600 20110505T040402

7. Descending orbit, high TEC gradient A3TEC L1cTEC L1PP v600 20110505T040402

8. Descending orbit, high TEC gradient A3TEC L1cTEC L1PP v600 20110505T040402 large difference (up to 5 K at large incidence angles)

9. A3TEC minus L1cTEC Sensitivity to TEC: left/right sign change explains HH/VV sign change HH & VV Stokes 3 & 4

10. Descending orbit, high TEC gradient delta TB (K) Target to sat zenith angle 20110505T040402 GPID 9189693 (-14.7, 161.5) (xi 0.001, eta -0.4 to +0.3) Target to sat zenith angle delta TB (K) Forward model with A3TEC closer to L1c TBs than the model using L1cTEC at high incidence angles (as expected), in H pol & Stokes 3

11. Ascending orbit L1cTEC & A3TEC tecu Ascending orbit with low TEC & low TEC gradient – noisy A3 TEC retrieval, but good match with L1c latitude L1PP v600 20100802T153815

12. Impact on salinity L1OP v504 20110501T000016: high TEC gradient L1c TEC SSS1 & A3TEC SSS1 & L1cTEC delta = A3TEC – L1cTEC