SMOS L2 Ocean Salinity Level 2 Ocean Salinity Using TEC estimated from Stokes 3 24 October 2012 ACRI-st, LOCEAN & ARGANS SMOS+polarimetry

SMOS L2 Ocean Salinity TEC may be estimated from A3 assuming Stokes 3 at ground level = 0 (ATBD from ACRI-st & LOCEAN) TEC has a high latitudinal gradient in descending orbits with an active sun: L1c snapshot TEC may be biased at high incidence angles, giving incorrect Faraday rotation angles Study impact of ‘better’ A3 TEC estimation for high TEC descending orbits 1-6 May 2012: construct OTT, use OTT in L2OS Nominally, L2OS retrieves TEC using median of L1c TEC grid point dwell measurements as prior; prototype L2OS v600 can use A3 TEC per measurement (& convergence algorithm adjusts mean TEC bias) Test the A3 TEC solution... Overview

SMOS L2 Ocean Salinity Estimates of TB fwd TEC sensitivity 20 south25 north Most sensitive TB is A3 at high incidence angles

SMOS L2 Ocean Salinity TB fwd TEC sensitivity Most sensitive TB is A3 No TEC retrieval possible: line-of-sight perpendicular to magnetic field

SMOS L2 Ocean Salinity Apply OTT & perform outlier detection: only use good TB Select A3 measurements with high incidence angles close to the track eg < xi < 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 A3 TEC methodology

SMOS L2 Ocean Salinity Example TEC retrieval Sensitivity of A3 to TEC along the swath Coast delta = A3 minus modelled A3 using L1c TEC

SMOS L2 Ocean Salinity Nominal OTT

SMOS L2 Ocean Salinity A3 TEC OTT A3 TEC interpolated at 450km along each measurement line-of-sight

SMOS L2 Ocean Salinity Nominal OTT std/ra

SMOS L2 Ocean Salinity A3 TEC OTT std/ra OTT corrected at high incidence angles in HH/VV & Stokes 3

SMOS L2 Ocean Salinity Nominal OTT & L2OS using L1cTEC

SMOS L2 Ocean Salinity OTT & L2OS using A3 TEC ~3% more retrievals, mostly at regions with high TEC gradient/peaks

SMOS L2 Ocean Salinity Delta = nominal minus A3 TEC Up to ±0.5 psu error in SSS where TEC is wrong (eg latitudes -25 & -50)

SMOS L2 Ocean Salinity A3 TEC compared with L1c TEC Why is L1cTEC different from A3 TEC?

SMOS L2 Ocean Salinity L2OS retrieved TEC using A3 OTT & A3 TEC prior Retrieved TEC shows L1c (& A3) TEC underestimated

SMOS L2 Ocean Salinity L2OS retrieved TEC using nominal OTT & L1c TEC prior Retrieved TEC matches A3 TEC better than L1c TEC

SMOS L2 Ocean Salinity OTT significantly corrected at high incidence angles in HH/VV & Stokes 3 Up to ±0.5 psu improvement/correction of retrieved salinity in high TEC regions Up to 4% increase in retrievals using A3 TEC for OTT & in L2OS Retrieved TEC matches A3 TEC better than L1c TEC Next: – evaluate impact on more orbits: low TEC gradient, ascending... – evaluate impact on retrieved salinity – compare to Argo... – determine how algorithm can be integrated into L2OS processor (OTTs are generated by forward model using L1c TEC, but this method requires OTTs to be applied before deriving A3 TEC) Conclusions