Validation of the TMR and JMR Wet Path delay Measurements using GPS, SSM/I, and TMI

1. Validation of the TMR and JMR Wet Path delay Measurements using GPS, SSM/I, and TMI Shailen Desai Shannon Brown Bruce Haines Wenwen Lu Victor Zlotnicki Jet Propulsion Laboratory, California Institute of Technology Ocean Surface Topography Science Working Team Meeting, March 14, 2007

2. Objective • Independent validation of wet path delay (WPD) measurements from Topex and Jason microwave radiometers. • SSM/I • Special Sensor Microwave Imager on Defense Meteorological Satellite Program (DMSP) satellites. • Available for duration of Topex/Poseidon and Jason-1 missions. • TMI • Tropical Rainfall Measuring Mission’s Microwave Imager. • Available 1998-present (T/P cycle 193 onwards). • Coastal GPS sites • 1-87 sites available for Topex/Poseidon (presently on original ground track only). • ~30 of 87 sites available for each cycle of Jason-1 mission. • Characterize: • Temporal stability • Scale errors • Geographically correlated errors Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

3. TMR Replacement Product • Released Dec 13, 2006. • Drift removed (< 0.05 mm/yr) • Yaw state dependence reduced to < 1 mm. • TMR RP is drier than TMR-MGDRB by ~ 3 mm. • TMR-GPS is biased ~-9 mm from TMR-SSMI and TMR-TMI. Validation of TMRMGDRB and Replacement Product • TMR from MGDRB • 0.8 mm/yr drift from cycle 30-240 • ~5mm peak-to-peak dependence on satellite attitude regime (yaw state). Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

4. TMR from Replacement Product • Yaw state errors removed. Daily Averages of TMR vs. SSMI and TMI • TMR from MGDRB • Systematic yaw state errors distinct in daily averages. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

5. Recalibration of JMR • In preparation for Version C GDRs. • Will be ~3mm drier than version B GDRs. • Scale error corrected. • JMR-ECMWF drift reduced to -0.25 mm/yr • May have contribution from < 2 mm shifts after cycle 136 and 179 safeholds. • Will be corrected in Version C. Validation of JMRVersion B and Ongoing Recalibration • JMR from GDRB • All 4 comparisons agree to within 3.2 mm. • Residual (< 3mm) yaw state dependence may remain after cycle 100. • JMR-ECMWF has a drift of -0.3 mm/year. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

6. Scatter of JMR versus ECMWF JMR from GDRB JMR from Ongoing Recalibration • Comparison to ECMWF suggests scale error of ~2% in JMR from Version B GDR. • Error consistent with known changes to pre-launch calbration coefficients. • Can be corrected by dividing JMR(GDRB) by 1.023 • JMR on version C GDRs will correct this error. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

7. Temporal variation of standard deviations of recalibrated TMR and JMR very consistent at 3 mm. • Random noise ~ 2mm. TMR versus JMR(Temporal Stability) • Attitude dependence evident in TMR (MGDRB). • Removed in TMR (RP). • TMR (RP) and JMR(Recal.) drier than TMR (MGDRB) and JMR(GDRB) by ~3 mm. • Effect of correcting scale error. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

8. Scatter of TMR vs JMR (GDRB) TMR(MGDRB) vs JMR(GDRB) TMR(RP) vs JMR(GDRB) • Significant reduction of outliers in TMR-JMR differences from recalibration and reprocessing of TMR. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

9. TMR versus JMRGeographically Correlated Differences • As previously shown, banding around continents in TMR-JMR differences. • Differences with island and continental GPS sites suggested TMR as source. • Still present in recalibrated TMR and JMR. • < 1 mm effect from 200 km out to open ocean. • -3.5 mm from 200 to 50 km. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

10. Average of Differences w.r.t. Independent Measurements • JMR comparisons to SSMI, TMI, and GPS statistically identical. • TMR comparisons to GPS are biased by ~ -9 mm versus SSMI and TMI. • Separation of GPS comparisons by island and continental sites shows large discrepancy for TMR, but not for JMR. • TMR likely dominant source for errors near continents. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

11. Summary • TMR recalibrated and reprocessed. • Provided as TMR Replacement Product (Dec. 13, 2006) • Provided on Topex Retracked GDRs. • Drift and yaw state effects corrected. • Coastal effect remains. • ~3.5 mm wetter as approaching coast from 200 km out. • JMR (GDRB) corrects large shifts observed in version A GDRs. • < 2mm shifts may be present after cycle 136 and 179 safeholds. • Will be corrected in Version C GDRs. • Scale error of ~2% present in JMR (GDRB) • Will be corrected in Version C GDRs. • Can be corrected by dividing JMR(GDRB) by 1.023. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

12. BACKUP SLIDES

13. Senatosa TMR wetter or JMR drier between land masses. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

14. Scatter of TMR(RP) vs JMR Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

15. Mean Offsets w.r.t. Independent Measurements • JMR comparisons to SSMI, TMI, and GPS statistically identical. • TMR comparisons to GPS are biased by ~ -9 mm versus SSMI and TMI. • Separation of comparisons to island and continental GPS shows large discrepancy for TMR, but not for JMR. • TMR likely dominant source for ~4 mm errors near continents. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session