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. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 1 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

3. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 2 Validation of TMR MGDRB 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). 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.

4. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 3 Daily Averages of TMR vs. SSMI and TMI TMR from MGDRB Systematic yaw state errors distinct in daily averages. TMR from Replacement Product Yaw state errors removed.

5. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 4 Validation of JMR Version 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. 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.

6. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 5 Scatter of JMR versus ECMWF JMR from GDRBJMR 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.

7. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 6 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. Temporal variation of standard deviations of recalibrated TMR and JMR very consistent at 3 mm. –Random noise ~ 2mm.

8. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 7 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.

9. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 8 TMR versus JMR Geographically 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.

10. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 9 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.

11. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 10 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.

12. BACKUP SLIDES

13. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 12 Senatosa TMR wetter or JMR drier between land masses.

14. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 13 Scatter of TMR(RP) vs JMR

15. March 14, 2007Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session SD/SB/BH/WL/VZ - 14 Mean Offsets w.r.t. Independent Measurements RadiometerSSMITMI Global GPS Island GPS Continental GPS TMR(MGDRB)2.44.3-5.8-0.4-8.2 TMR (RP)6.07.7-2.41.8-4.4 JMR(GDRB)3.22.61.7-1.81.1 JMR(Recal.)5.66.74.21.03.3 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.