Bruce Haines and Shailen Desai Jet Propulsion Laboratory, California Inst. of Tech., Pasadena CA

1. Monitoring Jason-1 and TOPEX/POSEIDON from a California Offshore Platform: Latest Results from the Harvest Experiment Bruce Haines and Shailen Desai Jet Propulsion Laboratory, California Inst. of Tech., Pasadena CA George Born University of Colorado, Boulder Steve Gill NOAA National Ocean Service, Silver Spring MD March 12–15, 2007 Ocean Surface Topography Science Team Meeting Hobart, Australia

2. Motivation • How do we best calibrate sea-level record at the 1 mm/level? • Geographically correlated errors in both the bias and rate • What are the sources of the errors? Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

3. Map of Harvest Vicinity NOAA BUOYS SCRIPPS BUOY HARVEST Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

4. HARVEST EXPERIMENT WVR (JPL) GPS ANTENNA (JPL) + 54 m MET SENSORS LASER SENSOR (CU) + 27 m EQUIP SHED (NEW VSAT DISH) Point Arguello, CA + 6 m BUBBLER2 (NOAA) BUBBLER1 (NOAA)

5. 14 Years of Continuous GPS Monitoring Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

6. Harvest Closure Analysis (SSH Bias) Nominal Models for Altimeter Leg in Closure Equation • Some extended analysis: • Examine retracked ALT-B data (cycles 290–365) • Revisit legacy data (Jason GDR-A and T/P MGDR) with new in situ models • Evaluate preliminary ITRF2005-based solutions for T/P, Jason-1 orbits and platform position Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

7. Long-Term Sea-Surface Height Bias Estimates Nominal (T/P: MGDR-B+TMR+GSFC TVG; Jason-1: GDR-B) Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

8. Long-Term Sea-Surface Height Bias Estimates Legacy Products (T/P MGDR; Jason GDR-A) Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

9. Calibration of Vertical Wet Path Delay at Harvest USING DATA FROM HARVEST GPS RECEIVERS Uncalibrated (MGDR TMR & GDR-A JMR) Calibrated (Repro. TMR & GDR-B JMR) Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

10. Jason-1 Calibration Phase: Formation Flight with TOPEX/Poseidon (Jan. – Aug. 2002) • Satellites trace out same ground track • Jason-1 leads T/P by 70 s (~400 km) • Presents unique opportunity to cross calibrate independent measurements systems. • Enables observation of the same spot on the ocean surface under nearly identical environmental and ocean conditions. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

11. Jason-1 Verification Phase: Dual Overflight Results Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

12. T/P (ALT-B) Retracked Data Relative Ku-Band Range During Jason-1 Verification Phase: (HORBIT – RKu)JASON — (HORBIT – RKu)TOPEX SSH Bias (ALT–B) for Repeat Cycles 290–365 (RGDR Release) Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

13. Harvest Summary • Jason-1 SSH biased (high) by 11 cm. • Contrasts with +15 cm bias in legacy (GDR-A) data at epoch (2002.0) • Jason-1 SSH drift (< 1 mm/yr) statistically insignificant • Contrasts with large –10 mm/yr drift in legacy (GDR-A) data • Re-calibrated JMR and improved POE responsible for improvement • T/P SSH biases small • < 1 cm bias for ALT-A, ALT-B at epoch • Poseidon-1 bias (–2 cm) slightly significant • Slight drifts (< 1–2 mm/yr) in T/P altimeter measurement systems • Questionable statistical significance from Harvest data alone • New TMR wet path delay correction stable • Remaining drift << 1 mm/yr • Slight residual drift in JMR–GPS • –2.6 mm/yr at Harvest; not observed in global GPS results (Desai et al.) • ITRF2005 will affect SSH stability estimates at 1 mm/yr level (preliminary). • Mostly from change in estimated platform position; orbit effect small at Harvest lat. • Mixed results for T/P retracked data • LSE comparable to nominal, but fewer overflight samples survive (high o). • High scatter for MAP estimates. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

14. Backup Slides Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

15. 110 142 174 110 142 174 (mm) (mm) Geographically Correlated ErrorsJason-1 — T/P SSH (Tandem Verification Phase) Harvest Corsica • Assumptions • Jason-1 GDR-B replaces GDR-A • New GSFC T/P orbit (GGM02C) replaces MGDR POE • Global TMR drift correction applied • Topex ALT-B retracked range NOT used (next step) ASC. TRACKS s = 16 mm DES. TRACKS s = 12 mm BASS STRAIT Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

16. Geographically Correlated Errors Remain SSH Bias: Harvest vs. Global Results Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

17. Calibration of Ionosphere Delay at Harvest USING DATA FROM JPL GIM SOLUTION Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

18. Jason-1 SSH Stability Estimates Jason-1 GDR (Ver. A) + GPS Orbit + GPS Orbit + GPS Wet Path Delay + GPS Orbit + Calibrated JMR data Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

19. Conditions at Harvest are Typical of Open Ocean Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

20. Periodicities in the Platform Height Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

21. Geographically Correlated Radial Orbit Error Rate GDR Orbit — JPL GPS: Radial Rate for Cycles 1–90 All Tracks Descending Tracks Ascending Tracks Corsica: Rate = –0.5 mm/yr Bass Strait: Rate = –4.9 mm/yr Harvest: Rate = –6.6 mm/yr –10 0 10 mm/yr Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

22. GPS Antenna Phase Center Variations • Postfit tracking residuals are binned by az/el (Hurst and Bar-Sever, 1998) • Both carrier phase and pseudorange • Resulting antenna PCV maps used in precise point positioning • Mitigate multipath and other systematic GPS errors • Maps reduce amplitude of residual annual signal from 5.5 mm to 3.6 mm Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

23. CU Laser Sea Level System Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

24. CU Laser Sea Level System • Installed on 12 m deck, upstream of platform legs. • In operation since March, 2002 (precise survey pending). • Data used to mitigate Digibub sea-state errors. • Agreement between NOAA and CU sea level (after removing sea-state effect) is ~1.7 cm. Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

25. CU Sea Level System Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

26. Error Budget: Bias Ocean Surface Topography Science Working Team Meeting Cal/Val Splinter Session

27. GLOBAL Mean = 159.0 mm s = 12.1 mm NORTH Mean = 160.0 mm s = 12.0 mm TROPICS Mean = 154.1 mm s = 10.7 mm SOUTH Mean = 164.6 mm s = 10.8 mm Jason-1 – T/P Sea Surface Height: Descending Tracks Formation Flying Phase Jason-1 GDR: Cycles 1–21 T/P MDGR + TMR Drift Correction: Cycles 344–364 mm

28. GLOBAL Mean = 160.0 mm s = 15.9 mm NORTH Mean = 148.1 mm s = 12.7 mm TROPICS Mean = 152.1 mm s = 11.4 mm SOUTH Mean = 172.5 mm s = 10.9 mm Jason-1 – T/P Sea Surface Height: Ascending Tracks Formation Flying Phase Jason-1 GDR: Cycles 1–21 T/P MDGR + TMR Drift Correction: Cycles 344–364 mm