monitoring jason-1 and topex/poseidon from a california offshore platform: latest results from the...

Monitoring Jason-1 and TOPEX/POSEIDON from a

California Offshore Platform: Latest Results from the

Harvest Experiment

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

George BornUniversity of Colorado, Boulder

Steve GillNOAA National Ocean Service, Silver Spring MD

March 12–15, 2007

Ocean Surface Topography Science Team Meeting

Hobart, Australia

March 12-15, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

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?

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Global Sea Level from T/P and Jason-1: UNCALIBRATED Record for 1992—2006

Mean Global SSH (mm)

T/P: ALT A SideRate = +2.7 mm/yr

T/P: ALT B SideRate = +3.9 mm/yr

Jason-1: Old (A) GDR Rate = –1.9 mm/yr

143 mm13 mm

Jason-1: New (B) GDRRate = +3.8 mm/yr

26 mm


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HarvestLos Angeles

Map of Harvest Vicinity

HARVEST

NOAABUOYS

SCRIPPSBUOY

GPS ANTENNA (JPL)WVR (JPL)

BUBBLER1 (NOAA)

BUBBLER2 (NOAA)

HARVEST EXPERIMENT

EQUIP SHED(NEW VSAT DISH)

MET SENSORS

Point Arguello, CA

+ 54 m

+ 27 m

+ 6 m

LASERSENSOR

(CU)


14 Years of Continuous GPS Monitoring


Harvest Closure Analysis (SSH Bias)

Model Jason-1 TOPEX/POSEIDON

Orbital height GDR-B POE (SLR + Doris + GPS) GSFC TVG POE (for RGDR)

Range Ku (GDR-B) Ku (MGDR)

Wet troposphere Brown et al. repro. (GDR-B) Brown et al. repro. (for RGDR)

Dry troposphere ECMWF* (GDR-B) ECMWF (MGDR)

Ionosphere Ku-Band (GDR-B) ALT/Ku, SSALT/DORIS (MGDR)

Sea-state bias Labroue et al. (GDR-B) Gaspar et al. (MGDR)

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


Long-Term Sea-Surface Height Bias EstimatesNominal (T/P: MGDR-B+TMR+GSFC TVG; Jason-1: GDR-B)

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LAD Drift(mm/yr)

LSQ Drift(mm/yr)

LAD Bias(mm)

LSQ Bias(mm)EpochAltimeter

+3.5+1.4 ± 1.5+14.4–2.6 ± 9.52002.0TOPEX-A–2.5–0.4 ± 2.7–34.4–19.6 ± 17.02002.0POSEIDON-1–4.0–1.5 ± 3.3–7.5–4.9 ± 5.32002.0TOPEX-B–0.7+0.3 ± 2.0+119.4+114.2 ± 6.42002.0JASON (GDR-B)


Long-Term Sea-Surface Height Bias EstimatesLegacy Products (T/P MGDR; Jason GDR-A)

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LAD Drift(mm/yr)

LSQ Drift(mm/yr)

LAD Bias(mm)

LSQ Bias(mm)EpochAltimeter

+0.3–0.7 ± 1.5+4.8–1.8 ± 9.62002.0TOPEX-A–4.4–2.3 ± 3.0–38.9–29.7 ± 18.52002.0POSEIDON-1–0.2+1.1 ± 3.4–0.4+2.4 ± 5.32002.0TOPEX-B–7.1–10.2 ± 2.9+146.1+151.8 ± 6.32002.0JASON (GDR-B)


Calibration of Vertical Wet Path Delay at HarvestUSING DATA FROM HARVEST GPS RECEIVERS

Uncalibrated(MGDR TMR &GDR-A JMR)

Calibrated(Repro. TMR &GDR-B JMR)

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TMR – GPS Bias (2002.0) = +5.3 ± 1.0 mm, Rate = –0.8 ± 0.2 mm/yrJMR – GPS Bias (2002.0) = +6.2 ± 1.9 mm, Rate = –4.8 ± 0.9 mm/yr

TMR – GPS Bias (2002.0) = +2.4 ± 1.0 mm, Rate = –0.2 ± 0.2 mm/yrJMR – GPS Bias (2002.0) = +4.2 ± 1.6 mm, Rate = –2.6 ± 0.5 mm/yr


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.


Jason-1 Verification Phase: Dual Overflight Results

05 01 0 01 5 02 0 02 5 0051 01 52 02 5J a s o n -1 — T /P R e la tiv e S S H B ia s N o m in a l M e a n = + 1 2 6 ± 6 m m , σ = 2 2 mmmmmmmmm* mmmm = + 9 4 ± 7 mm, σ = 2 6 mmmmmmm-1 mmmmmm mmmmm*mmmmm-1 : mmmmmmm mmm-m mmmm mmm-m mmmmm/mmmmmmmm: mmm mmmmmmmmm mmmmm mmm mmm mmmm mmm


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Harvest SSH Bias During Jason-1 Verification Phase(Tandem Chase Orbit)

Jason-1 — T/P; Median = 100 mm, σ = 29 mm/ ( - ); = –8 , T P ALT B Median mmσ = 32 mm

-1; = 107 , Jason Median mmσ = 32 mm

( )Relative Bias mm

-1 Jason Repeat Cycle


T/P (ALT-B) Retracked Data



Relative Ku-Band Range During Jason-1 Verification Phase:(HORBIT – RKu)JASON — (HORBIT – RKu)TOPEX

Strategy No Mean Median σ

Nominal 34 –3 ± 6 –8 34

LSE 34 +3 ± 6 +4 36

Map 34 –39 ± 9 –56 52

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Nominal: Median = +66/+67 mm , σ = 34/35 mm- : = +72/71 , ALT B LSE Retracking Median mmσ = 51/28 mm- : = +128/127 , ALT B MAP Retracking Median mmσ = 70/67 mm

-1 Jason Repeat Cycle

SSH Bias (ALT–B) for Repeat Cycles 290–365 (RGDR Release)


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 σo).• High scatter for MAP estimates.


Backup Slides


Geographically Correlated ErrorsJason-1 — T/P SSH (Tandem Verification Phase)

Harvest Corsica

BASS STRAIT

110 142 174(mm)

ASC. TRACKS σ = 16 mm

DES. TRACKS σ = 12 mm

110 142 174(mm)

• 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)


Geographically Correlated Errors Remain SSH Bias: Harvest vs. Global Results

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Jason-1 — T/P Relative SSH Bias

Ascending Tracks: Mean = 134 mm, σ = 12 mm = 132 ,Descending Tracks Mean mm σ = 9 mm

( 43)Harvest Ascending Pass

( )Relative SSH Bias mm

( )Latitude deg

23 mm


Calibration of Ionosphere Delay at HarvestUSING DATA FROM JPL GIM SOLUTION

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Ku-Band Zenith Ionosphere Delay

ALT-A Bias (2002.0) = +1.7 ± 7.9 mm, Rate = +0.9 ± 2.3 mm/yr ALT-B Bias (2002.0) = –2.2 ± 0.8 mm, Rate = 0.0 ± 0.5 mm/yrJGDR-A Bias (2002.0) = –5.1 ± 0.8 mm, Rate = +1.2 ± 0.4 mm/yrJGDR-B Bias (2002.0) = –3.0 ± 1.6 mm, Rate = +1.7 ± 0.6 mm/yr

Delay (mm) ( )Delay mm


Jason-1 SSH Stability Estimates

Jason-1 GDR (Ver. A)

+ GPS Orbit

+ GPS Orbit + GPS Wet Path Delay

+ GPS Orbit + Calibrated JMR data

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NomNom fit

Rate = –9.2 mm/yr

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Gps OrbitGps fit

Rate = –6.4 mm/yr

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GPS GPSGPS GPS fit

Rate = 0.0 mm/yr

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GPS JMRGPS JMR fit

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Rate = –1.1 mm/yr


Conditions at Harvest are Typical of Open Ocean

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SWH (m)

January 2001 Day

Harvest H 1/3

: January 2001

Data Courtesy SIO/CDIP Program (Harvest Buoy)


Periodicities in the Platform Height

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Before Application of Thermal/Loading Models After Application of Thermal/Loading Models

Amplitude (mm)

Period (d)

Annual3.5 yr


Geographically Correlated Radial Orbit Error RateGDR Orbit — JPL GPS: Radial Rate for Cycles 1–90

Harvest: Rate = –6.6 mm/yr

Corsica: Rate = –0.5 mm/yr

Bass Strait: Rate = –4.9 mm/yr

–10 100mm/yr

Ascending Tracks Descending Tracks

All Tracks


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


CU Laser Sea Level System


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.


CU Sea Level System


Error Budget: Bias

SOUTHMean = 164.6 mmσ = 10.8 mm

TROPICSMean = 154.1 mmσ = 10.7 mm

NORTHMean = 160.0 mmσ = 12.0 mm

GLOBAL Mean = 159.0 mm σ = 12.1 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

SOUTHMean = 172.5 mmσ = 10.9 mm

TROPICSMean = 152.1 mmσ = 11.4 mm

NORTHMean = 148.1 mmσ = 12.7 mm

GLOBAL Mean = 160.0 mm σ = 15.9 mm

Jason-1 – T/P Sea Surface Height: Ascending Tracks

Formation Flying PhaseJason-1 GDR: Cycles 1–21

T/P MDGR + TMR Drift Correction: Cycles 344–364

mm

monitoring jason-1 and topex/poseidon from a california offshore platform: latest results from the...

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