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

Shailen DesaiShannon Brown

Bruce HainesWenwen Lu

Victor ZlotnickiJet Propulsion Laboratory, California Institute of Technology

Ocean Surface Topography Science Working Team Meeting, March 14, 2007

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

SD/SB/BH/WL/VZ - 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

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

SD/SB/BH/WL/VZ - 3

Validation of TMRMGDRB and Replacement Product

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TMR(MGDRB)-GPSTMR(MGDRB)-SSMITMR(MGDRB)-TMI

Topex Repeat Cycle

TMR from MGDRB

• TMR from MGDRB• 0.8 mm/yr drift from cycle

30-240• ~5mm peak-to-peak

dependence on satellite attitude regime (yaw state).

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TMR (RP) - GPSTMR (RP) - SSMITMR (RP) - TMI

Topex Repeat Cycle

TMR from Replacement Product (RP)

• 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.

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

SD/SB/BH/WL/VZ - 4

Daily Averages of TMR vs. SSMI and TMI

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TMR(MGDRB)-SSMITMR(MGDRB)-TMI

Days Since Jan 1, 1992

TMR from MGDRB

• TMR from MGDRB• Systematic yaw state errors

distinct in daily averages.

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TMR (Recal.) - SSMITMR (Recal.) - TMI

Days Since Jan 1, 1992

TMR from Replacement Product

• TMR from Replacement Product

• Yaw state errors removed.

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

SD/SB/BH/WL/VZ - 5

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.

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JMR (GDRB) - GPSJMR (GDRB) - SSMIJMR (GDRB) - TMIJMR (GDRB) - ECMWF

Jason Repeat Cycle

JMR from GDRB

• 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.

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JMR (Recal.) - GPSJMR (Recal.) - SSMIJMR (Recal.) - TMIJMR (Recal.) - ECMWF

Jason Repeat Cycle

JMR from Recalibration

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

SD/SB/BH/WL/VZ - 6

Scatter of JMR versus ECMWFJMR 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.

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

SD/SB/BH/WL/VZ - 7

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.

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TMR(MGDRB)-JMR(GDRB)TMR(RP)-JMR(GDRB)TMR(RP)-JMR(Recal.)

Topex Repeat Cycle

Cycle Averages

• Temporal variation of standard deviations of recalibrated TMR and JMR very consistent at 3 mm.

– Random noise ~ 2mm.

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TMR(MGDRB)-JMR(GDRB)TMR(RP)-JMR(GDRB)TMR(RP)-JMR(Recal.)

Topex Repeat Cycle

Cycle Standard Deviations

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

SD/SB/BH/WL/VZ - 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.

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

SD/SB/BH/WL/VZ - 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.

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TMR(MGDRB)-JMR(GDRB)TMR(RP)-JMR(GDRB)TMR(RP)-JMR(Recal.)

Distance from Land (km)

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

SD/SB/BH/WL/VZ - 10

Average of Differences w.r.t. Independent Measurements

TMR (RP) JMR (GDRB) JMR (Recal.)

SSMITMIGlobal GPSContin. GPSIsland GPS

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TMR (MGDRB)

Average of Wet Path Delay Differences (mm)

• 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.

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

SD/SB/BH/WL/VZ - 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.

BACKUP SLIDES

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

SD/SB/BH/WL/VZ - 13

Senatosa

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Distance from Land (km)

TMR-JMR Wet Path Delay (mm)

Time to Senatosa (sec)

TMR wetter orJMR drier betweenland masses.

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

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Scatter of TMR(RP) vs JMR

March 14, 2007 Ocean Surface Topography Science Working Team MeetingCal/Val Splinter Session

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Mean Offsets w.r.t. Independent Measurements

Radiometer SSMI TMI Global GPS

IslandGPS

Continental GPS

TMR(MGDRB) 2.4 4.3 -5.8 -0.4 -8.2

TMR (RP) 6.0 7.7 -2.4 1.8 -4.4

JMR(GDRB) 3.2 2.6 1.7 -1.8 1.1

JMR(Recal.) 5.6 6.7 4.2 1.0 3.3

• 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.