Altimetry for coastal oceanography in Australia -an assessment of PISTACH

David Griffin, Madeleine Cahill,

Jim Mansbridge, Neil White

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Much of Australia has shelf-edge jets

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Australian Baseline Array of quality tidegauges

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Since 2004: altimetry + tidegauge -> shelf current

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First attempt at including PISTACH on-shelf FASL in a Jason-1, -2, Envisat, Tidegauges OI map

• FASL=Filtered (ie no tides) Adjusted (ie bottom-pressure equivalent) Sea Level. (anomaly understood)

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One-month animation of FASL maps

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Doesn’t look right. What are we doing wrong?

• SL = Orbit – range – iono – dry – wet – ssb – mss – solid Earth & pole tides. (correct either alt or TG for loading tide)

• FSL = SL – geocentric ocean tides (alt), Low-pass filter TG• FASL = FSL – IB(isostatic) – HF corrections (MOG2d)• Options tried:• Orbit: IGDR MOE, GPS OGDR• Range: IGDR, OCE3, RED3• Iono: GIM (J2 C band has problems)• Dry: model• Wet: radiometer, composite, decontaminated• SSB: ssb_ku• MSS: mss1(CLS01V1), mss3(DNSC08)• Ocean tide: tide1 (Got 00), tide2(FES04), tide3(GOT 4.7)

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Study period: cycles 1-43 (July 2008 – Sep 2009)

• IGDR, PISTACH v0, v3, v4• v0: MOE, mss3(DNSC08), red3, decont_wet, tide3(GOT4.7)• v3: oce3• v4: composite wet• compute correlation, regression, mean and std dev of

difference pointwise along track (1Hz averages) with • Esperance (70km shelf) and Thevenard (200km shelf)• for FASL, FSL, SL

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Esperance FASL corr with IGDR

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Esperance FASL corr with PISTACH v0. - much more data. (but why tracks different?)

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Esperance FASL corr with PISTACH v3 (oce3).- less correlation than red3

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Esperance FASL regress with PISTACH v0.- implausible(?) gain pattern with red3, suspect noise

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Esperance FASL bias with PISTACH v0.- small along track gradient, but big inter-track difference

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Esperance FASL cf PISTACH v0 (3 closest good 1Hz).Much within-day change. Peaks unsampled. OI no hope

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Esperance FSL cf PISTACH v0 (3 closest good 1Hz).- IB relatively small

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Esperance SL cf PISTACH v0 (3 closest good 1Hz).errors are the same with IB and tides not removed

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Esperance SL cf PISTACH v0 (pass 64)- hard to complain with r=0.96

• r=0.96, G=0.84, std. dev 72mm, bias -111mm, 15km distance

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Esperance FASL cf PISTACH v0 (pass 64). r=0.67. sd 77mm. Residual tide + other HF?

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Esperance FASL cf PISTACH v0 (pass 227).- 3d offset: uncorrelated signal and errors cf pass 64

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Reminder: problems near Thevenardpass 114, cycle 33:

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Thevenard SL corr with PISTACH v0.at coast: 114, 201, 23

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Thevenard SL cf PISTACH v0 (pass 114)some big (400mm) errors, but 29 May OK:

• r=0.88 G=0.65, sd 190mm, 28 km from coast

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Thevenard FASL cf PISTACH v0 (pass 114). errors up to 400mm, eg 29 May

• r=0.56, G=0.54, sd=130mm. 9.8km from coast

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Thevenard SL cf PISTACH v0- note 3 high tides daily 29 May – 5 June

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Thevenard FASL cf PISTACH v0.400mm error on 29 May ruined OI map

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Burnie (pass 225)

• 500mm+ outliers• otherwise good

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Burnie J1 CalVal.40.5mm std dev using GDR-C

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Conclusions

• PISTACH data has much to offer compared with standard products. But please: more documentation of data products!

• These three example tidegauges highlight unresolved site-specific issues

• Esperance: SL has 70mm std dev noise. ~OK• Big discrepancies at Thevenard not yet explained.• For FASL, some of the error may be un-modelled M3 tide (cf R

Ray)• But SL errors are also large (up to 400mm,130mm sd) • must also remember: 10-day sampling grossly inadequate to

capture all shelf variability• even daily-averages are inadequate, need 12h.• To do: 1) better tide model, 2) check SSB

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Thankyou

• Pierre Thibaut, Franck Mercier, Claire Dufau

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Esperance FASL regress with IGDR.- question did not arise with IGDR

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Esperance FASL regress with PISTACH v3 (OCE3).- severe coastal trapping