Metadata Limitations and the effect on XBT depth adjustment
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Transcript of Metadata Limitations and the effect on XBT depth adjustment
Metadata Limitations and the effect on XBT depth adjustment
A. Gronell and R. CowleyCSIRO Marine and Atmospheric Research
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Depth correction:
We need entire database to same vertical scale
• We do this by converting all t-7, deep blue, t-6 and t-4 profiles to conform to the Hanawa ‘85 equations
• High or full vert resolution depths are recalculated and replaced.
• Low vert resolution data depths are multiplied by 1.0336
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Depth correction procedures:
• High vertical resolution profiles with ‘known’ probe type : ‘fixes’ profiles with truncated or rounded depths.
• Replace depths with calculated depths. All depths now to .01 resolution
• Low resolution profiles that either need correction (DPC$01) or are of unknown probe type and fit the criteria for correction:
• Multiply depths by 1.0336
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• Inadequate Metadata is currently the biggest hurdle
• GTSPP best copy datasets for IO were downloaded and run through Depth correction software
• Anything that was not straight-forward was revisited
• 37678 profiles were screened
Issues affecting depth correction decisions
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Metadata issues – con.
• Profiles from GTSPP best copy – 37378 profiles
No probe type info 18303 Action depends on date and max depth
PEQ$ missing but determined from elsewhere and added
11442 Action depends on probe type determined
Missing DPC$ field 156 Action depends on date and max depth
• Profiles with DPC$03 or no DPC$ – 18933 profiles
<200m OR >1000m OR post 1996 3960 Do not change depths
>200m AND <1000m AND pre 1996 14973 Change depths
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Metadata problems found in GTSPP best copy dataset
• CTDs that were identified as XBTs – this is a problem if the DPC$ field is 03 and they fit our other criteria
• T10 profiles that go to 1500m (actually t-5 probes)
• MBTs misidentified (probably XBTs) – max depth for MBTs is ~250m
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MBTs that go deeper than 300m
Red profiles are post 1975
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MBT distribution in the Indian Ocean through time
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Other issues
• Number of depths wrong – more or fewer in the parameter field
• Additional or missing depths – in full resolution profiles, depths duplicated or missing
• Deep_depth field value different from the actual deepest depth
• Single point profiles
• Profiles with exactly .6m resolution (depths assigned and not calculated?) – results in error of ~30m at 800m
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Conclusions:
• Codes are confusing – there are too many places to find probe type information
• PEQ$• PRT$• FRE$• PTY$• PFR$
• We should be able to reconcile all these into a sensible PEQ$, even if it’s unknown.
• DPC$ need clarification – • 03 = not enough information, do not correct – but we know
most of these should be corrected.• 02 = known probe type, no correction – what does this
mean? No correction done or no correction necessary?
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Conclusions (con):
• To effectively calculate the corrections needed to fix the fall rate bias of XBTs, we need the best quality baseline data – all using the same base-line fall rate. We therefore need smart methods to get all profiles to the Hanawa equation.
• We can only do this if we have adequate metadata – otherwise, we’re just making educated guesses.