# Presentation: 196453

## Metadata Limitations and the effect on XBT depth adjustment

**A. Gronell and R. Cowley**
**CSIRO Marine and Atmospheric Research**
**  **

## Why we’re interested:

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**Notes:**
Our Quota project is an on-going quality assessment of all the upper ocean temperature data we can assemble.  Data for this project comes from the  World Ocean dataset, GTSPP, NODC, Far Seas fisheries, Noumea and others.  

As well as finding and removing bad data from the archives, using statistical screening with manual QC of profiles that fail the screening, we aim to provide the highest quality dataset possible. This requires that we address the question of fall rates of the XBTs in the archive.  Our focus at this point is not to correct for the bias we’re discussing here, but rather to get all the XBT data into the same state, using the Hanawa fall rate coefficients, so that anyone who uses the data knows that all profiles are directly comparable.  Down the track, if a method is proposed and accepted to correct for the bias through time, we will probably incorporate it into the Quota archive as well.

## 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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**Notes:**
No rounding or truncation errors any more.

## 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

**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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**Notes:**
This is why we split the previous slide into pre and opst 1975. MBTs were tailing off in the early 1970’s and suddenly jumped indicating they might be misidentified XBTs

## 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.

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