Metadata Limitations and the effect on XBT depth adjustment

1
Metadata Limitations and the effect on XBT depth
adjustment

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

2
Why were interested
3
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

4
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 (DPC01) or are of unknown probe type
  and fit the criteria for correction
• Multiply depths by 1.0336

5
Issues affecting depth correction decisions

• 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

6
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 DPC03 or no DPC 18933 profiles

lt200m OR gt1000m OR post 1996 3960 Do not change depths
gt200m AND lt1000m AND pre 1996 14973 Change depths
7
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

8
MBTs that go deeper than 300m
Red profiles are post 1975
9
MBT distribution in the Indian Ocean through time
10
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

11
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 its 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?

12
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, were just making educated guesses.