Summary of issues and conclusions from DMQC-4 Pressure Issues, especially Surface pressure offset, Druck microleak, APEXs that truncate negative pressures Other issues. All delayed-mode groups to be aware of increased possibility of SBE CTDs developing the Druck microleak disease.
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Pressure Issues, especially Surface pressure offset, Druck microleak, APEXs that truncate negative pressures
All delayed-mode groups to be aware of increased possibility of SBE CTDs developing the Druck microleak disease.
Combined Apf-9 data from BSH, UW, and CSIRO, up until 22 August 2009.
Occurrence rate up until Mar 09
Pre-2008 ~ 3%
UW ice floats Jan 2008 18%
(after 14 months)
UW + SIO floats
Kaharoa Oct 2008 28%
(after 5 months)
Both occurrence rate and oil leak rate have increased!
Stephanie Guinehut’s altimetry QC can detect errors that correspond to about 5 cm of dynamic height.
Because of the thermal structure of the ocean, this is equivalent to about 10 dbar pressure error in the tropics, but about 50 dbar at high latitude.
Therefore the altimetry QC will be most useful at latitudes < 30.
For such APEX floats, if the Surface Pressure ‘hovers around zero’ there is no problem.
If Surface Pressure becomes ‘persistently’ zero, but other data are ‘sensible’ the unknown surface pressure offset is negative. The magnitude is unknown but probably < ~ 20 dbar if the other data have no obvious problem. When such a float is identified, DM proposes: (see next page)
For TNPD floats with persistently zero surface pressure
For APEX Apf-5, Apf-7, Apf-8 (all firmwares that truncate negative surface pressure values), when a large portion of the SP time series (nominally 80%) records absolute zero AND T/S does not show anomaly, it means the float may be experiencing undetectable negative pressure error. In those cases:
PRES_ADJUSTED_QC = ‘2’
TEMP_ADJUSTED_QC = ‘2’
PSAL_ADJUSTED_QC = ‘2’
SCIENTIFIC_CALIB_COMMENT = “TNPD: APEX float that truncated negative pressure drift. Other operator comments,……”
For TNPD floats with persistently zero surface pressure
If fhere is an apparent T/S anomaly, it is very likely that there is a pressure problem and the flags should be ‘3’ or ‘4’ depending on severity of the anomaly.
A negative PRES error will lead to a positive PSAL error, and a cold TEMP anomaly whose size depends on vertical TEMP gradient
If the float is telemetering highly erratic data, it is a sign that the microleak problem is about to reach its endpoint. Previous cycles may need to be reviewed.
For TNPD floats with persistently zero surface pressure(continued)
Justin Buck & Mathieu Ouellet to consult their assimilation groups about how they use PRES_ADJUSTED_ERROR and to suggest to DM community what value should be assigned for APEX TNPDs to ensure that these data are treated appropriately by those groups.
For the cases of APEX TNPDs, what to do with
PRES_QC, TEMP_QC, PSAL_QC?
Comment: When the pressure goes really bad, the float will go on the greylist.
Before that time, DM suggests that in real time, PRES_QC, TEMP_QC, PSAL_QC should be ‘2’ in the GDAC files. Should these data be transmitted on the GTS ?
For floats with microleaks
Be aware that if the pressure offset is <~ 10 dbar, the error may be independent of depth, so a simple pressure adjustment is appropriate; but if pressure offset is >~ 10 dbar, the error may vary with both PRES & TEMP
Chair AST will write to SBE and ask them to characterise pressure errors from microleaks for the sensors they have already identified as bad in their laboratory tests
Editing raw flags
11. A suggestion was made that if PSAL is adjusted in delayed-mode, then PSAL_QC should be ‘3’ because ‘These data should not be used without scientific correction’. Agreement was not reached on whether to instruct all DM operators to adopt this. Some DACs/DM operators may choose to do this if they wish.
12. The question was posed: ‘Should we remove D files that haven’t been reprocessed for surface pressure offset, and restore them when the DM operator has completed the task ?’
The answer was:
‘No. We cannot afford to lose that many D files; DACs should fix them as a high priority’. If it is critical to users to know whether surface pressure has been adjusted, they must read the SCIENTIFIC_CALIBRATION_COMMENT.’
(reflects the way DM community has viewed data for some time)
REAL-TIME versus DELAYED-MODE
→ 2 stages of data quality control
RAW versus ADJUSTED
→ 2 types of data
Change definitions of PARAM and PARAM_QC in User’s Manual and QC Manual:
▪ PARAM contains the raw values telemetered from the floats. PARAM = PRES, TEMP, CNDC, PSAL.
(DOXY will have its own definition.)
▪ PARAM_QC contains qc flags that give information about the values in PARAM. Values in PARAM_QC are set initially in ‘R’ and ‘A’ modes by the automatic real-time tests. They are later modified in ‘D’ mode at levels where the qc flags are set incorrectly by the real-time procedures, and where erroneous data are not detected by the real-time procedures.
Thermodynamic Equation Of Seawater - 2010
www.teos-10.org, (top hit for “teos-10” in google)
TEOS-10: Approved by IOC June 2009 for use from Jan 2010 onwards
DMQC-4 reviewed the impact of TEOS-10 on the DM process, which will be small
TEOS-10 libraries available in Matlab & FORTRAN; c will come in due course
Note that the salinity argument for the TEOS-10 algorithms is Absolute Salinity
SA =~ 1.004715 *PSAL + regional composition anomaly of magnitude <~ 0.02.
function SA = gsw_ASal(PSAL,PRES,LON,LAT)
function result = gsw_pden(SA,t,p,pr)
function result = gsw_ptmp(SA,t,p,pr)
Extends algorithms to larger ranges, which were not defined for PSAL & EOS80
( 0 < S < 120; T < 80)
Units of SA are g/kg