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Sections below: Float counts | Meta Files | Tech files | Plots & listings | Surface Pressure | TNPD Argo file format and Surface Pressure correction compliance AuditSpecific comments on this audit, based on GDAC at 6 August 2011Unresolved interpretation of surface pressure parameter names (with SOLO and PROVOR floats)The Table listing tech file Surface Pressure Parameter Names can be found under www.argodatamgt.org/Documentation > Argo data formats > Argo technical files . It associates each name with the method of surface pressure correction to be applied to each float. It is the basis for this audit. PRES_SurfaceOffsetNotTruncated_dBAR is listed as: not auto-correcting
Description: Surface pressure recorded just before the previous
descent - Note: this is a cumulative offset, This IS NOT used
to correct pressure on board
Use: In real-time, subtract the cumulative offset from the reported
pressures of the present profile. In DMQC, apply this value to the
reported pressures of the PREVIOUS profile.
Many of the SOLO and PROVOR floats using this parameter name are not being
corrected as defined above. Instead, no correction
at all is applied for many or all profiles. An audit would normally show
those floats as wrongly corrected. However for this audit both the
"correct" and the alternative "no correction" treatments have been allowed, and
instances of "no correction" have been highlighted in the plots and the
Pressure Correction Summary listings. Lime green is used to highlight this
condition in the plots (eg 1900035.gif ) and orange (the same colour as this text) is used in the
9th column of the summary listings, eg:
There are perhaps four ways to resolve this:
(SOLO floats with parameter name PRES_SurfaceOffsetBeforeReset_dBAR also may have one of two treatments, and so may be highlighted in the same way. However, these alternative treatments are acknowledged in the Table so the audit recognises them as correct.) Unknown Parameter NamesThere are still some parameter names in use which are not listed in the official Table (these are highlighted in pink in the "Surface Pressure Offset parameter name" table below.) This means that we cannot know how those floats should be pressure corrected. Either the Table should be updated to include these names, or the tech files should be rebuilt using the correct names from the official Table. TNPDIdentification of TNPD floats is still improving, with all but one DAC now applying the agreed protocols. Several DACs are using SCIENTIFIC_CALIB_COMMENT strings which do not exactly match the agreed string (see "Imperfect COMMENTS present" row of TNPD Report .) Note that the difference is only in the use of: TNPD: APEX float that truncated negative surface pressure drift or TNPD: APEX float with truncated negative pressure drift instead of TNPD: APEX float that truncated negative pressure drifthowever it was agreed that exactly this last string would be used. Pressure correction summaryThere is general progress by most DACs. Some discrepancies in CSIRO and INCOIS floats were found to arise from my own DM-QC coding error (egg on my face!). The improvement in CORIOLIS pressure correction statistics is exaggerated by the temporary allowance for alternate treatment of some PROVOR floats, as talked about above.
> NEW summary table
Argo Technical and Meta file compliance AuditThis page is automatically created by code which scans all files in the Argo USGODAE GDAC. Previous audits can be accessed via the CSIRO DMQC page This analysis was based on GDAC as at 06-Aug-2011 Float counts in DACs
Meta files
tech files
Plots and listings analysing the Surface Pressure Offset
correction for
all floats for each DAC are accessed through the
Plots Index Tables. Separate tables link to all floats, or only floats
with apparent SP correction anomalies, or only floats with apparent TNPD.
Note: The following analyses were based on assumptions about
behaviour of different types of floats, where "type" was here primarily
defined by the Surface Pressure Offset parameter name. Some of these
assumptions will be wrong, and some types are not analysed at all because I
am unsure of their behaviour. It is probably necessary to also take basic float
model (eg Apex or SOLO) into account to fully determine the pressure correction
treatment required for a float, but it would be better if this could be fully
determined by just the parameter name. My assumptions are recorded in this
table.
Surface Pressure OffsetWe have attempted to test for correct Surface Pressure (SP) correction of profile pressure. The difference between PRES and PRES_ADJUSTED is the DAC-applied pressure correction (assuming PRES is the raw P as reported by the float.) Correct application of this test depends on being able to deduce the correct float type and P adjustment from the meta and tech files. However this is not always possible due to missing or non-standard entries in these files. Our computed pressure correction is p_calc = PRES - (SP - adjustment)where adjustment is the known SP adjustment for a given float type (usually 5dbar). For Apex floats the SP reported with a profile actually relates to the previous profile, because it was recorded just as the float begins to descend. RT profile pressure can only be adjusted with the SP reported with the same profile, but in DM profiles the correct SP is used (ie for profile N, p_calc(N) = PRES(N) - (SP(N+1) - adjustment)So, in the provided plots , for floats which do not auto-correct, the "Calculated Correction" (CC) is For DM profiles: CC = SP(N+1) - adjustment
For RT profiles: CC = SP(N) - adjustment
For this reason, CC will differ from Raw Surface Pressure by the "offset", and
will be displaced by one profile for DM profiles. The "DAC adjustment" should
however agree with the CC.
Interpretting the plots: For complete agreement in pressure correction, the "DAC Adjustment" (blue squares), should agree with the CC (red stars). Missing "DAC Adjustment" symbols can occur where there is no PRES_ADJUSTED profile (eg if QC=4). Missing CC symbols can occur where the DAC has provided an SP estimate (possibly by interpolation) but the automated process has not [due to different processing or because the tech files are not quite up-to-date.] Disagreement is likewise visible where "MPP minus CC" (cyan diamond) does not overlay "Min Corrected Pressure" (magenta square). The latter quantity is just the near-surface PRES_ADJUSTED value. Note that the raw SP symbols (blue diamond) are shown exactly as found in the tech files. That is, their x-coordinate is the cycle number corresponding to that value in the tech files. A light gray background is used where disagreement is between 0.1 and 1.0 dbar. This occurs frequently due to DAC smoothing of the SP series, or for other reasons. A dark gray background indicates disagreement greater than 1.0 dbar. Some of these cases are due to deficiencies in our automatic procedures, but some others appear to be related to processing faults at the DACs. An olive green background behind the CC value indicates an alternative correction method (such as allowed for SOLO floats) gives better agreement with the DAC value than the primary method. The CC value shown is then as derived by the alternative method. For example, SOLO floats are auto-correcting, so the primary method is "no correction". However, a secondary method - the normal SP(n+1) correction - may be applied in DM if there is evidence of strong drift. A very pale green background indicates that the DAC has explained how their adjustment is correct, or pointed out that the CSIRO audit software has made a mistake. Any disagreement in these profile is ignored when collating statistics.
See the table which summarizes the results of this pressure correction audit for all DACs. Lists: for each DAC a text file (accessable through the Plots Index Tables) lists the result of checking the surface pressure correction for every float. The floats are grouped by PI. The lists give the number of DM profiles, total number of profiles, assumed surface pressure offset, and counts of profiles which agree exactly or disagree with my automated correction. Please note that in many cases the disagreement is because your DAC correction is a better choice than my automated one. Format example: 5900033 DM 264/295 SPoffs=5 Diffs(dbar) =0[271] <1 [0] >1 [ 1 *] Of 295 profiles for this float, 264 have been DM processed. 271 profiles exactly
agree with my automated correction, 0 disagree by a small amount, but 1
disagrees by more than 1 dbar.
TNPDTruncated Negative Drifting Pressure (TNPD) is a term used to describe Apex floats which truncate negative surface pressure values (all firmware prior to APF9) and the pressure sensor develops a strong negative drift. The usual cause of strong negative drift in these sensors is the "microleak" fault associated with Druck sensors. The pressure in profiles affected by TNPD cannot be corrected for surface pressure offset. The first step in detecting TNPD is to determine if a float is of the type where such an fault might occur. We have attempted to do this using the tech and meta files alone, but this is not always possible. The next step is to find where the reported SP (corrected for 5dbar adjustment if necessary) has "flat spots" on zero, indicating that negative values are being truncated. Previously a float with 80% SP=0 was declared to be TNPD. We now say that any susceptible float is in a TNPD state after the last believable positive SP value. This is because the strong negative drift condition is typically monotonic, so if such a condition has commenced then typical variability will not give rise to small positive SP values. The main difficulty of this approach [assuming the basic assumptions are correct] is determining when isolated positive values are natural perturbations about a small negative value, or when they are just sensor error spikes. In the present analysis I have used (for the first time) the crude test that a positive value > 1dbar which has 2 zero values immediately either side of it, is a spike that can be ignored. [This differs to the standard despiking process used to prepare the SP series for pressure correction because here we just want a simple way of assessing where an SP series is devoid of true +ve values.] Obviously this is very imperfect - there is no substitute for skilled DM analysis, and in very many cases the DAC will be right and our algorithm will be wrong. Another deficiency of our algorithm is that is [apparently] extremely unlikely that microleaking will start after years of correct operation. For example, if SP is 0 for the last 5 of 200 profiles then the algorithm says TNPD commenced at profile 196. The time of onset of TNPD is examined in this set of TNPD plots. That page also includes plots which examining whether, for different sensor types, a large negative drift can be followed by recovery to plausible positive SP values. "Start of TNPD" in the surface pressure plots provided indicates where TNPD appears to commences, according to the above algorithm, if that is at least 6 months before the last DM profile. If the condition is met with less than 6 months of subsequent DM profiles, then 'Potential TNPD' is displayed. Where some of the float series has been DM processed, extra information is provided for the DM profiles in an extra frame at the top of the figure. See the table which summarizes the results of this TNPD treatment audit for all DACs. Lists: for each DAC two text files (accessable through the
Plots Index Tables) list the result
of checking for TNPD. The floats are grouped by PI.
The "short" list gives the cycle number ("pn") where TNPD appears to start,
and counts of profiles which appear to require the TNPD comment string and do not
have it ("missed"),
or do have the comment string ("good"), or have a comment string which is not
precisely the standard string ("imperfect"). The list also notes where we have
NOT detected TNPD but have found the TNPD comment string.
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