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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 AuditComments on Argo Audit using GDAC at 18-Dec-2010Multiple SP parameters per profileThis is the first audit run to take account of multiple Surface Pressure parameter names per cycle in the tech files. This takes two forms:
A related anomaly is where the SP parameter name is not the same for all cycles of a float. A number of these were detected but they may all have been where no SP was reported for the first cycle only, which is benign and will be ignored in future audits. The above conditions are reported in the individual plot titles, and in the per-float listings (multiple SP Param name codes are shown, or that field is red if the name is not present and identical for every cycle. ) Counts of these conditions have been added near the bottom of the "Surface Pressure Offset parameter name" table. Changed order of gathering statsSome statistics have changed because of reordering of selection and counting in the code, and inclusion/exclusion of certain degenerate cases (eg floats without any profiles, or of unknown type, or lacking any SP values.) SP Parameter Name useWhere possible the audit code adheres to the Treatment vs SP Parameter Name table recently published ( http://www.argodatamgt.org/content/download/5478/39874/file/Surface%20PressureCorrectionTable_Final.xls ). This has changed the interpretation of some floats - especially that "BeforeReset", which are auto-correcting, should benefit from post-correction. This interpretation is still debated and clearly does not agree with the use by some DACs. Many floats are probably pressure-corrected correctly, but are reported as a discrepancy only because the provided Surface Pressure Parameter name implies a different treatment to that applied by the DAC. Pressure Correction changes within a profileMost of these cases identified previously were due to a correct adjustment of the deepest pressure value in SOLO floats. This condition has now been allowed so there are now few reported cases. SP spike filteringSP spike filtering that is a slightly enhanced version of the recommended RT filter is now used. Because this is non-standard it will give rise to some differences, but then there will always be differences due to DM manual intervention. [Do you want details of the spike filter?] Argo Technical and Meta file compliance AuditThis page is automatically created by code which scans all files in the Argo USGODAE GDAC. Previous versions can be accessed via the CSIRO DMQC page This analysis was based on GDAC as at 18-Dec-2010 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 , the "Calculated Surface Pressure" (CSP) is For DM profiles: CSP = SP(N+1) - adjustment
For RT profiles: CSP = SP(N) - adjustment
For this reason, CSP 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 CSP.
Interpretting the plots: For complete agreement in pressure correction, the "DAC Adjustment" (blue squares), should agree with the CSP (red stars). Missing "DAC Adjustment" symbols can occur where there is no PRES_ADJUSTED profile (eg if QC=4). Missing CSP 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 CSP" (cyan diamond) does not overlay "Min Adjusted Pressure" (magenta square). The latter quantity is just the near-surface PRES_ADJUSTED value. 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. 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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