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Argo Quality Control Manual Version 2.1
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1. T S relation will look acceptable but at depth it will look as if the float is sampling an anomalous water mass relative to nearby floats Delayed mode analysts should try to re scale pressure measurements e g PRES PRES X to see whether the T S curve can be recovered Air bubbles in the pressure transducer can also cause erroneous pressure measurements that are visible as anomalous T S curves 9 Thermal inertia lag Salinity reported immediately after a float has crossed a strong thermal gradient can be in error as a result of conductivity cell thermal mass This error arises because of heat exchange between the conductivity cell and the water within it A float that transits from cold to warm water can result in fresh error and from warm to cold in salty error These errors can exceed 0 01 PSS 78 for strong thermal gradients and sometimes result in unstable fresh spikes at the base of the mixed layer Argo data management quality control manual 30 11 2004
2. assumes a sampling that adequately reproduces the temperature and salinity changes with depth The algorithm is used on both the temperature and salinity profiles Test value V2 V3 V1 21 1 V3 V1 21 where V2 is the measurement being tested as a spike and V1 and V3 are the values above and below Temperature The V2 value is flagged when e the test value exceeds 6 0 degree C for pressures less than 500 db or e the test value exceeds 2 0 degree C for pressures greater than or equal to 500 db Salinity The V2 value is flagged when e the test value exceeds 0 9 PSU for pressures less than 500 db or e the test value exceeds 0 3 PSU for pressures greater than or equal to 500 db Action Values that fail the spike test should be flagged as bad data and are removed from the TESAC distributed on the GTS If temperature and salinity values at the same depth both fail they should be flagged as bad data and the values for depth temperature and salinity should be removed from the TESAC being distributed on the GTS 10 Top and bottom spike test obsolete 11 Gradient test This test is failed when the difference between vertically adjacent measurements is too steep The test does not consider the differences in depth but assumes a sampling that adequately reproduces the temperature and salinity changes with depth The algorithm is used on both the temperature and salinity profiles Test value V2 V3 V1 2 where V2 is the
3. gt _ADJUSTED_QC becomes available Lastly the name of the single profile Argo netcdf file is changed from R nc to D nc Argo data management quality control manual 30 11 2004 a 3 3 9 Timeframe for availability of delayed mode salinity data The statistical methods used in the Argo delayed mode process for checking sensor drifts and offsets in salinity require the accumulation of a time series for reliable evaluation of the sensor trend Timeframe for availability of delayed mode salinity data is therefore dependent on the sensor trend Some floats need a longer time series than others for stable calibration Thus delayed mode salinity data for the most recent profile may not be available until sufficient subsequent profiles have been accumulated The default length of time series for evaluating sensor drift is 12 months 6 months before and 6 months after the profile This means that in general the timeframe of availability of drift adjusted delayed mode salinity data is 6 months after a profile is sampled Users should also be aware that changes may be made to delayed mode files at any time by DACs and delayed mode operators For example delayed mode files may be revised when new CTD or float data become available after the original delayed mode assessment and adjustment The date of latest adjustment of a parameter can be found in CALIBRATION_DATE Anytime an Argo file is updated for any reason the DATE_UPDATE variable will reflec
4. measurement being tested as a spike and V1 and V3 are the values above and below Temperature The V2 value is flagged when e the test value exceeds 9 0 degree C for pressures less than 500 db or e the test value exceeds 3 0 degree C for pressures greater than or equal to 500 db Argo data management quality control manual 30 11 2004 9 Salinity the V2 value is flagged when e the test value exceeds 1 5 PSU for pressures less than 500 db or e the test value exceeds 0 5 PSU for pressures greater than or equal to 500 db Action Values that fail the test i e value V2 should be flagged as bad data and are removed from the TESAC distributed on the GTS If temperature and salinity values at the same depth both fail both should be flagged as bad data and then values for depth temperature and salinity should be removed from the TESAC being distributed on the GTS 12 Digit rollover test Only so many bits are allowed to store temperature and salinity values in a profiling float This range is not always large enough to accommodate conditions that are encountered in the ocean When the range is exceeded stored values rollover to the lower end of the range This rollover should be detected and compensated for when profiles are constructed from the data stream from the float This test is used to be sure the rollover was properly detected e Temperature difference between adjacent depths gt 10 degrees C e Salinity difference between adja
5. quality control e The first level is the real time system that performs a set of agreed checks on all float measurements Real time data with assigned quality flags are available to users within the 24 48 hrs timeframe e The second level of quality control is the delayed mode system e The third level of quality control is regional scientific analyses of all float data with other available data The procedures for regional analyses are still to be determined This document contains the description of the Argo realtime and delayed mode procedures Argo data management quality control manual 30 11 2004 ST 2 Real time quality controls 2 1 Argo Real time Quality Control Test Procedures on vertical profiles 2 1 1 Introduction Because of the requirement for delivering data to users within 24 hours of the float reaching the surface the quality control procedures on the real time data are limited and automatic The test limits are briefly described here More detail on the tests can be found in IOC Manuals and Guides 22 or at http www meds sdmm dfo mpo gc ca ALPHAPRO gtspp qemans MG22 guide22_e htm Note that some of the test limits used here and the resulting flags are different from what is described in IOC Manuals and Guides 22 If data from a float fail these tests those data will not be distributed on the GTS However all of the data including those having failed the tests should be converted to the appropriate netCD
6. tests passed These data are not to be used without scientific correction A flag 3 Probably bad data may be assigned by an operator during An adjustment has been that are potentially jadditional visual QC for bad data that may be applied but the value may 3 correctable corrected in delayed mode still be bad Data have failed one or more of the real time QC tests excluding Test 16 A flag 4 may be assigned by an operator during additional visual 4 Bad data a for bad data that are uncorrectable sao data Not adjustable S jist charged value changed _Walue charged 6 Notused used e used 7 Not used Notus Noted o O 8 interpolated value _ interpolated value interpolated value 9 Missing value Argo data management quality control manual 30 11 2004 OT TY 4 2 Common instrument errors and failure modes This section describes some common instrument errors and failure modes that will cause error in float measurements 1 TBTO leakage TBTO tributyltinoxide is a wide spectrum poison that is used to protect conductivity cells from biofouling However accidental leakage of TBTO onto the conductivity cell can occur This will result in fresh salinity offsets in float series that usually gets washed off Delayed mode analysts should pay special attention to the shape of the salinity profiles at the beginning of the float series if TBTO leakage is suspected 2 Pollution events Any pollution on the c
7. the 2 average values is more than 0 5 psu then all measurements for this parameter are flagged as probably bad data flag 3 The same test is applied for temperature if the difference between the 2 average values is more than 1 degree C then all measurements for this parameter are flagged as probably bad data flag 3 17 Visual QC Subjective visual inspection of float values by an operator To avoid delays this test is not mandatory before real time distribution Argo data management quality control manual 30 11 2004 18 Frozen profile test This test can detect a float that reproduces the same profile with very small deviations over and over again Typically the differences between 2 profiles are of the order of 0 001 for salinity and of the order of 0 01 for temperature A Derive temperature and salinity profiles by averaging the original profiles to get mean values for each profile in SOdbar slabs Tprof T_previous_prof and Sprof S_previous_prof This is necessary because the floats do not sample at the same level for each profile B Substract the two resulting profiles for temperature and salinity to get absolute difference profiles e deltaT abs Tprof T_previous_prof e deltaS abs Sprof S_previous_prof C Derive the maximum minimum and mean of the absolute differences for temperature and salinity e mean deltaT max deltaT min deltaT e mean deltaS max deltaS min deltaS D To
8. the same float as well as in relation to nearby floats and historical data The assessment should aim to identify a erroneous data points that cannot be detected by the real time qc tests and b vertical profiles that have the wrong shape Bad data points identified by visual inspection from delayed mode analysts are recorded with PRES _ADJUSTED_QC 4 For these bad data points TEMP_ADJUSTED_QC and PSAL_ADJUSTED_QC should also be set to 4 Please note that whenever PARAM_ADJUSTED_QC 4 e PARAM_ ADJUSTED FillValue e PARAM_ADJUSTED_ERROR FillValue Some float groups that have extra information on surface pressure can perform delayed mode adjustments for PRES by comparing measured surface pressure and 0 0 dbar The results are recorded in PRES ADJUSTED PRES ADJUSTED_ERROR and PRES_ADJUSTED_QC Please note that there is no need to recompute PSAL when PRES is adjusted in delayed mode Any salinity offset that may result from PRES adjustments can be reflected in PSAL_ADJUSTED For APEX floats use next cycle SURFACE PRESSURE to adjust PRES if there is evidence that the values reported in SURFACE PRESSURE represent significant sensor related drift or offset PRES_ADJUSTED PRES_ADJUSTED_ERROR PRES _ADJUSTED_QC should be filled even when no adjustment is made In these cases PRES_ADJUSTED_ERROR can be the manufacturer s calibration uncertainty or uncertainty provided by the PI Please use the CALIB se
9. 0N 30E 10N 40E and the Mediterranean Sea by the region 30N 6W 30N 40E 40N 35E 42N 20E 50N 15E 40N 5E 30N 6W Action Individual values that fail these ranges should be flagged as bad data and removed from the TESAC being distributed on the GTS If both temperature and salinity values at the same depth both fail then values for depth temperature and salinity should be removed from the TESAC being distributed on the GTS Red Sea e Temperature in range 21 7 to 40 0 e Salinity in range 0 0 to 41 0 Mediterranean Sea e Temperature in range 10 0 to 40 e Salinity in range 0 0 to 40 0 8 Pressure increasing test This test requires that the profile has pressures that are monotonically increasing assuming the pressures are ordered from smallest to largest Argo data management quality control manual 30 11 2004 OT Action If there is a region of constant pressure all but the first of a consecutive set of constant pressures should be flagged as bad data If there is a region where pressure reverses all of the pressures in the reversed part of the profile should be flagged as bad data All pressures flagged as bad data and all of the associated temperatures and salinities are removed from the TESAC distributed on the GTS 9 Spike test Difference between sequential measurements where one measurement is quite different than adjacent ones is a spike in both size and gradient The test does not consider the differences in depth but
10. Argo data management November 30th 2005 ar um 04 01 ed Q z Q O G G f ge oer G oO 2 O fm G Argo quality control manual Version 2 1 part of the integrated global observation strategy F Table of contents HISTORY 3 AUTHORS 3 1 INTRODUCTION 4 2 REAL TIME QUALITY CONTROLS 5 2 1 ARGO REAL TIME QUALITY CONTROL TEST PROCEDURES ON VERTICAL PROFILES 5 2 1 1 INTRODUCTION 5 2 1 2 QUALITY CONTROL TESTS 6 2 1 3 TESTS APPLICATION ORDER 12 2 2 ARGO REAL TIME QUALITY CONTROL TEST PROCEDURES ON TRAJECTORIES 13 2 3 ARGO REAL TIME SALINITY ADJUSTMENT ON VERTICAL PROFILES 15 3 DELAYED MODE QUALITY CONTROLS 16 3 1 DELAYED MODE PROCEDURES FOR PRESSURE 16 3 2 DELAYED MODE PROCEDURES FOR TEMPERATURE 16 3 3 DELAYED MODE PROCEDURES FOR SALINITY 17 3 3 1 INTRODUCTION 17 3 3 2 QUALITY CONTROL AND THE SEMI AUTOMATIC PART 18 3 3 3 SPLITTING THE FLOAT SERIES AND LENGTH OF CALIBRATION WINDOW 18 3 3 4 THE PI EVALUATION PART 20 3 3 5 ASSIGNING ADJUSTED SALINITY ERROR ESTIMATES AND QC FLAGS 21 3 3 6 SUMMARY FLOWCHART 23 3 3 7 WHAT TO SAY IN THE SCIENTIFIC CALIBRATION SECTION OF THE NETCDF FILE 24 3 3 8 OTHER PARAMETERS IN THE NETCDF FILE 24 3 3 9 TIMEFRAME FOR AVAILABILITY OF DELAYED MODE SALINITY DATA 25 3 3 10 REFERENCES 25 4 APPENDIX 26 4 1 REFERENCE TABLE 2 ARGO QUALITY CONTROL FLAG SCALE 26 4 2 COMMON INSTRUMENT ERRORS AND FAILURE MODES 27 History Date Com 01 01 2002 Creation of th
11. F format and forwarded to the Global Argo Servers Presently the TESAC code form is used to send the float data on the GTS see http www meds sdmm dfo mpo gc ca meds Prog_Int J COMM J COMM_e htm This code form only handles profile data and reports observations as a function of depth not pressure It is recommended that the UNESCO routines be used to convert pressure to depth Algorithms for computation of fundamental properties of seawater N P Fofonoff and R C Millard Jr UNESCO Technical Papers in Marine Science 44 1983 If the position of a profile is deemed wrong or the date is deemed wrong or the platform identification is in error then none of the data should be sent on the GTS For other failures only the offending values need be removed from the TESAC message The appropriate actions to take are noted with each test Argo data management quality control manual 30 11 2004 OO 2 1 2 Quality control tests 1 Platform identification Every centre handling float data and posting them to the GTS will need to prepare a metadata file for each float and in this is the WMO number that corresponds to each float ptt There is no reason why except because of a mistake an unknown float ID should appear on the GTS Action If the correspondence between the float ptt cannot be matched to the correct WMO number none of the data from the profile should be distributed on the GTS 2 Impossible date test The test requires that t
12. as salinity anomalies over several water masses e Using other independent oceanographic atlases to anticipate water mass changes that can occur along a float s path and that can be misinterpreted as sensor malfunction e Inspecting residuals from objective maps e Cross checking with nearby stable floats in cases of suspect sensor calibration offset If the PI is confident that sensor malfunction has occurred then the threshold for making an adjustment is when S is greater than 2 times whatever is reported in PSAL_ADJUSTED_ERROR By default this will be the error from the statistical methods but the PI can provide an alternative estimate of uncertainty if they have a basis for doing so Note that this guideline is to help the PI in deciding whether a slope or offset is statistically significant and so should be used to evaluate the entire float segment being fitted and not to single points Argo data management quality control manual 30 11 2004 T The lower bound on the size of an adjustment is the instrument acuracy At present there is no upper bound for the magnitude of salinity adjustment In cases where the float series has been split into separate segments the PI must ensure that the assembled adjustment for the entire float series is continuous within error bars except where the PI believes there is a genuine discontinuity see Step 5 in Section 3 3 3 This is to ensure that no artificial jump is introduced where the separ
13. ate segments join Adjustment continuity between separate float segments can be achieved by making adjustment in the transition phase even though the adjustment is below the 2 times error threshold limit In the following example the float series experiences sensor drift after a stable period The float series has been split for calibration However the float series has no discontinuity so the final assembled adjustment should be continuous Adjustment continuity is achieved by using model a and not b 3 3 5 Assigning adjusted salinity error estimates and qc flags After evaluating all available information the PI then assigns adjusted salinity values error estimates and delayed mode qc flags In Argo netcdf files these are found respectively in the parameters PSAL_ ADJUSTED PSAL_ADJUSTED_ERROR and PSAL_ADJUSTED_QC Please refer to Section 4 1 for definitions of the Argo qc flags in delayed mode The original float salinity and real time qc flags remain in the parameters PSAL and PSAL_QC and are never altered in delayed mode A Matlab based graphical user interface for interacting with Argo netcdf files has been developed by John Gilson at Scripps Institute of Oceanography Please contact jgilson ucsd edu The following is a set of guidelines for assigning values to PSAL_ADJUSTED PSAL_ADJUSTED_ERROR and PSAL_ADJUSTED_QC in Argo netcdf files When no delayed mode qc is available For example when the netcdf file is still i
14. cannot override a higher value from a previous test Example a QC flag 4 bad data set by Test 11 gradient test cannot be decreased to QC flag 3 bad data that are potentially correctable set by Test 15 grey list Argo data management quality control manual 30 11 2004 S mB 2 2 Argo Real time Quality Control Test Procedures on trajectories The following tests are applied in real time on trajectory data 1 Platform identification Every centre handling float data and posting them to the GTS will need to prepare a metadata file for each float and in this is the WMO number that corresponds to each float ptt There is no reason why except because of a mistake an unknown float ID should appear on the GTS Action If the correspondence between the float ptt cannot be matched to the correct WMO number none of the data from the profile should be distributed on the GTS 2 Impossible date test The test requires that the observation date and time from the float be sensible e Year greater than 1997 e Month in range 1 to 12 e Day in range expected for month e Hourin range 0 to 23 e Minute in range 0 to 59 Action If any one of the conditions is failed the cite should be flagged as bad data and none of the data from the profile should be distributed on the GTS 3 Impossible location test The test requires that the observation latitude and longitude from the float be sensible Action If either latitude or bngitude fai
15. cent depths gt 5 PSU Action Values that fail the test should be flagged as bad data and are removed from the TESAC distributed on the GTS If temperature and salinity values at the sme depth both fail both values should be flagged as bad data and then values for depth temperature and salinity should be removed from the TESAC distributed on the GTS 13 Stuck value test This test looks for all measurements of temperature or salinity in a profile being identical Action If this occurs all of the values of the affected variable should be flagged as bad data and are removed from the TESAC distributed on the GTS If temperature and salinity are affected all observed values are flagged as bad data and no report from this float should be sent to the GTS 14 Density inversion This test uses values for temperature and salinity at the same pressure level and computes the density The algorithm published in UNESCO Technical Papers in Marine Science 44 1983 referred to earlier should be used Densities are compared at consecutive levels in a profile Action If the density calculated at the greater pressure is less than that calculated at the lesser pressure both the temperature and salinity values should be flagged as bad data Consequently the values for depth temperature and salinity at this pressure level should be removed from the TESAC distributed on the GTS Argo data management quality control manual 30 11 2004 TOT 15 Grey
16. ction in the netCDF files to record the source of the error estimates and any other scientific calibration comments e g surface PRES is automatically reset to zero 3 2 Delayed mode procedures for temperature Delayed mode qc for TEMP is done by subjective assessment of vertical profile plots of TEMP vs PRES and PSAL vs TEMP This assessment should be done in relation to measurements from the same float as well as in relation to nearby floats and historical data The assessment should aim to identify a erroneous data points that cannot be detected by the real time qc tests and b vertical profiles that have the wrong shape Bad data points identified by visual inspection from delayed mode analysts are recorded with TEMP_ADJUSTED_QC 4 Please note that whenever PARAM_ADJUSTED_QC 4 e PARAM ADJUSTED FillValue e PARAM_ADJUSTED_ERROR FillValue Argo data management quality control manual 30 11 2004 TTY TEMP_ADJUSTED TEMP_ADJUSTED_ERROR TEMP _ADJUSTED_QC should be filled even when no adjustment is made In these cases TEMP_ADJUSTED_ERROR can be the manufacturer s quoted accuracy at deployment of float Please use the CALIB section in the netCDF files to record the source of the error estimates and any other scientific calibration comments 3 3 Delayed mode procedures for salinity 3 3 1 Introduction Delayed mode qc for PSAL described in this section are specifically for checking sensor drifts and off
17. d between profiles In all cases we would not expect the drift speed to exceed 3 m s If it does it means either a position or time is bad data or a float is mislabeled Using the multiple positions that are normally available for a float while at the surface it is often possible to isolate the one position or time that is in error Action If an acceptable position and time can be used from the available suite then the data can be sent to the GTS Otherwise flag the position the time or both as bad data and no data should be sent 6 Global range test This test applies a gross filter on observed values for temperature and salinity It needs to accommodate all of the expected extremes encountered in the oceans e Temperature in range 2 5 to 40 0 degrees C e Salinity in range 0 0 to 41 0 PSU Action If a value fails it should be flagged as bad data and only that value need be removed from distribution on the GTS If temperature and salinity values at the same depth both fail both values should be flagged as bad data and values for depth temperature and salinity should be removed from the TESAC being distributed on the GTS 7 Regional range test This test applies to only certain regions of the world where conditions can be further qualified In this case specific ranges for observations from the Mediterranean and Red Seas further restrict what are considered sensible values The Red Sea is defined by the region 10N 40E 20N 50E 3
18. e e PSAL_ADJUSTED_ERROR FillValue e PSAL_ADJUSTED_QC 4 The following are some cases where a flag 2 should be assigned e Adjustment is based on unsatisfactory reference database e Adjustment is based on a short calibration window because of sensor behaviour transition or end of sensor life and therefore may not be stable e Evaluation is based on insufficient information e Sensor is unstable e g magnitude of adjustment is too big or sensor has undergone too many sensor behaviour changes and therefore data are inherently of mediocre quality e When a float exhibits problems with its pressure measurements Argo data management quality control manual 30 11 2004 23 3 3 6 Summary flowchart Argo salinity sensor drift amp offset QC procedures Manual evaluation to detect anomalies on the relative profile such as spikes that are not detected in RT Remove anomalies that may skew the drift offset correction Use in least squares fit ea Use accepted methods and reference database split series and select See appropriate length for the sliding window to calculate recommended PSAL_ADJUSTED_ERROR re FillValue salinity adjustments PSAL_ADJUSTED_QC 4 Do not use in least squares fit Sensor drift and or offset has been detected and is significant No sensor error has been detected or sensor drift and or offset is not significant lt max 2 x statistical uncertainty ins
19. e document 28 03 2003 Changed lower limit of temperature in Med to 10 0 08 06 2004 Modified spike and gradient tests according to advice from Yasushi and added inversion test 24 10 2003 Real time qc test 15 and 16 proposed at Monterey data management meeting test 10 removed 07 10 2004 1 Real time and delayed mode manuals merged in Argo quality control manual 2 Frozen profile real time qc test 17 proposed at Southampton data management meeting 3 Deepest pressure real time qc test 18 proposed at Southampton data management meeting 4 Order list for the real time qc tests 5 Regional Global Parameter Test renamed Regional range test test 7 6 Grey list naming convention and format test 15 7 Real time qc on trajectories ment 23 11 2004 1 new introduction from Annie Wong pone 4 delayed mode quality control manual from Annie Wong 17 11 2005 2 3 added a section on real time salinity adjustment 3 1 added usage of SURFACE PRESSURE from APEX floats 3 3 5 added some more guidelines for PSAL_ADJUSTED_QC 2 3 3 8 clarified that PROFILE_ lt PARAM gt _QC should be recomputed when lt PARAM gt _ADJUSTED_QC becomes available See p 24 Authors Annie Wong Robert Keeley Thierry Carval and the Argo Data Management Team Argo data management quality control manual 30 11 2004 ET 1 Introduction This document is the Argo quality control user s manual The Argo data system has three levels of
20. e exhaustion of battery known as Energy Flu usually starts about 2 years after deployment The sharp drop in battery voltage related to Energy Flu as well as the low voltage towards the end of a float s natural life will cause spiky erratic measurements that will make it difficult for delayed mode analysts to determine where to split the float series and how to fit a slope Towards the end of float life low voltage will result in large drift followed by death Energy Flu will cause spikes that get worse and more frequent also followed by death 7 Druck sensor problem About 4 of SBE41s have experienced the Druck pressure sensor defect SeaBird has fixed this problem so this feature is only included in this section for identifying the profiles that have been affected The Druck sensor problem is caused by oil getting into the pressure sensor causing the sensor to report either PRES 3000 dbar or 3000 dbar The pressure sensor tries to adjust the piston to the fooled pressure and so Argo data management quality control manual 30 11 2004 T progressively becomes a surface drifter The problem usually starts with a profile that reports measurements from very close together depth levels Both temperature and salinity measurements are useless from that stage onward 8 Incorrect pressure sensor coefficient Incorrect scaling coefficient in the pressure sensor will give anomalous T S curves at depth The
21. eeded In cases where adjustments have been made examples of wordings for PSAL can be SCIENTIFIC_CALIB_EQUATION PSAL_ ADJUSTED PSAL S where S is calculated from a potential conductivity ref to 0 dbar multiplicative adjustment term r SCIENTIFIC_CALIB_COEFFICIENT r 0 9994 0 0001 vertically averaged S 0 025 0 003 SCIENTIFIC_CALIB_COMMENT Sensor drift detected Adjusted float salinity to statistical recommendation as in WJO 2003 with WOD2001 as the reference database Mapping scales used are 8 4 4 2 Length of sliding calibration window is 20 profiles The PI is free to use any wordings he she prefers Just be precise and informative Regardless of whether an adjustment has been made the date of calibration of each parameter PRES TEMP PSAL should be recorded in CALIBRATION_DATE 3 3 8 Other parameters in the netcdf file A history record should be appended to the HISTORY section of the netcdf file to indicate that the netcdf file has been through the delayed mode process Please refer to the Argo User s Manual 5 Using the History section of the Argo netCDF Structure on usage of the History section The parameter DATA_MODE should record D The parameter DATA_STATE_INDICATOR should record 2C The parameter DATE_UPDATE should record the date of last update of the netcdf file The parameters PROFILE lt PARAM gt _QC should be recomputed when lt PARAM
22. erators can evaluate the quality and adjustability of these bad data if they have a reason to do so Please refer to Section 4 1 for definitions of the Argo qc flags in real time In delayed mode float salinity that have PSAL_QC T 2 or 3 are further examined Anomalies in the relative vertical salinity profile such as measurement spikes and outliers that are not detected in real time are identified Of these anomalies those that will skew the least squares fit in the computation for drift and offset adjustments are excluded from the float series for evaluation of drifts and offsets These measurements are considered unadjustable in delayed mode Float salinity that are considered adjustable in delayed mode are assembled into time series or float series Sufficiently long float series are compared with statistical recommendations and associated uncertainties to check for sensor drifts and offsets These statistical recommendations and associated uncertainties are obtained by the accepted methods listed in Section 3 3 1 in conjunction with appropriate reference datasets These methods are semi automatic and have quantified uncertainties Drifts and offsets can be identified in the trend of AS over time where AS is the difference in salinity between float series and statistical recommendations If S a bt where t is time then a is the offset and b is the drift Note that these drifts and offsets can be sensor related or they ca
23. erranean Sea e Temperature in range 10 0 to 40 e Salinity in range 0 0 to 40 0 Argo data management quality control manual 30 11 2004 15 2 3 Argo Real time Salinity Adjustment on vertical profiles When delayed mode salinity adjustment see Section 3 3 becomes available for a float realtime data assembly centres will extract the adjustment from the latest D nc file as an additive constant and apply it to new salinity profiles If a better correction is available in realtime DACs can use that instead In this manner intermediate quality salinity profiles will be available to users in real time The values of this real time adjustment will be recorded in PSAL_ADJUSTED PSAL_ADJUSTED_QC will be filled with the same values as PSAL_QC PSAL_ADJUSTED_ERROR and all parameters in the SCIENTIFIC CALIBRATION section of the netCDF files will be filled with FillValue A HISTORY record will be appended to the HISTORY section indicating that real time salinity adjustment has been made DATA_MODE will record A When available real time adjusted values are distributed to the GTS instead of the original values Argo data management quality control manual 30 11 2004 TO 3 Delayed mode quality controls 3 1 Delayed mode procedures for pressure Delayed mode qc for PRES is done by subjective assessment of vertical profile plots of TEMP vs PRES and PSAL vs PRES This assessment should be done in relation to measurements from
24. fail the test require that e max deltaT lt 0 3 e min deltaT lt 0 001 e mean deltaT lt 0 02 e max deltaS lt 0 3 e min deltaS lt 0 001 e mean deltaS lt 0 004 Action if the profile fails the test all measurements for this parameter are flagged as bad data flag 4 If the float fails the test on 5 consecutive cycles it is inserted in the grey list 19 Deepest pressure test This test requires that the profile has pressures that are not higher than DEEPEST_PRESSURE plus 5 10 100 dbar to be defined DEEPEST PRESSURE value comes from the meta data file of the float Action If there is a region of incorrect pressures all pressures and corresponding measurements should be flagged as bad data flag 4 All pressures flagged as bad data and all of the associated temperatures and salinities are removed from the TESAC distributed on the GTS Argo data management quality control manual 30 11 2004 O na 2 1 3 Tests application order The Argo real time QC tests are applied in the order described in the following table Orderjtest number test name 19 Deepest pressure test 1 Platform Identification 2 Impossible Date Test Global Range Test 7 Regional Range Test 8iPressure Increasing Test of Spike Test i O t 10fTop and Bottom Spike Test removed 1 14 Density Inversion 17 16 Gross salinity or temperature sensor drift_ Frozen profile The QC flag value assigned by a test
25. he observation date and time from the float be sensible e Year greater than 1997 e Month in range 1 to 12 e Day in range expected for month e Hour in range 0 to 23 e Minute in range 0 to 59 Action If any one of the conditions is failed the date should be flagged as bad data and none of the data from the profile should be distributed on the GTS 3 Impossible location test The test requires that the observation latitude and longitude from the float be sensible Action If either latitude or longitude fails the position should be flagged as bad data and none of the data from the float should go out on the GTS e Latitude in range 90 to 90 e Longitude in range 180 to 180 4 Position on land test The test requires that the observation latitude and longitude from the float be located in an ocean Use can be made of any file that allows an automatic test to see if data are located on land We suggest use of at least the 5 minute bathymetry file that is generally available This is commonly called ETOPOS TerrainBase and can be downloaded from http www ngdc noaa gov mgeg global global html Action If the data cannot be located in an ocean the position should be flagged as bad data and they should not be distributed on the GTS Argo data management quality control manual 30 11 2004 TT 5 Impossible speed test Drift speeds for floats can be generated given the positions and times of the floats when they are at the surface an
26. list This test is implemented to stop the real time dissemination of measurements from a sensor that is not working correctly The grey list contains the following 7 items e Float Id e Parameter name of the grey listed parameter e Start date from that date all measurements for this parameter are flagged as bad and probably bad e End date from that date measurements are not flagged as bad or probably bad e Flag value of the flag to be applied to all measurements of the parameter e Comment comment from the PI on the problem e DAC data assembly center for this float Each DAC manages a black list sent to the GDACs The merged black list is available from the GDACs The decision to insert a float parameter in the grey list comes from the PI Example Float Id Parameter Start date End date Flag Comment Dac 1900206 PSAL 20030925 E ae ees e Grey list format ascii csv comma separated values e Naming convention xxx_greylist csv xxx DAC name ex aoml_greylist csv coriolis_greylist csv jma_greylist csv e PLATFORM PARAMETER START_DATE END_DATE QC COMMENT DAC 4900228 TEMP 20030909 3 AO 1900206 PSAL 20030925 3 IF 16 Gross salinity or temperature sensor drift This test is implemented to detect a sudden and important sensor drift It calculates the average salinity on the last 100 dbar on a profile and the previous good profile Only measurements with good QC are used Action if the difference between
27. ls the position should be flagged as bad data and none of the data from the float should go out on the GTS e Latitude in range 90 to 90 e Longitude in range 180 to 180 4 Position on land test The test requires that the observation latitude and longitude from the float be located in an ocean Use can be made of any file that allows an automatic test to see if data are located on land We suggest use of at least the 5 minute bathymetry file that is generally available This is commonly called ETOPOS TerrainBase and can be downloaded from http www ngdc noaa gov mge global global html Action If the data cannot be located in an ocean the position should be flagged as bad data and they should not be distributed on the GTS Argo data management quality control manual 30 11 2004 E T 5 Impossible speed test Drift speeds for floats can be generated given the positions and times of the floats when they are at the surface and between profiles In all cases we would not expect the drift speed to exceed 3 m s If it does it means either a position or time is bad data or a float is mislabeled Using the multiple positions that are normally available for a float while at the surface it is often possible to isolate the one position or time that is in error Action If an acceptable position and time can be used from the available suite then the data can be sent to the GTS Otherwise flag the position the time or both as bad data a
28. n be due to real ocean events PI evaluation is needed to distinguish between sensor errors and real ocean events OFFSET DRIFT AS AS time time 3 3 3 Splitting the float series and length of calibration window If a float exhibits changing behaviour during its lifetime the float series should be split into separate segments according to the different behaviours so that one float series segment does not contaminate the other during the least squares fit process e g the slowly fouling segment does not contaminate the stable segment Argo data management quality control manual 30 11 2004 SS 5959595959589 SSS The following is a step by step guide on how to deal with float series with changing behaviours 1 Identify different regimes in the float series These can be e Stable measurements no sensor drift including constant offsets e Sensor drift with a constant drift rate e Transition phase where drift rate changes rapidly e g a elbow region between stable measurements and constant drift b initial biocide wash off e Spikes 2 Split the float series into discrete segments according to these different regimes or when there are too many missing cycles Here is an example 2S Constant offset Discontinuity no transition phase Sensor drift with a constant drift rate Transition phase Spike Stable time 3 Choose length of sliding calibration window for each segmen
29. n realtime mode or when there is no LATITUDE LONGITUDE or JULD hence no statistical recommendation available Argo data management quality control manual 30 11 2004 22 e PSAL ADJUSTED FillValue e PSAL ADJUSTED _ERROR FillValue e PSAL ADJUSTED_QC FillValue For float salinity that are considered unadjustable in delayed mode For example large spikes or extreme behaviour where the relative vertical FS shape does not match good data These measurements are unadjustable e PSAL ADJUSTED FillValue e PSAL ADJUSTED_ERROR FillValue e PSAL_ADJUSTED_QC 4 For float salinity that are considered adjustable in delayed mode These measurements have a relative vertical FS shape tat is close to good data They are evaluated and adjusted for sensor drifts offsets and any other instrument errors 1 When no adjustment is needed e PSAL_ADJUSTED PSAL original value e PSAL_ADJUSTED_ERROR max statistical uncertainty instrument accuracy or uncertainty provided by PI e PSAL_ADJUSTED_QC 1 2 or 3 1i When an adjustment has been applied e PSAL_ADJUSTED value recommended by statistical analyses or adjustment provided by PI e PSAL_ADJUSTED_ERROR max statistical uncertainty instrument accuracy or uncertainty provided by PI e PSAL_ADJUSTED_QC 1 2 or 3 iii When the PI determines that float salinity are bad and unadjustable e PSAL ADJUSTED FillValu
30. nd no data should be sent 6 Global range test This test applies a gross filter on observed values for temperature and salinity It needs to accommodate all of the expected extremes encountered in the oceans e Temperature in range 2 5 to 40 0 degrees C e Salinity in range 0 0 to 41 0 PSU Action If a value fails it should be flagged as bad data and only that value need be removed from distribution on the GTS If temperature and salinity values at the same depth both fail both values should be flagged as bad data and values for depth temperature and salinity should be removed from the TESAC being distributed on the GTS 7 Regional range test This test applies to only certain regions of the world where conditions can be further qualified In this case specific ranges for observations from the Mediterranean and Red Seas further restrict what are considered sensible values The Red Sea is defined by the region 10N 40E 20N 50E 30N 30E 10N 40E and the Mediterranean Sea by the region 30N 6W 30N 40E 40N 35E 42N 20E 50N 15E 40N 5E 30N 6W Action Individual values that fail these ranges should be flagged as bad data and removed from the TESAC being distributed on the GTS If both temperature and salinity values at the same depth both fail then values for depth temperature and salinity should be removed from the TESAC being distributed on the GTS Red Sea e Temperature in range 21 7 to 40 0 e Salinity in range 0 0 to 41 0 Medit
31. ngton edu 2 Boehme and Send 2005 takes into account planetary vorticity in its estimates of background salinity and chooses a set of desirable isotherms for calculations This method suits float data from oceans with high spatial and temporal variabilities where water mass distribution is affected by topographic barriers and where multiple water masses exist on the same isotherm For the related software please contact Lars Boehme at 10284 st andrews ac uk Both methods require an adequate reference database and an appropriate choice of spatial and temporal scales as well as input of good adjusted float pressure temperature position and date of sampling Therefore analysts should first check the reference database for adequacy and determine a set of appropriate spatial and temporal scales before using these methods Operators should also ensure that other float measurements PRES TEMP LATITUTDE LONGITUDE JULD are accurate or adjusted before they deal with float salinity See Secions 3 1 and 3 2 for delayed mode procedures for PRES and TEMP Argo data management quality control manual 30 11 2004 O m 3 3 2 Quality control and the semi automatic part The real time qc procedures described in Section 2 issue a set of qc flags that warns users of the quality of the float salinity These are found in the variable PSAL_QC Float salinity with PSAL_QC 4 are bad data that are in general unadjustable However delayed mode op
32. onductivity cell will result in erroneously fresh salinity measurements When pollution washes off reversal of sensor drift trend can occur Delayed mode analysts need to be careful in splitting float series in such cases 3 Ablation events Any ablation of the conductivity cell such as etching scouring or dissolution of the glass surface will result in erroneously salty salinity measurements 4 Cell geometry changes The geometry of conductivity cells can change thus causing electrodes to change distance This will result in either an increase or decrease in salinity values 5 Cell circuit changes The circuit within the conductivity cell contains capacitors and resistors Changes to any of these electrical components will affect electrical conductivity and thus will give erroneous fresh or salty salinity measurements Electrical complication can result in sensor drifts that have varying drift rates e g drift rates can change fom slow and linear to exponential Usually jumps in salinity measurements are an indication of electrical malfunction If electrical complication is suspected delayed mode analysts should check the shape of the vertical salinity profiles for adjustability Usually the vertical profiles after a measurement jump are wrong and so are uncorrectable 6 Low voltage at end of float life and Energy Flu APEX floats often experience a sudden rapid decrease in available battery energy reserves This prematur
33. sets Analysts should be aware that there are other instrument errors and should attempt to identify and adjust them in delayed mode If a measurement has been adjusted for more than one instrument error analysts should attempt to propagate the uncertainties from all the adjustments The free moving nature of profiling floats means that most float salinity measurements are without accompanying in situ ground truth values for absolute calibration such as those afforded by shipboard CTD measurements Therefore Argo delayed mode procedures for checking sensor drifts and offsets in salinity rely on reference datasets and statistical methods However since the ocean has inherent spatial and temporal variabilities these drift and offset adjustments are subject to statistical uncertainties Users therefore should include the supplied error estimates in their usage of Argo delayed mode salinity data Two methods are available for detecting sensor drifts and offsets in float salinity and for calculating adjustment estimates and related uncertainties 1 Wong Johnson Owens 2003 estimates background salinity on a set of fixed standard isotherms then calculates drifts and offsets by time varying weighted least squares fits between vertically interpolated float salinity and estimated background salinity This method suits float data from open tropical and subtropical oceans For the related software please contact Annie Wong at awong ocean washi
34. t These can be e Long window 6 months or greater for the stable regime or highly variable regimes where a long window is required to average over oceanographic variability to detect slow sensor drift or period of constant drift rate e Short window can be as short as 10 days for the transition phase e Zero length window for spikes That is adjust single profile 4 Select temperature levels for exclusion from least squares fit e g seasonal mixed layer highly variable water masses Argo data management quality control manual 30 11 2004 T 5 Calculate proposed adjustment for each segment The assembled proposed adjustments for the entire float series should be continuous and piecewise linear within error bars except where the delayed mode operator believes there is a genuine discontinuity In general the delayed mode operator should aim to use as long a calibration window as possible because a long calibration window where the least squares fit is calculated over many cycles will average over oceanographic noise and thus give a stable calibration Hence splitting the float series into short segments is to be avoided short segments mean short calibration windows hence unstable calibrations 3 3 4 The PI evaluation part The PI here PI means Principal Investigator or responsible persons assigned by the PI should first check that the statistical recommendations are appropriate This is because the semi a
35. t the date of the update The profile index file on the GDACs contains the DATE_UPDATE information along with other information for every file on the GDACs and can be used to monitor updates The profile index file is maintained in the top level GDAC directory and is named ar_index_global_prof txt index files also exist for the meta data and trajectory files 3 3 10 References Bohme L and U Send 2005 Objective analyses of hydrographic data for referencing profiling float salinities in highly variable environments Deep Sea Research II 52 3 4 651 664 Wong A P S G C Johnson and W B Owens 2003 Delayed mode calibration of autonomous CTD profiling float salinity data by O0 S_ climatology Journal of Atmospheric and Oceanic Technology 20 308 318 Argo data management quality control manual 30 11 2004 26 4 Appendix 4 1 Reference Table 2 Argo quality control flag scale This table describes the Argo qc flag scales Please note that this table is used for dl measured parameters This table is named Reference Table 2 in the Argo User s Manual n Meaning Real time comment Delayed mode comment No QC was performed No QC was performed No QC was performed The adjusted value is statistically consistent and a statistical error estimate is 1 Good data All Argo real time QC tests passed supplied 2 data Probably good data Probably good data Test 15 or Test 16 or Test 17 failed and all other real time QC
36. trument accuracy gt max 2 x statistical uncertainty instrument accuracy Apply adjustment No eeiusinneni meeles or declare unadjustable PSAL_ADJUSTED PSAL original value PSAL_ADJUSTED PSAL_ADJUSTED_ERROR value recommended by statistical analyses or max statistical uncertainty instrument accuracy adjustment provided by PI or uncertainty provided by PI PSAL_ADJUSTED_ERROR PSAL_ADJUSTED_QC 1 2o0r3 max statistical uncertainty instrument accuracy or uncertainty provided by PI PSAL_ADJUSTED_QC 1 20r3 OR PSAL_ADJUSTED FillValue PSAL_ADJUSTED_ERROR FillValue Last update 19 Apr 05 PSAL_ADJUSTED_QC 4 Argo data management quality control manual 30 11 2004 T T 3 3 7 What to say in the scientific calibration section of the netcdf file Within each single profile Argo netcdf file is a scientific calibration section that records details of delayed mode adjustments In this scientific calibration section for every parameter listed in PARAMETER PRES TEMP PSAL there are four fields to record scientific calibration details e SCIENTIFIC_CALIB_ EQUATION e SCIENTIFIC_CALIB_COEFFICIENT e SCIENTIFIC_CALIB_ COMMENT e CALIBRATION_DATE In cases where no adjustment has been made SCIENTIFIC_CALIB_EQUATION and SCIENTIFIC_CALIB_ COEFFICIENT shall be filled by their respective FillValue SCIENTIFIC_CALIB_ COMMENT shall contain wordings that describe the evaluation e g No adjustment is n
37. utomatic methods cannot distinguish ocean features such as eddies fronts and water mass boundaries Near such ocean features semi automatic statistical methods are likely to produce erroneous estimations The associated uncertainties reflect the degree of local variability as well as the sparsity of reference data used in the statistical estimations However these associated uncertainties are sensitive to the choice of scales Hence the PI also needs to determine that the associated uncertainties are realistic The PI then determines whether the proposed statistical adjustment is due to sensor malfunction or ocean variability Care should be taken to not confuse real ocean events with sensor drifts and offsets This is done by inspecting as long a float series as possible and by evaluating all available independent information Some of the diagnostic tools can include e Inspecting the trend of AS over time Trends that reverse directions or oscillate are difficult to explain in terms of systematic sensor malfunction These are often caused by the float sampling oceanographic features e g eddies fronts etc that are not adequately described in the reference database e Visual check of float trajectory with reference to oceanographic features such as eddies and rings that can introduce complications to the semi automatic methods e Inspecting contour plots of float salinity anomaly time series Systematic sensor malfunction should show up
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