Argo QC with an emphasis on the North Atlantic

Justin BuckBritish Oceanographic Data Centre

Joseph Proudman Building6 Brownlow Street

Liverpool L3 5DA, UK

Outline

QC of Argo data• Overview of processing steps• Real-time QC• Near- real-time QC• Delayed mode QC• Global consistency checks (GDAC level)Status of the QC of Argo in the North Atlantic (NA)• Status of profiles in the North Atlantic• Feed back from the NA Argo Regional CentreOther points• Sources of information on Argo QC

Argo processing stages

• Flow chart describing the real time data flow through BODC

• Delayed mode processing fits in the visual screening loop

Real-time QC

• Automated process, all data put through these tests before real-time versions of data submitted to GTS and GDACs

• Tests agreed internationally by the Argo Data Management Team (ADMT)

• Summarised in the Argo QC manual (http://www.argodatamgt.org/Media/Argo-Data-Management/Argo-Documentation/General-documentation/Argo-Quality-Control-manual-October-2009 pages 5-16

)• A new ‘jump test’ to be implemented by BODC in coming

year with results going to ADMT in 2010 and potential for implementation by all countries

• Process also applies calibrations where appropriate (e.g. real time pressure correction)

Argo QC flags

Flag Description0 No QC was performed

1 Good data

2 Probably good data

3 Bad data that are potentially correctable

4 Bad data

5 Value changed (not applicable to calibration changes where flag should be 1-4)

8 Interpolated value

9 Missing value

A full description on the usage of Argo QC flags is in the Argo QC manual.

Real-time QC

Order Test no. Description Order Test no. Description1 19 Deepest pressure

test11 10 Top and Bottom

Spike Test : removed

2 1 Platform identification

12 11 Gradient Test

3 2 Impossible date 13 12 Digit Rollover Test 4 3 Impossible

location14 13 Stuck Value Test

5 4 Position on land 15 14 Density Inversion 6 5 Impossible speed 16 15 Grey List

7 6 Global range 17 16 Gross salinity or temperature sensor drift

8 7 Regional range 18 18 Frozen profile 9 8 Pressure

increasing19 17 Visual QC (near-

real-time)10 9 Spike test

Near-real-time

• Profiles from UK floats are screened in near-real-time by BODC, this practice does vary by data centre though.

Delayed-mode QC (DMQC)

• Target date is within 6-12 moths of a profile being acquired

• Should include a re-screen of the profiles• Uses a more refined pressure correction to profiles

than is applied in real time• Methods well defined and documented in the Argo

QC manual• However, some centres (including BODC) have a

long standing backlog in their DMQC

Owens Wong (OW) DMQC software

• Used for the DMQC of salinity, and assumes the temperature good

• Quoted accuracy in salinity after data has passed through OW can be as good as 0.01 (psu, non-dimensional)

Global consistency checks

• SSH from altimetry Vs DHA derived from Argo profiles• ftp://ftp.ifremer.fr/ifremer/argo/etc/argo-ast9-item13-AltimeterComparison/figures

Global consistency checks

• Float inter-comparison run by Ifremer• Uses ARIVO climatology and OW software

North Atlantic Argo status

• North Atlantic 20S-80N, 75W-15E, time span 2004-date, holdings at USGODAE GDAC as of 26-Nov-2009• Total number of Argo profiles 83670• Total number of delayed mode profiles 46994• BODC has not started DMQC of its NA floats yet because

of time/funding constraints• Pressure issues

• See ADMT10 and DMQC3 workshop meeting reports (http://www.argodatamgt.org/Data-Mgt-Team/Meetings-and-reports)

• Several types of pressure issue• Drifts (~5-10 dBar)• Truncated negative pressures (i.e. Unknown drifts)• Druck micro-leak failures

• Aim is for all data centres to have these resolved before the Argo Science team meeting in early 2010

North Atlantic Argo status

• Table showing number of delayed mode profiles by year (source US GODAE Argo GDAC as of 26-Nov-2009)

Year Total number of profiles

Number of delayed mode profiles

% profiles through DMQC

2004 9594 5993 62%

2005 11337 6814 60%

2006 14869 8729 59%

2007 13782 10277 75%

2008 12808 8685 68%

2009* 15454 3273 21%

* The reason the percentage is lower in 2009 is profiles are not officially eligible for DMQC until 6 months after collection

NA Argo Regional Centre (ARC)

• Run by Coriolis, France (Contacts are Sylvie Pouliquen/Virginie Thierry)

• NA ARC activities that are particularly relevant to this discussion are:• Ensure consistency of the Argo data from the North

Atlantic, independent of float provider, using statistical tools to detect potential outliers and provide feedback to DACs and PIs

• Product delivery: The main product of the RDAC will be a consistent Argo delayed mode dataset for the North Atlantic. However some scientific products such as temperature and salinity weekly analysis, improved mean sea state of the ocean for Argo period, currents calculated from floats , .... will be made available though NA-ARC with clear documentation.

NA Argo Regional Centre (ARC)

• Sylvie Pouliquen’s comments on Argo QC in the North Atlantic are as follows:• ARCs are not yet doing all the consistency checks that

we would like to be performed:• APEX pressure correction are not applied yet by all

groups neither in Real time nor in delayed mode but all teams are working on it and ADMT10 recommendation will be implemented in the coming months.

• SOLO problem is partially corrected by WHOI but WHOI is working on delayed mode processing

• Consistency checks are applied at Coriolis are done on real-time data but  there is work to be done on delayed mode data

Sources of information

• Argo Data Management Team (ADMT)• http://www.argodatamgt.org/ • Includes:

• QC Documentation• Status statistics from produced by the French GDAC

• North Atlantic Argo Regional Centre• http://www.argodatamgt.org/Argo-regional-Centers/North-Atlanti

c-ARC

The PRES_ERROR field question

• The issue of what to set the PRES_ERROR field to was discussed at length during ADMT10.

• This was with respect to floats where the pressure has drifted considerably.

• The accuracy of the sensor is 2.4 dBar (typically used as the error in floats without issues), but as a community we would like to highlight this float has drifted significantly.

• What as part of the user community would you like/expect the PRES_ERROR field to be set to in such cases?