Transcript [Title of presentation]

Argo QC with an emphasis
on the North Atlantic
Justin Buck
British Oceanographic Data Centre
Joseph Proudman Building
6 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 Centre
Other 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/Generaldocumentation/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
Description
0
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.
Description
1
19
Deepest pressure
test
11
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
location
14
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
increasing
19
17
Visual QC (nearreal-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/Meetingsand-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/NorthAtlantic-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?