processing and quality checks of shipboard adcp

MAY 3-5 2004 ICES – MDM 2004, BRUSSELS

Processing and Quality Checks of Shipboard

ADCP

Michèle FICHAUT, IFREMER/SISMER

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Ship and Equipment

Three IFREMER ShipsL’ATALANTE : NB 75 and NB 300 THALASSA : NB75 and BB 150SUROÎT : BB 150

One Hydrographic Office ShipBEAUTEMPS-BEAUPRE : NB 38 and BB 150

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Data transmission

Since 2001, standard configuration on the IFREMER vessels

Raw data at SISMER at the end of the cruiseErrors in the acquisition are detected when processing the data

Since 2004, Beautemps-Beaupré transmits ADCP data each day in real time

Data are processed at the end of the cruiseBut errors in the acquisition can be detected on the first file and corrected directly onboard

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Processing

Software CASCADE developed in IFREMER by the Laboratory of Physical Oceanography (Matlab)4 steps for the processing :

Reformatting raw data into NetCDF Generation of processed files (attitude and time corrections, calculation of terrestrial coordinates, filtering, means)Ground speed calculationQuality checks of the data

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Quality checks of the data

Flags are attributed to the numerical values automatically and visually (flag 9)

1 Good data2 Doubtf ul data (out liers)3 Spikes4 Gradient > 0.05 cm/ s5 Vert ical current speed > 30 cm/ s6 Horizontal current speed component > 4 m/ s7 Missing data8 Data under the bottom (bottom ping)9 Data visually rejected (inconsistent)

10 Data under the bottom (compared to gridded bathymetry)

ADCP1 Good2 Probably good3 Doubtf ul4 False5 Modifi ed6 Not used7 Not used8 Not used9 Missing value

GTSPP

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Example of QC

Cruise of the BEAUTEMPS-BEAUBRE in the Red Sea , Aden Gulf and Oman Sea

Corresponding quality flags for the whole cruise

Inconsistent values -> Flag 9

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Presentation of the data

For one cruise, one or several sections are defined

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Images of the sections

Section 1, in the Red Sea

E/W horizontal current speed componentN/S horizontal current speed componentCurrent vertical speed

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Whole cruise’s vector plots

0 – 100 m 100 – 300 m

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Section’s vector plotsEddies in the superficial water (0-100m and 100-300m)Current aligned on the central valley in the deepest part (300-600 m)

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Detected errors

Errors detected at the beginning of data processing :

ADCP time is wrong and cannot be related to the navigationRaw data files are too big to be processed by the software : typically the standard procedure is one raw data file per one day of cruise maximum (12 hours is the optimal size).

Errors detected after data processingStrong correlation between current speed and ship velocityUnrealistic current vectors

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Example of wrong data (1)

Detected with correlation between ship velocity and current speed

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Example of wrong data (2)

Detected with section’s vector plots

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Data distributionSince 2001 : 49 IFREMER cruises (21 processed), 3 SHOM cruises (all processed)

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Data volume

52 cruises : Raw data : 49 Gigabytes ~= 1 gigabyte per cruise

Data dissemination : between 1 to 100 Mb per cruise

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Provinding data

One NetCDF file per cruiseDate/time, Latitude, Longitude, Depth, N/S, E/W , Vertical current speed, Echo intensity

One tar file with figuresSection map, images and vector plots of the sections

One reportInformation about data collectionInformation about the quality checks and the processing proceduresAny problem encountered with the data

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Conclusive remarks and questions

Not fully compliant with MDM guidelines for ADCP:

Dissemination format is NetCDF in stead of ASCII

There is no international exchange for ADCP data :

Is it worth doing one?What about the WDCA ?

What do other members do with ADCP shipboard data if they have some ?

processing and quality checks of shipboard adcp

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