Metadata Report for BODC Series Reference Number 649131


Metadata Summary

Data Description

Data Category Currents -subsurface Eulerian
Instrument Type
NameCategories
Teledyne RDI Ocean Surveyor 150kHz vessel-mounted ADCP  current profilers
Instrument Mounting research vessel
Originating Country United Kingdom
Originator Dr Gregory Lane-Serff
Originating Organization University of Manchester School of Mechanical, Aerospace and Civil Engineering
Processing Status banked
Project(s) Autosub Under Ice
 

Data Identifiers

Originator's Identifier 097ADP060D
BODC Series Reference 649131
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 2005-03-01 00:00
End Time (yyyy-mm-dd hh:mm) 2005-03-01 23:58
Nominal Cycle Interval 120.0 seconds
 

Spatial Co-ordinates

Southernmost Latitude 74.66100 S ( 74° 39.7' S )
Northernmost Latitude 74.24480 S ( 74° 14.7' S )
Westernmost Longitude 36.45600 W ( 36° 27.4' W )
Easternmost Longitude 32.14500 W ( 32° 8.7' W )
Positional Uncertainty 0.0 to 0.01 n.miles
Minimum Sensor Depth 18.0 m
Maximum Sensor Depth 522.0 m
Minimum Sensor Height -
Maximum Sensor Height -
Sea Floor Depth -
Sensor Distribution Sensor fixed, measurements made at fixed depths - The sensor is at a fixed depth, but measurements are made remotely from the sensor over a range of depths (e.g. ADCP measurements)
Sensor Depth Datum Instantaneous - Depth measured below water line or instantaneous water body surface
Sea Floor Depth Datum -
 

Parameters

BODC CODE Rank Units Short Title Title
DBINAA01 0 Metres BinDep Depth below sea surface (ADCP bin)
AADYAA01 1 Days Date(Loch_Day) Date (time from 00:00 01/01/1760 to 00:00 UT on day)
AAFDZZ01 1 Days Time(Day_Fract) Time (time between 00:00 UT and timestamp)
ALATZZ01 1 Degrees Lat Latitude north
ALONZZ01 1 Degrees Lon Longitude east
ASAMAS01 2 Decibels ADCPSA Signal return amplitude from the water body by shipborne acoustic doppler current profiler (ADCP)
LCEWAS01 2 Centimetres per second CurrVelE_ADCP Eastward current velocity (Eulerian) in the water body by shipborne acoustic doppler current profiler (ADCP)
LCNSAS01 2 Centimetres per second CurrVelN_ADCP Northward current velocity (Eulerian) in the water body by shipborne acoustic doppler current profiler (ADCP)
LERRAS01 2 Centimetres per second ADCPER Current velocity error in the water body by shipborne acoustic doppler current profiler (ADCP)
LRZAAS01 2 Centimetres per second ADCPVC Upward current velocity in the water body by shipborne acoustic doppler current profiler (ADCP)
PCGDAP01 2 Percent Percent_Good_(ADCP) Acceptable proportion of signal returns by acoustic doppler current profiler (ADCP)
 

Definition of Rank

  • Rank 1 is a one-dimensional parameter
  • Rank 2 is a two-dimensional parameter
  • Rank 0 is a one-dimensional parameter describing the second dimension of a two-dimensional parameter (e.g. bin depths for moored ADCP data)

Problem Reports

No Problem Report Found in the Database


Data Access Policy

Open Data supplied by Natural Environment Research Council (NERC)

You must always use the following attribution statement to acknowledge the source of the information: "Contains data supplied by Natural Environment Research Council."


Narrative Documents

RD Instruments- Ocean Surveyor 150kHz Vessel mounted ADCP.

Long-Range Mode
Vertical Resolution Cell Size 3 Max. Range (m) 1 Precision (cm/s) 2
4m 325 - 350 30
8m 375 - 400 19
High-Precision Mode
Vertical Resolution Cell Size 3 Max.Range (m) 1 Precision (cm/s) 2
4m 200 - 250 12
8m 220 - 275 9

1 Ranges at 1 to 5 knots ship speed are typical and vary with situation.
2 Single-ping standard deviation.
3 User's choice of depth cell size is not limited to the typical values specified.

Profile Parameters

Bottom Track

Maximum altitude (precision <2cm/s): 600m

Echo Intensity Profile

Dynamic range: 80dB
Precision: ±1.5dB

Transducer & Hardware

Beam angle: 30°
Configuration: 4-beam phased array
Communications: RS-232 or RS-422 hex-ASCII or binary output at 1200 - 115,200 baud
Output power: 1000W

Standard Sensors

Temperature (mounted on transducer)

Environmental

Operating temperature: -5° to 40°C (-5° to 45°C)*
Storage temperature: -30° to 50°C (-30° to 60°C)*

*later instruments have greater range.

Web Page

Further details can be found in the manufacturer's website or in the specification sheet .

Instrument Description

RRS James Clark Ross 150 kHz vessel-mounted ADCP

The RRS James Clark Ross carries a hull-mounted RDI 153.6 kHz Acoustic Doppler Current Profiler (ADCP), serial number 361. The ADCP is recessed into the hull behind a sea chest, which contains 90% deionised water and 10% ethylene glycol. A 33 mm sheet of Low Density PolyEthylene (LDPE) closes the underside of the chest. The effective depth of the transducer is 6 m (JR97 cruise report).

The ADCP is run through a PC (Pentium II) in the UIC, using version 2.48 of the RDI Data Acquisition Software (DAS) and version 17.07 of the firmware. The operation of this system is described in the JR97 cruise report.

References

JR97 Cruise Report , Autosub Under Ice Cruise to the southern Weddell Sea, RRS James Clark Ross, 3 February to 11 March 2005

BODC processing

The originator's files used for transfer were NOC Pstar format calibrated, gridded depth-dependent data, filenames 097adp[jday]d.abs , where [jday] is the day number of the file. There were 36 files supplied to BODC spanning 13:35:59 3rd February 2005 to 23:50:59 10th March 2005. The data were transferred (using transfer process tr339) to QXF format, a BODC-defined subset of NetCDF and BODC's format for 2-dimensional datacycle storage. Pstar null data were set to the appropriate absent data values for the code in the BODC parameter dictionary. Data values outside the range of the BODC parameter codes were automatically flagged as 'M' by the transfer. The following table shows how the variables within the Pstar files were mapped to BODC parameter codes:

Originator's Variable Originator's Units Description BODC Parameter Code BODC Parameter Units Comments
bindepth m Bin depth DBINAA01 m none
absve cm s -1 E-W current velocity (VMADCP) LCEWAS01 cm s -1 none
absvn cm s -1 N-S current velocity (VMADCP) LCNSAS01 cm s -1 none
velvert cm s -1 VMADCP vertical current velocity (+ve up) LRZAAS01 cm s -1 none
velerr cm s -1 Error velocity (VMADCP) LERRAS01 cm s -1 none
ampl db VMADCP signal return amplitude ASAMAS01 db none
good % Percent Good Signal Return (Shipborne ADCP) PCGDAP01 % none
lat ° Latitude north (Ashtech GPS) ALATAS01 ° none
lon ° Longitude east (Ashtech GPS) ALONAS01 ° none

Pstar variables present in the files but not mapped for transfer included: evelcal, nvelcal, ve, vn, a-ghdg and distrun. These were excluded on the grounds that that they were either intermediate processing stages or available in other datasets (i.e. underway navigation).

The reformatted data were visualised using the in-house EDSERPLO software. Suspect data wehe marked by adding an appropriate quality control flag, missing data by both setting the data to an appropriate value and setting the quality control flag. The navigation channels were checked against underway data for the same cruise that was received separately.

Originator's Data Processing

These notes have been adapted from the cruise report listed in the references. For a complete originator's processing description, please refer to the cruise report.

Sampling Strategy

The shipboard ADCP was run continuously during the cruise, apart from short breaks to reconfigure the settings. Throughout the cruise it was configured to run with 64, eight metre bins. The center of the first bin was effectively at a depth of 18 m, and thus the center of the last bin was at 522 m. In practice, good velocities were obtained down to about bin 40 to 50 (330 to 410 m), depending on conditions (the clearer waters near the ice shelf presumably having fewer scatterers). When bottom tracking was enabled (as it generally was in shallow waters), good bottom tracking velocities were obtained down to depths of 600 to 700 m.

The ADCPs bottom tracking mode was used initially, while the water was shallow enough for it to work (shallower than 600 m) to provide information for calibration, but was turned off once in deeper water. Having bottom tracking on reduces the number of water tracking pings, since the ADCP is spending half its time doing bottom pings.

The ADCP was monitored as part of general watch keeping during the cruise as follows:

Data Processing

Originator's processing used the NOC (National Oceanography Centre, Southampton, UK) pstar system. Pstar is a set of Fortran scripts that read and process data from the instrumentation and ship's systems. Output files from pstar processing are in a binary format. Specific edits relating to the handling of bin depths and the processing of partial days of data were made to the pstar scripts for this cruise and are described in the cruise report. The sequence of pstar scripts used in the processing was as follows:

  1. gyroexec0, to read the data (ship's heading) from the ship's gyro compass.
  2. ashexec0, to read the data from the ship's Ashtech GPS system for correction of the gyro headings.
  3. ashexec1, combines the Ashtech and gyro data.
  4. ashexec2, quality controls Ashtech and gyro data.
  5. navexec0, reads the ship's 'bestnav' data (the combined navigation data from the ship's GPS systems).
  6. navexec1, averages and filters the bestnav data.
  7. adpexec0, reads the ADCP data and produces water track and bottom track files. Navigation processing steps (including checks on the clock drifts) for the previous day needed to be complete before this could be run.
  8. adpexec1, adjusts the timing of the ADCP data for clock drifts.
  9. adpexec2, corrects for the errors in the gyro headings, making use of the differences between the gyro and Ashtech headings calculated in the ashexec pstar sequence (steps 2 to 4).
  10. adpexec3, applies the data calibration velocity magnitude scale and angle offset (ADCP alignment), these were hardcoded within the script. Calibration of the ADCP is described in the next subsection.
  11. adpexec4, subtracts the ship's velocity from the ADCP data to give absolute water velocities, producing files 097adp[jday]d.abs and 097bot[jday]d.abs .

Field Calibrations

Both the magnitude (scale correction) and direction of the ADCP data were calibrated. Errors in the magnitude of the measured velocities are caused by variations in the sound speed. The ADCP was calibrated by comparing ground speed from the bottom tracking ADCP velocities with ground speed derived from the GPS. Errors in the direction of measured velocities were corrected for the alignment of the ADCP (rotation by 1.78 degrees clockwise). Most errors in the direction of velocities are because the ADCP uses ship's heading from the gyro. These were corrected during the pstar processing by using data from the Ashtech GPS system.

Initial calibrations were carried out based on bottom-tracked data obtained on leaving the Falkland Islands, and further calibrations were carried out in the Fimbul Ice Shelf area and in the Filchner Depression. It was essential that at least the ADCP speeds (if not direction) were recalibrated when moving into waters of different temperature.

The scale factor from the initial data near the Falkland Islands was 1.0265, and this value was used for Julian days 34 to 37 on the southward journey and days 66 onward on the return journey (nominally 'warm' waters). For the bulk of the cruise, a value of 1.0409 was used, based on measurements around the Fimbul Ice Shelf. This was checked periodically, including in shallower waters around the Filchner Depression, and was not found to change significantly (though the four decimal places in the value exaggerates the accuracy: changes of ±0.002 or so over the course of a single day are not uncommon).

References

JR97 Cruise Report , Autosub Under Ice Cruise to the southern Weddell Sea, RRS James Clark Ross, 3 February to 11 March 2005

General Data Screening carried out by BODC

BODC screen both the series header qualifying information and the parameter values in the data cycles themselves.

Header information is inspected for:

Documents are written by BODC highlighting irregularities which cannot be resolved.

Data cycles are inspected using time or depth series plots of all parameters. Currents are additionally inspected using vector scatter plots and time series plots of North and East velocity components. These presentations undergo intrinsic and extrinsic screening to detect infeasible values within the data cycles themselves and inconsistencies as seen when comparing characteristics of adjacent data sets displaced with respect to depth, position or time. Values suspected of being of non-oceanographic origin may be tagged with the BODC flag denoting suspect value; the data values will not be altered.

The following types of irregularity, each relying on visual detection in the plot, are amongst those which may be flagged as suspect:

If a large percentage of the data is affected by irregularities then a Problem Report will be written rather than flagging the individual suspect values. Problem Reports are also used to highlight irregularities seen in the graphical data presentations.

Inconsistencies between the characteristics of the data set and those of its neighbours are sought and, where necessary, documented. This covers inconsistencies such as the following:

This intrinsic and extrinsic screening of the parameter values seeks to confirm the qualifying information and the source laboratory's comments on the series. In screening and collating information, every care is taken to ensure that errors of BODC making are not introduced.


Project Information

AutoSub Under Ice (AUI) Programme

AutoSub was an interdisciplinary Natural Environment Research Council (NERC) thematic programme conceived to investigate the marine environment of floating ice shelves with a view to advancing the understanding of their role in the climate system.

The AUI programme had the following aims:

Following the invitation of outline bids and peer review of fully developed proposals, eight research threads were funded as part of AUI:

Physical Oceanography

Glaciology and Sea Ice

Geology and Geophysics

Biology

The National Oceanography Centre Southampton (NOCS) hosted the AUI programme with ten further institutions collaborating in the project. The project ran from April 2000 until the end of March 2005, with some extensions to projects beyond this date because of research cruise delays. The following cruises were the fieldwork component of the AUI project:

Table 1: Details of the RRS James Clark Ross AUI cruises.

Cruise No. Cruise No. synonyms Dates Areas of study
JR20030218 JR84 28 February 2003 to 4 April 2003 Amundsen Sea, Antarctica
JR20040813 JR106, JR106a, JR106N (North) 10 August 2004 to 30 August 2004 Northeast Greenland Continental Shelf, Greenland
JR20040830 JR106b, JR106S (South) 30 August 2004 to 16 September 2004 Kangerlussuaq Fjord, Greenland
JR20050203 JR97, JR097 3 February 2005 to 11 March 2005 Fimbul Ice Shelf and Weddell Sea, Antarctica . This cruise was redirected from the Filcner-Ronne Ice Shelf to the Fimbul Ice Shelf because of unfavourable sea-ice conditions.

All the cruises utilised the AutoSub autonomous, unmanned and untethered underwater vehicle to collect observations beneath sea-ice and floating ice shelves. AutoSub can be fitted with a range of oceanographic sensors such as:

In addition to use of AutoSub during each cruise measurements were taken from ship. These varied by cruise but included:

The AutoSub project also included numerical modelling work undertaken at University College London, UK.

The project included several firsts including the first along-track observations beneath an ice shelf using an autonomous underwater vehicle. The AutoSub vehicle was developed and enhanced throughout this programme and has now become part of the NERC equipment pool for general use by the scientific community. Further information for each cruise can be found in the respective cruise reports (links in Table 1).


Data Activity or Cruise Information

Cruise

Cruise Name JR20050203 (JR97)
Departure Date 2005-02-03
Arrival Date 2005-03-11
Principal Scientist(s)Keith Nicholls (British Antarctic Survey)
Ship RRS James Clark Ross

Complete Cruise Metadata Report is available here


Fixed Station Information


No Fixed Station Information held for the Series


BODC Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:

Flag Description
Blank Unqualified
< Below detection limit
> In excess of quoted value
A Taxonomic flag for affinis (aff.)
B Beginning of CTD Down/Up Cast
C Taxonomic flag for confer (cf.)
D Thermometric depth
E End of CTD Down/Up Cast
G Non-taxonomic biological characteristic uncertainty
H Extrapolated value
I Taxonomic flag for single species (sp.)
K Improbable value - unknown quality control source
L Improbable value - originator's quality control
M Improbable value - BODC quality control
N Null value
O Improbable value - user quality control
P Trace/calm
Q Indeterminate
R Replacement value
S Estimated value
T Interpolated value
U Uncalibrated
W Control value
X Excessive difference

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:

Flag Description
0 no quality control
1 good value
2 probably good value
3 probably bad value
4 bad value
5 changed value
6 value below detection
7 value in excess
8 interpolated value
9 missing value
A value phenomenon uncertain