Metadata Report for BODC Series Reference Number 670089

• Metadata Summary

• Problem Reports

• Data Access Policy

• Narrative Documents

• Project Information

• Data Activity or Cruise Information

• Fixed Station Information

• BODC Quality Flags

• SeaDataNet Quality Flags

Metadata Summary

Problem Reports

No Problem Report Found in the Database

RAPID Cruise D279 75KHZ VMADCP Data Quality Report

Data visually inspected and found to be of generally good quality with only a few isolated suspect data points flagged.

Data Access Policy

Open Data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

If the Information Provider does not provide a specific attribution statement, or if you are using Information from several Information Providers and multiple attributions are not practical in your product or application, you may consider using the following:

"Contains public sector information licensed under the Open Government Licence v1.0."

Narrative Documents

RD Instruments- Ocean Surveyor 75kHz Vessel mounted ADCP.

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

• Velocity long-term accuracy (typical): ±1.0%, ±0.5cm/s
• Velocity range: -5 to 9m/s
• # of depth cells: 1 - 128
• Max ping rate: 0.7

Bottom Track

Maximum altitude (precision <2cm/s): 950m

Echo Intensity Profile

Dynamic range: 80dB
Precision: ±1.5dB

Transducer and 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)

• Range: -5° to 45°C
• Precision: ±0.1°C
• Resolution: 0.03°

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 on the manufacturer's website or in the specification sheet

RAPID D279 75kHz VMADCP processing

Configuration

The adcp is mounted 0.75m to starboard of the keel and 28.85m aft of the bow. Due to the positioning, this adcp is prone to bubble contamination when the ship is pitching and therefore depth coverage and quality deteriorates noticeably in rough seas.

Data were logged on a PC using RDI data acquisition software (version 1.3). The 75kHz ADCP was configured to sample over 120 second intervals, with 60 bins of 16m thickness, and a blank beyond transmit of 8m. Data were then averaged into 2 minute files. The software logs the PC clock time and its offset from GPS time. This offset was applied to the data during processing, before merging with navigation. Gyro heading and GPS Ashtech heading, location and time were fed as NMEA messages into the software, which was configured to use the gyro heading for coordinate transformation.

Data Originator's Processing

• Data acquisition

  Data were logged on the OS75 PC and transferred by ftp to a UNIX workstation for processing. The following scripts were then run:

  • surexec0: read data into PSTAR format from RDI binary format; write water track data into files of the form sur277nn.raw and equivalent, where nn is a two character code; write bottom track data where present into files of the form sbt277mm; scale velocities to cm/s and amplitude by 0.45 to dB; correct time variable by combining GPS and the PC times; set the depth of each bin.

  • surexec0b: creates daily files.

  • surexec1: edit data(status flag equal to 1 is bad data); edit on percent good variable; move ensemble time to the end of its interval.

  • surexec2: merge data with Ashtech-gyro difference file and correct heading.

  • surexec3: calibrate velocities by scaling by factor A and rotating by angle phi.

  • surexec4: calculate absolute velocities by merging with navigation data (bestnav) and removing the ship's velocity over ground from the ADP data.

• Calibration

  Calibration was undertaken using the following procedure:

  • run through the normal processing steps as described above, with A=1 and phi=0 in surexec3
  • convert bottomew/bottomns into speed and direction
  • convert ve/vn into speed and direction
  • calculate A (=shipspd/botspd) and phi (=shipdirn-botdirn)
  • select a valid subset of data and calculate mean A and phi

  The calibration of the instrument relies on the collection of bottom track data, where the velocity of the bottom relative to the ship can be measured in water depths less than 1000m. This reduces the amount of data collected in the rest of the water column and therefore increases the noise in the measurements. Consequently, the instrument is swapped into bottom tracking mode only when appropriate.

  The data were calibrated using all the available data from D277 and the data from D279. Calculation of the mean A and phi from spot values was undertaken by choosing good input data by visual inspection of the values. Two extra values were calculated: the minimum range (from each of the four transducers) to the bottom and the absolute difference of the minimum and maximum ranges. Records of data were included in the averaging if they occurred in a consecutive sequence of records, which involved stable heading, Ashtech correction and ship's speed, and if the range difference was less than 15m. The data were plotted and outliers removed and A and phi values averaged. The resulting calibration values were: A = 1.004 and phi = -60.12 with standard deviations 0.007 and 0.44 respectively.

BODC post-processing and screening

• Reformatting

  The data were converted from P* format into BODC internal format (QXF) to allow use of in-house visualisation tools. One channel was not taken through the reformatting stage. The originator's identifier for this channel was "good3bm".

• Parameter codes

  All variables were assigned a BODC 8-character parameter code. This code gives information about the variable, for example the method of acquisition and the units of the data.

• Screening

  Reformatted data were visually checked using the in-house editor EDSERPLO. No data values were edited or deleted. Flagging was achieved by modification of the associated quality control flag to 'M' for suspect values and 'N' for nulls.

• Banking

  Once quality control screening was complete, the data were archived in the BODC National Oceanographic Database and the associated metadata were loaded into an ORACLE Relational Database Management System.

Project Information

No Project Information held for the Series

Data Activity or Cruise Information

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

24.5 degrees N Hydrographic Transatlantic section - A05

The hydrographic transatlantic section at 24.5 degrees North has been occupied 8 times, namely in 1957, 1981, 1992, 1998, 2004, 2010, 2015 and 2020. The section is an attempt to calculate the transports of water and its constituents (heat, salinity, nutrients, biological productivity) along this latitude, and to compare the data so that the degree of change in the North Atlantic transports can be revealed. The Hydrographic Programme of the international World Ocean Circulation Experiment (WOCE) designated this section as A05. Since WOCE, the section occupations contribute to the Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP).

Map of stations

The station positions for most of the occupied sections are shown in the above figures. Sections occupied in 1957, 1981, 1992, 1998 and 2004 are shown in the upper figure. The section occupied in 2010 is shown in the lower figure.

The 1957 and 1992 sections each went zonally along 24.5 degrees N from the African coast to the Bahama Islands. Because of diplomatic clearance issues, the 1981, 1998, 2004, 2010 and 2015 sections angled southwestward from the African coast at about 28 degrees N to join the 24.5 degrees N section at about 23 degrees W. The 1998, 2004 and 2010 sections angled northwestward at about 73 degrees W to finish the section along 26.5 degrees N. The 2010 and 2020 sections deviated from the previous sections across the Mid-Atlantic Ridge (MAR) in order to sample the deepest channel and capture the passage of the deep water across the MAR.

Table 1: Occupations of the section

References

Baringer, M. O. N. and R. L. Molinari, 1999. Atlantic Ocean baroclinic heat flux at 24 to 26°N. Geophysical Research Letters, 26, 353-356.

Bryden, H. L., H. R. Longworth, and S. Cunningham, 2005b. Slowing of the Atlantic meridional overturning circulation at 25°N. Nature, 438, 655-657.

Fuglister, F. C., 1960. Atlantic Ocean Atlas of Temperature and Salinity Profiles and Data from the International Geophysical Year of 1957-1958. Vol. 1, Woods Hole Oceanographic Institution Atlas Series, WHOI, Woods Hole, Massachusetts.

King, B. A. et al., 2012. RRS Discovery Cruise 346, 05 Jan-19 Feb 2010. The 2010 transatlantic hydrography section at 24.5N. Southampton, UK, National Oceanography Centre Southampton, 177pp. (National Oceanography Centre Cruise Report, No. 16).

King, B. A. et al., 2016. RRS Discovery Cruise DY040 (RAGNARoCC), 06 Dec 2015 - 22 Jan 2016. The 2015 transatlantic hydrography section at 24.5N. Southampton, UK, National Oceanography Centre Southampton, 159pp. (National Oceanography Centre Cruise Report).

Parilla, G., A.Lavin, H. Bryden, M. Garcia, and R. Millard, 1994. Rising temperatures in the subtropical North Atlantic Ocean over the past 35 years. Nature, 369, 48-51.

Roemmich, D. and C. Wunsch, 1985. Two transatlantic sections: meridional circulation and heat flux in the subtropical North Atlantic Ocean. Deep Sea Research, 32, 619-664.

Sanchez-Franks, A., 2020. RRS James Cook Cruise JC191, 19 January - 1 March 2020. Hydrographic sections from the Florida Straits to the Canaries Current across 24N in the Atlantic Ocean. Southampton, UK, National Oceanography Centre Southampton, 262pp. (National Oceanography Centre Cruise Report, No. 70).

Related Fixed Station activities are detailed in Appendix 1

BODC Quality Control Flags

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

SeaDataNet Quality Control Flags

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

Appendix 1: 24.5 degrees N Hydrographic Transatlantic section - A05

Related series for this Fixed Station are presented in the table below. Further information can be found by following the appropriate links.

If you are interested in these series, please be aware we offer a multiple file download service. Should your credentials be insufficient for automatic download, the service also offers a referral to our Enquiries Officer who may be able to negotiate access.