Metadata Report for BODC Series Reference Number 1725883

• 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

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

Instrument Description

The LADCP data were collected using the instrumentation detailed below:

The LADCP system consisted of one Teledyne RDI Workhorse 300kHz ADCP, a battery and interconnection cables mounted on the CTD rosette, pointing downwards.

The instrument configurations for all except the towyo stations were as follows; 25 x 8m bins, zero blanking distance, narrow bandwidth, 4.0 ambiguity velocity, 1.3s/1.5s staggered ping rate. This is one of the configurations that was used during the DIMES UK2 cruise (JC054). For the towyo stations, in order to reduce the battery consumption, the staggered ping rate was changed to 1.8s/2.0s.

Teledyne RDI's Workhorse Monitor ADCP

The Workhorse Monitor acoustic doppler current profler (Teledyne RD Instruments) is a long-range and long-term self contained ADCP. It has a patented four beam signal (300, 600 or 1200 kHz) and a standard depth rating of 200m or 600m. It operates effectively between temperatures of -5°C and 45°C and has a velocity accuracy of ±1% ±5mm/s.

BODC Processing

LDEO processed data were provided by the originator in Matlab and ASCII formats. The LDEO processed data in ASCII format were converted into BODC internal format after discussion with the originator. The following table shows how the variables within the ASCII files were mapped to appropriate BODC parameter codes:

All reformatted data were visualised using the in-house Edserplo software. Suspect and missing data were marked by adding an appropriate quality control flag.

Note that the more complex LDEO processed data are available on request in Matlab format as well as the unprocessed raw LADCP files.

Originator's Data Processing

Sampling Strategy

LADCP profiles were collected at all CTD stations in order to derive full depth profiles of ocean velocity, as well as profiles of finescale vertical shear of horizontal velocities. A total of 95 LADCP profiles were obtained for each of the CTD stations, this included 23 towyo profiles, 40-62 and 76-78.

Data processing

Preliminary shipboard processing of the LADCP data was carried out with the LDEO LADCP processing software Version IX. To obtain high-quality full-depth velocity profiles, bottom-tracking data, GPS data, shipboard-ADCP (SADCP) data, and CTD time-series were used.

CTD time-series with a temporal resolution of 1s with uncalibrated salinty was used. The GPS time series with the same temporal resolution of the CTD time-series was collected and merged with the CTD data for each cast.

During each CTD/LADCP deployment, SADCP data were collected with two separate systems (150 kHz and 75 kHz). For most stations, only data from the 75kHz system were used for LADCP processing. But for stations 13, 85 and 86, the 75kHz SADCP did not function well, therefore data from the 150kHz were used.

Although the ADCP had the RDI LADCP mode (WM15) installed which reported bottom-tracking data calculated from water-tracking pings, from the experience during cruise JC054, post-processed bottom tracking data was used to constrain the velocity measurements. Due to the time limit, at some stations the CTD rosette was only deployed to the depth of tracer, therefore no bottom-tracking data were obtained. For those stations, only the GPS and SADCP were used as constrains. The data quality at those stations is therefore expected to be lower.

It is noted in the cruise report that some LADCP casts did not have bottom tracking. The .log and .txt files were checked to determine which casts did not. Casts 01, 02, 24, 37, 94, 95, 96, 97, 98, 99, 100 and towyo profiles 40, 41 and 44 did not have bottom tracking.

The towyo profiles were processed separately from the standard CTD profiles. The following steps were carried out for those stations (40-62 and 76-78):

1) The raw LADCP data were divided into different casts by finding the ensemble numbers of turn points near the surface based upon variations of vertical velocities, temperatures and tilts.

2) The depth in the CTD time-series files were modified by subtracting the start depth from all depth values.

3) The section of SADCP data between the start depth of CTD cast and surface were removed. The depth of SADCP file was modified in the same way dealing with CTD data.

4) The files were then processed along with the other standard profiles. After running the LDEO LADCP software, the depths in the output files were modified by adding the values that were subtracted in the second step.

Please refer to Thurnherr (2014) for a more detailed LADCP processing methodology.

References

How To Process LADCP Data With the LDEO Software, Versions IX.7 to IX.10.

Project Information

Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) project document

DIMES is a US/UK field program aimed at measuring diapycnal and isopycnal mixing in the Southern Ocean, along the tilting isopycnals of the Antarctic Circumpolar Current.

The Meridional Overturning Circulation (MOC) of the ocean is a critical regulator of the Earth's climate processes. Climate models are highly sensitive to the representation of mixing processes in the southern limb of the MOC, within the Southern Ocean, although the lack of extensive in situ observations of Southern Ocean mixing processes has made evaluation of mixing somewhat difficult. Theories and models of the Southern Ocean circulation have been built on the premise of adiabatic flow in the ocean interior, with diabatic processes confined to the upper-ocean mixed layer. Interior diapycnal mixing has often been assumed to be small, but a few recent studies have suggested that diapycnal mixing might be large in some locations, particularly over rough bathymetry. Depending on its extent, this interior diapycnal mixing could significantly affect the overall energetics and property balances for the Southern Ocean and in turn for the global ocean. The goals of DIMES are to obtain measurements that will help us quantify both along-isopycnal eddy-driven mixing and cross-isopycnal interior mixing.

DIMES includes tracer release, isopycnal following RAFOS floats, microstructure measurements, shearmeter floats, EM-APEX floats, a mooring array in Drake Passage, hydrographic observations, inverse modeling, and analysis of altimetry and numerical model output.

DIMES is sponsored by the National Science Foundation (U.S.), Natural Environment Research Council (U.K) and British Antarctic Survey (U.K.)

For more information please see the official project website at DIMES

Data Activity or Cruise Information

Cruise

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:

SeaDataNet Quality Control Flags

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