Metadata Report for BODC Series Reference Number 1030275


Metadata Summary

Data Description

Data Category Bathymetry
Instrument Type
NameCategories
Kongsberg (Simrad) EM 120 multibeam echosounder  multi-beam echosounders
Instrument Mounting research vessel
Originating Country United Kingdom
Originator Mr Peter Hunter
Originating Organization Southampton Oceanography Centre (now National Oceanography Centre, Southampton)
Processing Status banked
Project(s) -
 

Data Identifiers

Originator's Identifier JCR99_MB_REF_GRD
BODC Series Reference 1030275
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 2003-08-21 12:00
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval -
 

Spatial Co-ordinates

Southernmost Latitude 58.81000 N ( 58° 48.6' N )
Northernmost Latitude 59.66000 N ( 59° 39.6' N )
Westernmost Longitude 11.26500 W ( 11° 15.9' W )
Easternmost Longitude 8.98750 W ( 8° 59.3' W )
Positional Uncertainty 0.0 to 0.01 n.miles
Minimum Sensor Depth -
Maximum Sensor Depth -
Minimum Sensor Height -
Maximum Sensor Height -
Sea Floor Depth -
Sensor Distribution -
Sensor Depth Datum -
Sea Floor Depth Datum -
 

Parameters

BODC CODE Rank Units Short Title Title
ALATZZ01 0 Degrees Lat Latitude north
ALONZZ01 0 Degrees Lon Longitude east
ACYCAA01 1 Dimensionless Record_No Sequence number
MBAN1234 2 Metres BathyDepSwathGMT Sea-floor depth (below mean sea level) {bathymetric depth} by multi-beam echo sounder and gridded using Generic Mapping Tools (GMT) software
 

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

Public domain 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.

The recommended acknowledgment is

"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."


Narrative Documents

Kongsberg EM120 Multibeam Echosounder

The EM120 is a low frequency (12 kHz) multibeam echosounder with full ocean depth capability designed for bathymetric surveys. It measures water depth by monitoring the travel time of an acoustic signal that is transmitted from the ship, reflected off the seabed and received back at the ship.

The main system units of the EM120 are transducer arrays (separate for reception and transmission), preamplifier unit, transceiver unit and operator unit. Sub-bottom profiling capability is an optional extra. For both transmit and receive arrays standard beamwidth is 1° or 2°, and 4° beamwidth is available for the receive array.

The system has 191 beams with pointing angles automatically adjusted according to achievable coverage or operator defined limits. The beam spacing is normally equidistant, corresponding to 1% of depth at 90° angular coverage, 2% at 120° and 3% at 140°. The transmit fan is split into several individual sectors, each of which is corrected independently for vessel roll, pitch and yaw, which places all soundings on a "best fit" to a line perpendicular to the survey line.

The EM120 supersedes the EM12 and was itself superseded by the EM122 in 2008.

Specifications

Frequency 12 kHz
Maximum ping rate 5 Hz
Range sampling rate 2 kHz
Swath coverage sector up to 150°
Swath width up to 5.5 x water depth
Depth resolution 10 to 40 cm
Depth range 20 to 11,000 m
Pulse length 2, 5 and 15 ms
Number of beams 191
Beam width

1° x 1°
1° x 2°
2° x 2°
2° x 4°

Beam spacing (at angular coverage)

1% of depth at 90°
2% of depth at 120°
3% of depth at 140°

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

BODC Data Processing

The data were provided to BODC in as Generic Mapping Tools (GMT) output NetCDF .grd format. In addition to this file, BODC were also provided with the raw xyz file, which is available upon request.

The files provided appeared to have been written with an early version of GMT, using a now deprecated grid file format (cf #10). To solve the issue, the each file was converted to ASCII format from the NetCDF .grd file. The ASCII grid file was then converted back to a GMT NetCDF grid using a current version of GMT. The new file was then transferred, using BODC generated Matlab code, into BODC standard NetCDF format.

During transfer the original variables are mapped to unique BODC parameter codes. The parameter mapping can be seen below.

Originator's variable Units Description BODC Parameter Code Units Comments
x Degrees Longitude ALONZZ01 Degrees Eastern values are positive
y Degrees Latitude ALATZZ01 Degrees Northern values are positive
z Metres Sea floor depth MBAN1234 Metres -

During transfer plots of the original files and of the transferred files were produced. These were visually compared to check that the data has transferred correctly. No problems were detected.

Originator's Data Processing

Bathymetry data were collected by a Simrad EM120 multi-beam echo sounder. Details of the sampling and on-board data processing are available in sections 3.1 and 5 of the JR99 cruise report.


Project Information


No Project Information held for the Series

Data Activity or Cruise Information

Cruise

Cruise Name JR20030816 (JR99)
Departure Date 2003-08-16
Arrival Date 2003-08-27
Principal Scientist(s)Carol J Pudsey (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