The CEAREX bathymetry data include trackline data and gridded data.
Information in this document has been derived from documentation files on NSIDC's CD-ROM titled Eastern Arctic Ice, Ocean and Atmosphere Data, Volume 1: CEAREX-1, version 1.0, 8/91.
Bathymetry tracklines on the CEAREX CD-ROM are from three sources:
The digital bathymetry data file consists of both bottom bathymetry and continental topography data for the region of Fram Strait and for a portion of the Arctic Ocean. Specifically, the digital bathymetry data covers a region between 74 degrees north and 88 degrees north over the centrally deep regions of Fram Strait and the Arctic Ocean as well as the East Greenland continental shelf; it covers a region 1650 km by 1650 km with data values every 10 km in both the horizontal and vertical directions. Within the Arctic Ocean, the zonal extent is 60 degrees west to 60 degrees east. The data includes only the fringes of the Barents Sea that border the deeper regions. Surface topography is also included for some realism but should not be relied on.
The bathymetry includes Fram Strait topography on a 10 m by 10 m grid that covers an area extending roughly from 73 degrees north to 90 degrees north and from 60 degrees west to 60 degrees east. Latitude and longitude are given in decimal degrees.
A 12 kHz EDO transducer, a GIFFT transceiver and an oscilloscope were used to periodically measure the depth of the water column at the Oceanography Camp (O-Camp). A mean sound speed of 1492 m/s is assumed in order to convert the travel time of the acoustic signal (echo) to depth. Camp navigation is interpolated from approximately hourly satellite fixes.
The digital bathymetry was created by melding three different data sets, incorporating data for a given region based on the following priority:
The investigators provided the data to the Naval Research Laboratory. The Naval Research Laboratory formatted the data for submission to the marine geophysical data base maintained by the NOAA National Geophysical Data Center (NGDC) Marine Geology and Geophysics Division (MGG). MGG ingested the trackline data and provided files in MGD77 format for the CEAREX CD-ROM.
The scattered data were converted from latitude/longitude to an X-Y Cartesian system using a Lambert's Conic Conformal transformation, gridded using a minimum tension algorithm, and then contoured to check for accuracy. If specific regions were not modeled accurately enough, additional data were employed and the process was repeated.
Since the 1983 bathymetry did not show the Belgica Bank and its associated troughs located on the northeast Greenland Shelf (Bourke et al. 1987), the resulting bathymetry was graphically edited to include this feature for completeness. The graphical editing of the bathymetry within the region of the Belgica Bank is by its very nature not exact, but provides a fair degree of realism. Separate files do exist for the continental coastlines of Greenland, Svalbard, and many of the smaller islands.
The bathymetry trackline data and digital bathymetry data are presented in separate subdirectories on the CEAREX CD-ROM. The bathymetry trackline data are presented in six ASCII data files, and the digital bathymetry data are presented in a single data file.
Because no other "standard" format was available, the Marine Geophysical Data Exchange Format (MGD77) was used to present the tracklines. The user community is invited to comment on the utility of this format for data analysis. It appears that a gridded format may be more useful; as the set of available tracklines for the Eastern Arctic grows, the feasibility of gridding the data for inclusion on possible future CD-ROM's will be investigated.
The description of the MGD77 format in this document is extracted from MGD77 Task Group (1989), which is available on request from:
NOAA/National Geophysical Data Center, 325 Broadway, Boulder, CO 80303 USA
MGD77 uses 16 header records composed of 80-character "sequences" to describe the data. A sequence is a logical record that ends with its sequence number in positions 79-80. The 120-character physical records are composed of 1.5 sequences each. The header sequences are defined in a header record table in the CD-ROM documentation file. Data records are 120-character records with contents and format described in a data record table in the CD-ROM documentation file. To use the data in a program, read consecutive strings of 80 characters in the order described in the tables.
Data are presented in 54-character ASCII records containing five columns, one each for latitude, longitude, Z, X and Y, where:
Z is elevation in meters, 0 being sea level
if Z is less than 0 => bottom bathymetry,
if Z is greater than 0 => continental topography (crude)
X (km) is the resulting transform of the latitude and longitude pair using Lambert Conic Conformal (LCC) mapping
Y (km) is the resulting transform of the latitude and longitude pair using LCC mapping
The Lambert transformation used a latitude-longitude origin of 74degrees north and 25 degrees west, a central meridian of 0 degrees, a central parallel of 79 degrees north, minimum and maximum parallels of 76 degrees north and 82 degrees north and a scale factor of 1:10000. A conversion factor of 0.25423619 was used to convert LCC output to true distance in kilometers determined from great circle distance.
The first twelve records in the file are shown here as sample data. The first and second records are informative headers.
Filename: \BATHY\MANLEY.BTH Latitude Longitude Z Y X 73.0026 -25.1198 14 -100 -50 73.0396 -24.8420 -21 -100 -40 73.0763 -24.5631 -20 -100 -30 73.1125 -24.2829 -11 -100 -20 73.1484 -24.0016 -5 -100 -10 73.1839 -23.7191 0 -100 0 73.2190 -23.4354 11 -100 10 73.2537 -23.1505 -49 -100 20 73.2880 -22.8644 -68 -100 30 73.3218 -22.5772 -29 -100 40
The header for the file ACAMP.BTH was added at NSIDC and may contain more information after it has been ingested by MGG.
The file \BATHY\OCAMP.BTH, contains data from the O-Camp provided by D. Menemenlis of the Institute of Ocean Sciences, Sidney, British Columbia. These data were intended for inclusion in the MGD77 format files; however, it is not certain that they were actually included. To ensure their availability, the data are provided separately in a file containing descriptive text and in a text file in the CD-ROM documentation file. These data will be incorporated into the bathymetry data set on the next version or volume of the Eastern Arctic CD-ROM series. NSIDC apologizes for any inconvenience this may cause.
The surface topography data should not be relied on.
As of December 1990, there were many useful maps but no acceptable digital data of bottom bathymetry in the region of Fram Strait. For example, DBDB5 omitted or poorly represented the Molloy Deep. In an attempt to address this problem until such time as sufficient observations in the Arctic are obtained to provide a complete, high-resolution digital bathymetry, Thomas Manley created the digital data presented on the CEAREX CD-ROM early in 1990 for his own research purposes.
Arthur B. Baggeroer, Massachusetts Institute of Technology - acoustics camp
Norman Z. Cherkis, Naval Research Laboratory - data collection, ingest
Dimitris Menemenlis, Institute of Ocean Sciences - oceanography camp
Keith von der Heydt, Woods Hole Oceanographic Institution - acoustics camp
A.M. Hittelman, NOAA, National Geophysical Data Center - MGD77 format
Thomas O. Manley, Marine Research Corporation
For a complete list of all CEAREX investigators, please refer to the CEAREX Investigator Address List.
MGD77 Task Group 1989. Key to Geophysical Records Documentation no. 10 (revised): Marine Geophysical Data Exchange Format - 'MGD77' (Bathymetry, Magnetics, and Gravity). NOAA, National Geophysical Data Center, 16 p.
ASCII - American Standard for Computer Information Interchange
CD-ROM - Compact Disc-Read Only Memory
CEAREX - Coordinated Eastern Arctic Experiment
DBDB5 - not defined
EDO - not defined
GIFFT - not defined
kHz - kilohertz
LCC - Lambert Conic Conformal
MGG - Marine Geology and Geophysics Division
NGDC - National Geophysical Data Center
NOAA - National Oceanic and Atmospheric Administration
NSIDC - National Snow and Ice Data Center