AWI Bathymetric Chart of the Fram Strait (BCFS)
Based on data from R/V Polarstern multibeam sonar surveys between 1984 and 1997 we produced a high resolution bathymetry of the central Fram Strait. The area insonified covers approx. 36,500 km² between 78°N - 80°N and 0°E - 7.5°E. Basic outcome of the investigation is a raster Digital Terrain Model (DTM) with 100 m grid spacing which was utilized for contouring and generation of a new series of bathymetric charts, the AWI Bathymetric Charts of the Fram Strait (AWI BCFS) at a scale of 1:100,000.
Up to present only coarse bathymetric information existed in the region due to the remote location and annual ice-cover, making systematic surveys logistically demanding.
Animation:
Cruise around Molloy Hole Data source: RV Polarstern multibeam data; 3x height exaggeration; Fram Strait; File size: 5.2 MB. The Digital Terrain Models were animated using the IVS Fledermaus software.More information:
- A short note on Fram Strait feature names
- Regional setting and relevance for local and global climate trends
- Data issues: data sources, R/V Polarstern tracklines, etc.
- Data processing
- Description of the Fram Strait bathymetry
- Data products and downloads
- References & acknowledgements
Fram Strait data sources
The Fram Strait has been frequently visited by R/V Polarstern during recent decades. Multibeam bathymetry data from nine cruises have been evaluated for the generation of a Digital Terrain Model (DTM). The total measure time of the multibeam systems adds up to 47 days. More than 10 million single depth values had to be processed.
Track lines of nine Polarstern cruises, where data were derived for the Bathymetric Chart of the Fram Strait.
Cruises and data acquisition dates
| CRUISE | YEAR | MEASURE TIME | ECHOSOUNDER |
| ARK-I/4 | 1984 | 6 days | Seabeam |
| ARK-III/2 | 1985 | 2 days | Seabeam |
| ARK-III/3 | 1985 | 7 days | Seabeam |
| ARK-IV/1 | 1987 | 3 days | Seabeam |
| ARK-IV/3 | 1987 | 6 days | Seabeam |
| ARK-VII/3a | 1990 | 10 days | Hydrosweep DS-1 |
| ARK-VIII/3 | 1991 | 5 days | Hydrosweep DS-1 |
| ARK-XI/2 | 1995 | 5 days | Hydrosweep DS-1 |
| ARK-XIII/3 | 1997 | 3 days | Hydrosweep DS-1 |
Multibeam systems
Two multibeam systems have been in use. From ARK-II/4 to ARK-IV/3 the Seabeam system provided 16 depth values across-track per ping. In 1989 the Seabaem aperture was superseded by the Hydrosweep DS-1 multibeam echosounder providing 59 individual across-track soundings per ping. The Hydrosweep system also provides a wider fan of across-track insonification thus enhancing the survey area per unit time.
Further technical characteristics are shown in the table. Point spacings at 2500 m water depth are approximate values for an idealized flat horizontal sea bottom. The point density and spatial distribution has to be taken into account when choosing a gridding method and grid spacing for DTM interpolation.
| SEABEAM | HYDROSWEEP | |
| Introduction | 1982 | 1989 |
| Frequency | 12.3 kHz | 15.5 kHz |
| No. of beams | 16 | 59 |
| Fan width | 42.67° | 90° (120°) |
| Beam width | 2.67° | 2.3° |
| Track width (x nadir depth) | 0.73 | 2.0 (90°) |
| Point spacing across track at 2500 m depth | approx. 131 m (center beams), approx. 151 m (outer beams) | approx. 67 m (center beams), approx. 130 m (outer beams) |
| Point spacing along track at 2500 m depth | approx. 25 m | approx. 50 m |
When mosaicking and merging data from different cruises the navigation quality is of prime importance. Navigation systems onboard R/V Polarstern have changed over the years starting with Indas/Transit via GPS-based ANP/Kompass to a NACOS DGPS system. Navigation accuracy in the study area has correspondingly improved since the early eighties from the range of kilometres to metres (worst case scenarios).
Since navigation fixes were sparse during the earlier cruises which used Transit, particulary in high latitudes, actual positional data during surveys had to be calculated from one fix to another using vessel speed/heading information - a process called dead reckoning. Until the introduction of two redundant MINS laser systems, the mechanical gyros that had been used as motion sensors were a prevalent source of error, particularly after narrow turns that are characteristic of systematic surveying, as they needed a considerable time for retuning.