Further by downloading this data the user acknowledges that they agree with the NERC data policy (), and the following conditions:

1. To cite the data

Abrahamsen, E. P. (2020). Gridded bathymetric compilation of selected areas within the Orkney Passage, Scotia Sea from multibeam echosounder data collected by multiple vessels (1989 - 2017) [Data set]. UK Polar Data Centre, Natural Environment Research Council, UK Research & Innovation. https://doi.org/10.5285/1221BBBD-843E-46D6-B96C-9C559AECFB20

2. The user recognizes the limitations of data and will not use this data for navigation purposes. Use of the data is at the users' own risk, and there is no warranty as to the quality or accuracy of any data, or the fitness of the data for your intended use. The data are not necessarily fully quality assured and cannot be expected to be free from measurement uncertainty, systematic biases, or errors of interpretation or analysis, and may include inaccuracies in error margins quoted with the data.

Methodology:

The bathymetry map was compiled from a variety of different data sources. The primary data are multibeam swath bathymetry collected from scientific cruises undertaken by British Antarctic Survey (BAS), Alfred Wegener Institute (AWI), or acquired during ESPS RV Hesperides expeditions. The complete list of the cruises used for the compilation is the following:

-RV Polarstern: ANT-VIII/5, ANT-XXII/4, ANT-XXIII/7

-RRS James Clark Ross: JR149, JR239, JR252, JR257/272A, JR259, JR281, JR310, JR16005

-ESPS RV Hesperides: hes97

The first grid (m41_swath_50m_nc.grd) was created using the mbgrid program from MB-system version 5.5.2336 , using the parameters "-E50/50/meters -R-39.6/-39.1/-60.7/-60.55 -G3 -A2 -T25 -W4 -M -N -C5/1 -P1 -F1 -V". This uses a Gaussian weighted mean filter. Values are interpolated using a spline (tension 25) up to five grid cells from the nearest data point only if additional data are found in two opposite directions.

The second grid (m42-44_swath_50m_nc.grd) was created using the mbgrid program from MB-system version 5.5.2336, using the parameters "-E50/50/meters -R-42.6/-41.7/-60.8/-60.45 -G3 -A2 -T25 -W4 -M -N -C5/1 -P1 -F1 -V". Like the first grid, this uses a Gaussian weighted mean filter. Values are interpolated using a spline (tension 25) up to five grid cells from the nearest data point only if additional data are found in two opposite directions.

Data quality:

Quality control was undertaken manually to remove any outliers in the source datasets. This involved cleaning much of the raw data using the "mbedit" program from MB-system. For data processed in this way, edit files have been submitted to the Polar Data Centre. In source files that were ingested as text files, outliers were manually removed.

To verify the accuracy of the resulting dataset, bottom depths were compared against CTD casts on cruise JR16005, excluding casts that were performed when the ship was moving and those where the CTD did not get within altimeter range of the bottom. Bottom depths were calculated from the CTD altimeter when near the bottom, and these were compared against the gridded dataset. On 81 casts, the median difference between the CTD-derived depths and gridded depths was 4.1 m with a standard deviation of 18.9 m. This compares favourably with GEBCO_2014, which had a median offset of 4.6 m with a standard deviation of 73.4 m, and GEBCO_2019, which has a median offset of 0.5 m but a standard deviation of 89.4 m.