Depth of the sea floor along the 5-minute resolution cruise track of the Antarctic Circumnavigation Expedition (ACE) derived from GEBCO 2019 bathymetry data.

***** Dataset abstract *****

Depth of the seabed along the five-minute averaged cruise track (Landwehr et al., 2020; DOI: 10.5281/zenodo.3752691) of the Antarctic Circumnavigation Expedition (ACE) was calculated from the the General Bathyemtric Chart of the Oceans (GEBCO; GEBCO Compilation Group, 2019) 2019 gridded 30-arc second bathymetry data. The nearest gridded value from the bathymetry dataset was used to find the depth at the averaged position. 

Provided within this dataset is the average position of the vessel during a five-minute time period (where the time given is the middle time of the averaging interval).

***** Original data collection *****

GeoTIFF files of gridded bathymetry data from the GEBCO grid (GEBCO Compliation Group, 2019) were used to obtain values of sea floor depth. The bathymetry dataset provided gridded values of sea floor depth with a grid size of 30 arc-seconds which is equivalent to a resolution of approximately 2.83 times the grid size (NOAA National Centers of Environmental Information, https://www.ngdc.noaa.gov/mgg/topo/report/s6/s6A.html). Grid size varies in both the east-west and north-south directions, with latitude. The bounding boxes of the GEBCO data used were 180 W to 180 E and 30 S to 90 S, as well as 30 W to 30 E and 30 S to 60 N.

A five-minute averaged cruise track of ACE provided the positions of the vessel (Landwehr et al., 2020; DOI: 10.5281/zenodo.3752691).

***** Data processing *****

All GeoTIFF files containing the bathymetry data were merged into one file using the package rasterio (Rasterio, MapBox, 2016). Comma-separated values (CSV) files were converted to GeoJSON features with date_time as a property, using the python package geojson. These GeoJSON features then underwent analysis with the rasterstats package (Rasterstats, Perry, 2015) using the function gen_point_query which gets a depth value for each point location. Finally, these values are written out to a CSV file.

This processing was done using the python code in the file get_gebco_depth_along_track.py (part of science-data-utils0.4.0; DOI 10.5281/zenodo.3746110) and run using Python version 3.7.3 inside a virtual environment in Renkulab (https://renkulab.io usin Renku version 0.6.1). Versions of python packages that were used are as follows:
affine==2.3.0
attrs==19.3.0
click==7.1.1
click-plugins==1.1.1
cligj==0.5.0
Fiona==1.8.13.post1
geojson==2.5.0
munch==2.5.0
numpy==1.18.2
pyparsing==2.4.7
rasterio==1.1.3
rasterstats==0.14.0
Shapely==1.7.0
simplejson==3.17.0
six==1.14.0
snuggs==1.4.7
termcolor==1.1.0

***** Quality checking *****

No further processing of the data has been done to ensure that positions where depth appears to show the ship on land (i.e. depth > 0 m) has been done. 

***** Standards *****
 
This dataset conforms to parameter naming conventions using CF standard names. 

***** Further information for interpreting the data and using the dataset *****

Timescales: timescales are not relevant for the depth in this dataset. 

Interpolation: depth values can be interpolated. See the original cruise track dataset for information about interpolation of positions.

Aggregation to lower temporal resolution: the latitude of the vessel should be taken into consideration. Moving at 12 knots, the vessel could cover two or more of the grid squares for which the bathymetry data are provided. Aggregating the data to a lower resolution could mean that positions and depths are resolved that mean the vessel would be "placed" on land as it passed near to the coast and many islands during the voyage.

***** Dataset contents *****

- cruise_track_gebco2019_depth_5min, data file, comma-separated values
- data_file_header.txt, metadata, text
- README.txt, metadata, text

***** Dataset contact *****

Jenny Thomas, Swiss Polar Institute, Switzerland. ORCID: 0000-0002-5986-7026. Email: jenny.thomas@epfl.ch; jtsciencedata@gmail.com

***** Dataset license *****

This GEBCO sea floor depth along the cruise track dataset from ACE is made available under the Creative Commons Attribution 4.0 International License (CC BY 4.0) whose full text can be found at https://creativecommons.org/licenses/by/4.0/

***** Dataset citation *****

Please cite this dataset as:
Thomas, J., Pina Estany, C. and Landwehr, S. (2020). Depth of the sea floor along the 5-minute resolution cruise track of the Antarctic Circumnavigation Expedition (ACE) derived from GEBCO 2019 bathymetry data. (Version 1.0) [Data set]. Zenodo.