Abstract:
This dataset comprises of vertical aerial imagery of sea ice in Marguerite Bay and Crystal Sound in 2015, the point locations of ice seals detected in that imagery, and polygons denoting the area of the surveys. It was done initially to test the possibility of counting ice seals in aerial and satellite imagery and will be used in future as a baseline dataset to track ice seal abundance in the region. The points were manually digitised in ArcGIS by one observer.
The original imagery was taken by operators from the BAS Mapping And Geographic Information Centre. Counting and analysis was part of the NERC grant NE/W009641/1.
Keywords:
Ice seals, Lobodon carcinophagus, aerial survey, crabeater seals, population density, sea ice
Fretwell, P.T., & Ireland, L. (2025). Imagery and crabeater seal point locations from aerial surveys of Crystal Sound and Marguerite Bay, West Antarctic Peninsula 2015 (Version 1.0) [Data set]. NERC EDS UK Polar Data Centre. https://doi.org/10.5285/8262f384-88e7-4dad-89f5-45687b4e2d5a
| Access Constraints: | None. |
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| Use Constraints: | This data is governed by the NERC data policy http://www.nerc.ac.uk/research/sites/data/policy/ and supplied under Open Government Licence v.3 http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/. |
| Creation Date: | 2025-08-28 |
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| Dataset Progress: | Complete |
| Dataset Language: | English |
| ISO Topic Categories: |
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| Parameters: |
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| Personnel: | |
| Name | UK Polar Data Centre |
| Role(s) | Metadata Author |
| Organisation | British Antarctic Survey |
| Name | Dr Peter T Fretwell |
| Role(s) | Investigator, Technical Contact |
| Organisation | British Antarctic Survey |
| Name | Ms Louise Ireland |
| Role(s) | Investigator |
| Organisation | British Antarctic Survey |
| Parent Dataset: | N/A |
| Reference: | Associated paper: C. McGinnity, C.C.G. Bamford, N. Fenney, A. Fleming, J. Forcada, M.S. Tift, L.A. Hückstädt, D.P. Costa, P.T. Fretwell (2025) Semi-Automated Seal Detection on the Western Antarctic Peninsula: An Unsupervised Machine Learning Approach for Detecting Ice Seals in Aerial Survey Data [Preprint]. Remote Sensing in Ecology and Conservation. https://doi.org/10.1101/2025.08.22.671691 |
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| Quality: | Spatial resolution of the imagery is 12cm per pixel Ground Sample Distance (GSD). Seal locations have been marked, but species cannot be differentiated. No accuracy metrics are included. Horizontal datum: EPSG:3031 - WGS84 Antarctic Polar Stereographic Vertical datum: MSL (mean sea level) |
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| Lineage/Methodology: | Between 31 October and 10 November 2015, British Antarctic Survey flew three lines of aerial survey over sea ice adjacent to the Antarctic Peninsula to survey pack ice seals. Image coverage of Maguerite Bay was taken twice; once on 31 October, and once on 10 November, to assess the variability of seal presence. A separate line was flown over Crystal Sound on 8 November. A Twin Otter aircraft was mounted with a vertical facing high resolution Z/I Imaging Digital Mapping Camera (DMC) and, flying at a height of 1200m, around 1600km of imagery was acquired of the pack ice with an on-the-ground resolution of 12cm per pixel. Images were taken approximately every 700m and had a 40% overlap. Each image was post processed using the IMU (inertial measurement unit) data from the aircraft that gives position and orientation to enable georectification of each photograph. In the resulting imagery seals can be clearly seen, often with pups and recent tracks. These seals were manually digitised with a single point placed on each seal in ArcGIS (version 10.4 ESRI 2025). Searching was done systematically at 1:800 scale, where images overlapped, only the seals from the first image viewed was recorded. The resulting point shapefiles record all seals in the three flightlines. |
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| Temporal Coverage: | |
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| Start Date | 2015-10-31 |
| End Date | 2015-11-10 |
| Spatial Coverage: | |
| Latitude | |
| Southernmost | -66.54 |
| Northernmost | -66.29 |
| Longitude | |
| Westernmost | -66.84 |
| Easternmost | -66.44 |
| Altitude | |
| Min Altitude | N/A |
| Max Altitude | N/A |
| Depth | |
| Min Depth | N/A |
| Max Depth | N/A |
| Latitude | |
| Southernmost | -68.6 |
| Northernmost | -67.83 |
| Longitude | |
| Westernmost | -68.72 |
| Easternmost | -68.67 |
| Altitude | |
| Min Altitude | N/A |
| Max Altitude | N/A |
| Depth | |
| Min Depth | N/A |
| Max Depth | N/A |
| Data Resolution: | |
| Latitude Resolution | N/A |
| Longitude Resolution | N/A |
| Horizontal Resolution Range | < 1 meter |
| Vertical Resolution | N/A |
| Vertical Resolution Range | N/A |
| Temporal Resolution | N/A |
| Temporal Resolution Range | N/A |
| Location: | |
| Location | Antarctica |
| Detailed Location | Marguerite Bay, Western Antarctic Peninsula |
| Location | Antarctica |
| Detailed Location | Crystal Sound, Western Antarctic Peninsula |
| Sensor(s): |
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| Source(s): |
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| Data Collection: | Imagery was acquired using Intergraph's Z/I Imaging Digital Mapping Camera (DMC). Points were digitised in ArcGIS version 10.4 Trimble Applanix software was used to create the camera centre points from the onboard IMU data. SOCET GXP was used to undertake the areo-triangularization and georectification of the images. |
| Distribution: | |
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| Distribution Media | Online Internet (HTTP) |
| Distribution Size | 428 KB |
| Distribution Format | ASCII |
| Fees | N/A |
| Distribution Media | Online Internet (HTTP) |
| Distribution Size | 16 GB |
| Distribution Format | TIFF |
| Fees | N/A |
| Data Storage: | annotation_layers folder containing 428KB of shapefiles: 3 x GIS shapefiles containing point data and relevant information on the photocentres in the database, two of Marguerite Bay (both surveys) and one of Crystal Sound. Named: marguerite_bay_1_photo_centres.shp marguerite_bay_2_photo_centres.shp crystal_sound_photo_centres.shp Description of the attribute table columns for the photo centres: photo_id : aerial photograph filename. time: number of seconds from midnight in GPS time. lat : latitude in decimal degrees. long : longitude in decimal degrees. emg96_z : the geoidal adjustment (z) at the photo centre taken from the egm96 geoid in cm. sortie : unique identifier of the BAS aerial survey sortie. date_flown : the date the sortie was flown in YYYY-MM-DD fornat. 3 x GIS shapefiles containing point data of seals manually digitised from the aerial imagery. Named: crystal_sound_sealcount.shp marguerite_bay_1_A10_sealcount.shp marguerite_bay_2_A23_sealcount.shp 2 x GIS shapefiles each containing a single polygon showing the areas covered in the Crystal Bay and Marguerite Bay surveys. Named: crystal_sound_coverage.shp marguerite_bay_coverage.shp imagery folder containing 16GB of tif files: 3 x folders of vertical aerial photos used in the survey, in .tif format. Named: crystal_sound_20251108 - 59 photos, numbers BAS201603C_032_049 to 107 marguerite_bay_1_20251031 - 118 photos, numbers BAS201602B_A10_001 to 118 marguerite_bay_2_20251110 - 115 photos, numbers BAS201604C_A23_81 to 195 Please note that the photograph folder and file names refer to the year the photos were processed, not the year they were taken. |