DOI: 10.5285/386eef1f-2dc7-413c-8ff4-c90722c047f4
title: Topographic contours of Signy Island (March 2015)

description: Topographic contours of Signy Island with 10 m intervals, derived from a digital elevation model originally created using stereoscopic photogrammetry from VHR (very high resolution) In-Track stereo satellite imagery collected during March 2015.
The topographic contours were created to support the updated release of the British Antarctic Survey (BAS) Signy Island map (BAS, 2024).
The dataset is available as a polyline shapefile and a GeoPackage.
WorldView-3 satellite images © 2015 Maxar Technologies.
description: Photogrammetry and terrain extraction:
The stereo VHR satellite images were processed in Socet GXP. Image triangulation was undertaken using a combination of known ground control points and automatically generated tie points. Following image triangulation, a digital elevation model was extracted using an automatic terrain extraction algorithm. The resulting digital elevation model was then compared with the original imagery using a stereoscopic monitor. Where the digital elevation model deviated from the imagery, these deviations were corrected manually. The digital elevation model was then exported from Socet GXP as a georeferenced .tif file.
WorldView-3 satellite images © 2015 Maxar Technologies.

Contour extraction:
Contours were extracted from the above digital elevation model using the 'Contour' tool in ArcGIS Pro v3.3.0 with a 10 metre interval. All anomalous contours less than 10 m in elevation were deleted, and any lines with a length less than 10 m were also deleted.

Coordinate reference system:
The projected coordinate system is WGS84 UTM Zone 23S. 

Dataset Fields:
The dataset has an attribute field displaying the contour elevation related to Mean Sea Level (MSL) at Signy Research Station. Signy MSL is defined in the following report, BAS Archive reference no. AD6/2H/2001/L1 'GPS Survey Field Report - 2001-02 Antarctic Field Season', but to summarise: MSL is defined by the tide gauge at Signy Station. To transform data from WGS84 to Signy MSL, apply a local correction factor of -32.235 m (MSL is below WGS84). To access the full field report, please contact British Antarctic Survey Archives service.
description: Source imagery:
In-Track stereo WorldView-3 (MAXAR) VHR (very high resolution) satellite imagery.
WorldView-3 satellite images © 2015 Maxar Technologies.

Photogrammetry software:
Socet GXP (version 4.5.1.5)

GIS software:
ArcGIS Pro (version 3.3.0)
description: Image triangulation during the Socet GXP photogrammetric workflow was undertaken using a combination of ground control points and automatically generated tie points. The ground control points provided a global geospatial reference and were sourced from an earlier GNSS (global navigation satellite system) survey conducted around Signy Island during the 2001/02 Antarctic field season.

Identifying the original ground control points proved challenging due to the limited resolution of the satellite imagery and the duration of time that had passed between the original GNSS survey and the satellite capture. Points that could not be identified or no longer existed were removed.

The average error across the remaining ground control points following image triangulation was around 0.5 m.

Please refer to the original field report for an estimation of accuracy of the individual ground control points. BAS Archive reference no. AD6/2H/2001/L1 'GPS Survey Field Report - 2001-02 Antarctic Field Season'.

Please note, the additional error created as a result of the terrain extraction and contour creation workflows will vary across the dataset and has not been formally calculated but is expected to be around 2 - 3 m.