Turks and Caicos Islands

Figure 4.6.3: Jodi Johnson (right), Environmental Officer for the Department of Environment and Coastal Resources
with Ryan Sim (left), University of Waterloo Canada, using High Resolution Coastal Profile Surveying with an RTK
GPS.
Vertical measurements were adjusted according to the height of the receiver relative to the ground. The
water’s edge was fixed to a datum point of 0 for the field measurements, but later adjusted according to
tide charts. Generally, satellite connections were very good, receiving up to 10 satellites, resulting in submetre
accuracy. The mean vertical accuracy for all points was approximately 0.015 to 0.3 m while the
horizontal accuracy had a mean average of 0.015 to 0.2 m accuracy. Each transect point measurement was
averaged over 30 readings taken at 1 second intervals. At each point, the nature of the ground cover (e.g.
sand, vegetation, concrete) was logged to aid in the post-processing analysis. Ground control points (GCP)
were taken to anchor the GPS positions to locations that are identifiable from aerial photographs to
improve horizontal accuracy. These were taken where suitable landmarks existed at each transect location
and throughout the island. GCP points were measured over 60 readings at 1 second intervals.
Following the field collection, all of the GPS points were downloaded on to a Windows PC, and converted
into several GIS formats. Most notably, the GPS points were converted into ESRI Shapefile format to be
used with ESRI ArcGIS suite. Aerial Imagery was obtained from Google Earth, and was geo‐referenced using
the GCPs collected. The data was then inspected for errors and incorporated with other GIS data collected
while in the field. Absolute mean sea level was determined by comparing the first GPS point (water’s edge)
to tide tables to determine the high tide mark. Three dimensional topographic models of each of the study
sites were then produced from a raster topographic surface using the GPS elevation points as base height
information. A Triangular Irregular Network (TIN) model was created to represent the beach profiles in
three dimensions. Contour lines were delineated from both the TIN and raster topographic surface model.
For the purpose of this study, contour lines were represented for every metre of elevation change above
sea level. Using the topographic elevation data, flood lines were delineated in one metre intervals. In an
effort to share the data with a wider audience, all GIS data will be compatible with several software
applications, including Google Earth.
The high resolution imagery provided by this technique is essential to assess the vulnerability of
infrastructure and settlements to future SLR in the Turks and Caicos Islands. The imagery also has the ability
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