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This part deals with the surveying of the south-facing ice cliffs of the Northern Icefield. The instrument used was a Trimble 5600 scanning reflectorless total station. It operates by moving equal-interval, pre-determined angles of arc, (dependant upon scanning resolution), and obtaining X, Y and Z coordinates of each of the observed points. By observing sufficient points it is possible to produce a quasi-continous surface of the surveyed area.

Two sections were studied, a broad, near vertical area, which is detailed and discussed here, and a second, smaller area with some very different features, the details of which can be found here. Essentially the same approach was used for both sections. Time precluded high resolution surveys covering both areas, so broad, low resolution scans were initially obtained which were then followed my more detailed scans of significant features.

The first scan was designed to capture a major section of the ice cliff, (approximately 100 metres in length). To capture as much detail as possible within a reasonable time frame the cliff was scanned with a horizontal resolution of 2 metres and a vertical resolution of 1 metre. Due to intermittent cloud the scan was completed in two parts and successfully combined to produce a scan of 1362 points. The derived grid to produce the surface seen in Figure 1 was defined with a 0.5m interval in X and Y with an isotropic kriging interpolation. In addition, breaklines were surveyed to define the top and bottom edges of the cliff and were included in the interpolation algorithm.

Figure 1. A front-on view of the main scanned ice cliff

Figure 2 An oblique view of the main scanned ice cliff

As this is a digital elevation model it can be viewed in any number of ways. For example Figure 2 shows a simple change in viewing angle.

Additionally it can be viewed as a more traditional contour plot as seen in Figure 3.Any number of profiles can be extracted from the model. Figure 3 also displays the location of two profiles that are then shown as cross-sectional profiles in Figure 4. Using this technique profiles can be extracted from the same location but at different scan times, showing changes over time.

Figure 3 Contour plot of the main ice cliff showing location of two profiles

Figure 4 Two cross-sectional profiles across the main ice cliff

Within the larger cliff section a smaller area was chosen to represent and highlight the vertical features that appeared similar in form to rill-like erosional features that may be found, for example, in badlands. The chosen area is highlighted in Figure 5.

Figure 5 The main scanned ice cliff showing the area chosen to highlight specific features

Figure 6 Comparison of the vertical section between the original scan (left) and the more detailed scan (right)

The vertical section shown highlighted in Figure 5 was scanned in two sections. The upper section, (approximately two-thirds) was scanned at a horizontal resolution of 0.3 metres and a vertical resolution of 0.75 metres and the lower section was scanned at a horizontal resolution of 0.25 metres and a vertical resolution of 0.5 metres. As opposed to the first general scan, this scan attempted to capture the vertically-aligned ridges and gulleys and therefore the horizontal resoloution was less than the vertical resoloution. This resulted in a total of 2,184 data points which were then used to create a grid with a 0.1 metre interval in both X and Y. Figure 6 shows a visual comparison between the surfaces from the general scan (left) and the more detailed scan (right). As can be seen the the latter defines the detail much more clearly and can be used to investigate the behaviour of specific features.

To further show the versatility of the system, Figure 7 shows the result of 'draping' a photograph over the DEM. The view shown here is from directly above the ice cliff looking down vertically to the surface below, even though the photograph was actually taken from the surface looking up at the ice cliff. Initially the photograph needed to be georeferenced to the coordinate system used for the scans. This was carried out by obtaining coordinates, (using the total station), of points identifiable in the photograph as well as on the ice cliff. From this the orientation and scale of the photograph could be calculated and then registered on the elevation model. In addition, the model required rotating so that is was in the same plane as the photograph.

Figure 7 A constructed view looking over the edge of the ice cliff down to the surface of the crater