Tracking Glacial Activity in Norway with Photogrammetry Software
BAE Systems GXP
San Diego, Calif.
Based on historical tidal records, global sea levels have risen by approximately 0.17 meters since 1900, and recent predictions estimate that this trend will continue. Excluding thermal expansion, it is believed that 20 to 30 percent of this increase was caused by the melting of small glaciers, such as those in Svalbard, Norway, an area expected to make a disproportionate contribution to future sea-level rise because of its sensitivity to climate change.
In 2003, a group of researchers, led by a team of scientists from Swansea University, U.K. launched a field study named the Sea Level Rise from ICE in Svalbard (SLICES) project, designed to measure and calculate past and future sea-level rise among the archipelago called Svalbard. The purpose of the study was to gather historic topographic data sets for comparison with current records of the same area.
Because of logistical difficulties and a lack of knowledge pertaining to how the world's glaciers are changing, measuring and forecasting global sea-level rise is no small task — and there are few long-term mass balance studies for historical comparison.
However, while it is impossible to pinpoint exact timetables, advanced tools for collecting and analyzing information give researchers renewed optimism to expect more precise results than ever before.
|Figure 1 Perspective view (looking northeast) of a glacier in Svalbard, Norway called Slakbreen. The image, from 2003, shows a shaded-relief, LIDAR DEM interpolated to 2 meter overlaid with a change map relative to a 1961 DEM. The figure was created in QT Modeler from Applied Imagery.|
|Figure 2 Another LIDAR DEM of Slakbreen Glacier, illustrating the decrease in elevation over the 42-year period. Note that red areas show decrease of over 100 meters.|
|Figure 3 Vertical aerial photograph of Slakbreen in 1990. Photo is subset of aerial photograph S90 1987, © Norwegian Polar Institute|
The SLICES team, led by Professor Tavi Murray from the School of the Environment and Society, Swansea University, includes a host of prestigious co-investigators and partners such as the Universities of Bristol and Newcastle upon Tyne, the Norwegian Polar Institute, British Antarctic Survey, NASA, University of Silesia, and the Russian Academy of Sciences.
Between 2003 and 2005, the team collected accurate GPS control data, aerial photography, LIDAR, and optical data of nine benchmark glaciers around the Svalbard archipelago. Statistics from other expeditions, collected during the same timeframe, were also available.
The primary goal was to measure volume changes of the benchmark Svalbard glaciers, using LIDAR and photogrammetrically derived digital elevation models (DEMs), to provide a strong baseline for continued monitoring in the area. The findings were applied to the entire archipelago with a regional mass balance model, which was used to derive 20th and 21st century contributions to global sea-level rise in Svalbard.
There were four main objectives:
- Address the baseline length limitation of LIDAR collection — the decay in the accuracy of post-processed data caused by the distance between the aircraft and the nearest GPS reference station — and overcome the logistical limitations of working in remote areas.
- Derive estimates of historical mass balance for the 20th century for a representative sample of Svalbard glaciers.
- Scale the results to arrive at an estimate of sea-level rise contribution for the archipelago.
- Forecast sea-level rise contributions for the 21st century under different climatic scenarios.
The glaciers around Svalbard could make the largest contribution to sea-level rise of any arctic region outside of Greenland. According to Dr. Timothy James, scientist at Swansea University, “Ice masses around the world are changing rapidly. The Glaciology Group within the School of the Environment and Society at Swansea is using advanced digital terrain modeling techniques with SOCET SET as our key photogrammetric data capture package to improve the quantification and our understanding of these changes.”
For the SLICES project, there were many large images that had been captured at 1:50,000 scale and scanned at a high resolution to maximize DEM resolution. SOCET SET's flexibility with large images, input file formats and ASCII files was a major advantage. SOCET SET's Automatic Terrain Extraction (ATE) and Interactive Terrain Editing (ITE) modules offer a combination of automated and manual tools for building terrain and surface models, and work equally well with new and century-old data.
Stereo matching on surfaces such as glaciers with repeating patterns and a lack of texture is notoriously difficult. Through the use of back-matching algorithms in ATE, the scientists have been able to eliminate many of the blunders that are normally associated with stereo matching on such surfaces, and thus obtain a better automated DEM with far less manual correction required.
Figure 4 Graph shows centerline profiles of Slakbreen for each of the four years for which topographic data are available. Data for 1961, 1977, and 1990 were all derived from aerial photographs using photogrammetry, and 2003 data is from a LIDAR DEM. These results showing rapid decay are typical in the west of Svalbard.
Occasionally, in extremely steep areas, or areas where fresh snow cover makes stereo matching difficult, the team implements a hybrid approach, which involves measuring DEM points or breaklines manually in ITE, then using these as seed points in ATE. If stereo matching is unreliable, for example in areas of fresh snow with little texture, it is preferable to have a hole in the data, as opposed to blunders. A TIN (Triangulated Irregular Network) DEM, produced in ATE with back-matching, yields much better results; it will identify such points as blunders and discard them.
Results from study of the Slakbreen glacier (The Slak Glacier) are illustrated in Figures 1–4. Figures 1 and 2 show 2003 shaded-relief LIDAR DEMs. The image of Slakbreen is overlaid with a color-coded illustration that depicts elevation change of the glacier surface since 1961 which was calculated using the 1961 DEM generated photogrammetrically in SOCET SET. The scale shows surface lowering of over 100 meters. Since 1961, the snout (front or terminus) of Slakbreen has retreated 1.4 km, with a significant portion of the melt occurring in the past 10 years.
|Figure 5 2005 photo of Midre Lovénbreen in northwest Svalbard.|
|Figure 6 2005 shaded-relief LIDAR DEM of Midre Lovénbreen in perspective view shaded by elevation.|
|Figure 7 1990 aerial photo of Midre Lovénbreen with GPS checkpoints overlaid. Photo is subset of aerial photograph S90 6526, © Norwegian Polar Institute.|
|Figure 8 Calving (fracturing) front of Monacobreen in northwest Svalbard (in 2004) with zodiac for scale (small inflatable boat for short trips).|
Evidence suggests that this is characteristic at least on the west side of the Svalbard archipelago. Mass balance measurements of selected benchmark glaciers in Svalbard were made using contemporary and historical aerial photographs controlled using contemporary LIDAR DEMs. This approach provides both well distributed and long-term mass balance measurements.
Figures 5-7 show the Midre Lovénbreen glacier in photos, in LIDAR and with GPS checkpoints overlaid. The glacier, like Slakbreen, has experienced significant melting over the last 40 years. Between 1961 and 2005, the ave-rage rate of melt was found to be about 0.47 meters vertically per year, with more melt occurring in recent years.
Climate change is a cause for concern to the scientific community and the general public. Small glaciers like those in Svalbard represent only four percent of the world's total land ice, but account for an estimated 20 to 30 percent of 20th century sea-level rise — and the melt has increased substantially since 1988. This work is extremely important for improving predictions of sea-level rise due to the density of population along the world's coastlines. To appreciate the scale of these glaciers, note Figure 8 and cover of this magazine.
Looking ahead, the Swansea Glaciology Group is turning their attention to Greenland, an area that has been identified as crucial for predicting future sea-level rise. Their new project, Greenland Ice Margin Prediction, Stability and Evolution (GLIMPSE) aims to examine the Greenland ice sheet through collaborative research using fieldwork, remote sensing, and modeling studies. To help make this project possible, GLIMPSE will provide an exciting opportunity for private sector organizations to become involved in groundbreaking Greenland research. For details on these and other projects underway within the Swansea Glaciology Group, please visit: geography.swan.ac.uk/glaciology/
Note LIDAR data courtesy of the Natural Environment Research Council Airborne
Remote Survey Facility in the U.K.
Aerial photographs were provided by the Norwegian Polar Institute. The SLICES project would like to thank BAE Systems for their support with SOCET SET (www.baesystems.com/gxp) and Applied Imagery (www.appliedimagery.com) for providing their Quick Terrain Modeler software.