C42A-01 INVITED 10:20h
Photogrammetry for Glaciology
An "Introduction to Photogrammetry" is presented first and attention is called to some of the differences between satellite imagery and aerial photography. The application of some well-established aerial and terrestrial photogrammetry procedures, which have long been in general use for topographic mapping, to studies of glacier and ice sheet motion and extent is then discussed. Some examples of projects carried out by the first author are given: 1) surface motion studies from standard aerial mapping photography over relatively large areas (Byrd Glacier and one of the West Antarctic ice streams, Antarctica and Jakobshavn Glacier, Greenland), 2) studies of extent of relatively small pieces of ice from standard mapping photos (Mt. Kilimanjaro) and from unconventional, small-format photography (Deception Island, Antarctica) and 3) the application of terrestrial photogrammetry in the monitoring of the extent of Qori Kalis, the largest outlet glacier of the Quelccaya Icecap in the Peruvian Andes, over a period of more than 40 years. The results of the latter document accelerating rates of retreat of the terminus and loss of ice area and volume from 1963 to 2001. Retreat of the front was 42 times as fast between 2000 and 2001 as between 1963 and 1978. Since 2001, however, the retreat appears to have stopped, at least temporarily, as it did between 1991 and 1993. A proglacial lake formed sometime between 1983 and 1991 and presently covers about 31 ha.
C42A-02 INVITED 10:35h
Changing Vegetation and Fluvial Morphology in Northern Alaska Detected Using Aerial Photographs
Evidence from arctic Alaska suggests that the terrestrial landscape is changing in response to documented warming. Between 1946 and 1951, several thousand low-altitude panchromatic oblique aerial photographs were taken as part of geologic reconaissance and exploration of Alaska's Arctic Slope and Brooks Range. For this study, 202 of the old photographs were re-photographed. Comparison of the old and new photographs revealed an increase in shrub cover in the last half-century. The changes were observed over a 220,000 km^2 tract of arctic tundra, and it is likely that they are more widespread. A quantitative method for comparing the photographs yielded an increase in alder shrub cover from 14 to 20%, with similar increases observed for willow and birch shrubs. This shrub expansion was observed in many landscape positions, including hill slopes, river terraces, and also river floodplains, where the increase in vegetation has resulted in narrower, more stable floodplains. Changes were also observed at treeline. The pervasiveness of the change documented in the photographs can only be explained by a perturbation operating on a similarly large scale. In the absence of large-scale disturbances like fire, the increase in shrubs documented here is thought to be a product of elevated temperatures and other changes in climate favorable to shrub growth. Special attention will be given to the methods used to compare the old and new photographs.
C42A-03 INVITED 10:50h
POST-LITTLE-ICE-AGE LANDSCAPE AND GLACIER CHANGE IN GLACIER BAY NATIONAL PARK: DOCUMENTING MORE THAN A CENTURY OF VARIABILITY WITH REPEAT PHOTOGRAPHY
Historical photographs, many dating from the late-19th century are being used to document landscape and glacier change in the Glacier Bay area. More than 350 pre-1980 photographs that show the Glacier Bay landscape and glacier termini positions have been acquired by the authors. Beginning in 2003, approximately 150 of the sites from which historical photographs had been made were revisited. At each site, elevation and latitude and longitude were recorded using WAAS-enabled GPS. Compass bearings to photographic targets were also determined. Finally, using the historical photographs as a composition guide, new photographs were exposed using digital imaging and film cameras. In the laboratory, 21st century images and photographs were compared with corresponding historical photographs to determine, and to better understand rates, timing, and mechanics of Glacier Bay landscape evolution, as well as to clarify the response of specific glaciers to changing climate and environment. The comparisons clearly document rapid vegetative succession throughout the bay; continued retreat of larger glaciers in the East Arm of the bay; a complex pattern of readvance and retreat of the larger glaciers in the West Arm of the bay, coupled with short-term fluctuations of its smaller glaciers; transitions from tidewater termini to stagnant, debris-covered termini; fiord sedimentation and erosion; development of outwash and talus features; and many other dramatic changes. As might be expected, 100-year-plus photo comparisons show significant changes throughout the Glacier Bay landscape, especially at the southern ends of East and West Arms. Surprisingly, recent changes, occurring since the late-1970s were equally dramatic, especially documenting the rapid thinning and retreat of glaciers in upper Muir Inlet.
C42A-04 11:05h
Applications of modern digital terrestrial photogrammetry to problems in glaciology.
Recent developments in digital photogrammetry allow reliable, accurate, stereometric models of detailed objects such as glaciers to be constructed at reduced cost and effort in comparison to conventional film-based aerial or terrestrial photogrammetric methods. These developments include: 1) Correction of lens distortion by digital remapping of images; 2) Digital measurement of image space coordinate measurements; 3) Ease with which multiple stereomodels may be combined, permitting redundancy and strong parallax. These improvements make stereophotogrammetry a practical and cost effective alternative to other mapping procedures (e.g. optical survey, laser profiling) for small- to medium-scale glaciology projects. The relative strengths of digital terrestrial photogrammetry are compared to traditional film-based photogrammetric procedures as well as to other ground-based and airborne survey methods and satellite imagery, and several examples of terrestrial photogrammetric applications to glaciers are presented, including topographic profiling, velocity determination, and structural mapping.
C42A-05 11:20h
Snow and Glacier Monitoring Using Oblique Terrestrial Photography
This paper presents the use of photography for monitoring snow change at daily to weekly resolution in several sites of the European Alps. A novel technique for georeferencing oblique photography is presented. This procedure allows a relatively precise geolocation of pixels in a single photography with the aid of a DEM. Further radiometric and topographic corrections and image processing allow the estimation of surface albedo and the recognition of snow patterns and textures. Examples of successful applications are presented, such as for the validation of snow ablation and accumulation models, snow drift and energy balance. The dedicated software, which has been made open source and freely available will presented and explained.
C42A-06 11:35h
Uses of Several Photographic Methods to Detect Changes of Glaciers in Arctic Alaska
We have employed several photographic methods to detect changes on glaciers in Arctic Alaska. On Okpilak and McCall Glaciers in the eastern Brooks Range, we have re-occupied photo-locations from 1906 and 1958 respectively. These photos unambiguously document that a large loss of ice mass has been on-going here over the past 100 years. The Okpilak Glacier photos also unambiguously reveal that retreat from the most recently exposed moraines did not begin until near the turn of the century, supporting lichenometric evidence that the change in weather patterns that marked the end of the Little Ice Age here occurred sometime around 1890. A time-series of photos from this photo-site since 1906 reveals the influence of glacier geometry on volume loss rates. Comparing these photos with modern survey data has also allowed us to better quantify the ice loss observed. On McCall Glacier, we have employed time-lapse photography in several ways. By installing a camera on a ridge high above the glacier, we can watch the snow-line move up-glacier in summer. By placing a camera in the accumulation area in front of a large ruler, we can record the rate of snow accumulation throughout the year. By placing a camera in front of our weather stations located on the glacier surface, we can both improve our interpretations of the weather data as well as help troubleshoot the causes for equipment malfunctions. Because shading plays such an important role in patterns of surface mass balance in these steep mountain valleys, we have used both optical and infrared time-series of photos to document both shading and the resulting impact on surface temperature within the valley. We are also using these time-series to help validate models of surface energy balance that incorporate shading.
C42A-07 11:50h
Using Digital Imagery from a Small Unmanned Aerial Vehicle (UAV) to Estimate Arctic Melt Pond Coverage on Sea Ice
Photo mapping of melt pond coverage on sea ice was undertaken in the Arctic during the summer of 2004 using an Aerosonde. Aerosondes are small, long endurance UAV designed to undertake a wide range of operations in a highly flexible and inexpensive mode. The Aerosonde conducts a defined mission in a completely autonomous mode. All flights are under the command of a ground controller who can change missions and respond to air traffic control requests, etc. An NSF-funded effort (Office of Polar Programs' Long Term Observations [LTO]) is now underway to deploy Aerosondes for routine mapping and atmospheric sounding missions in the Arctic. Aerosondes were deployed at Barrow, AK, during June, 2004 as part of the LTO effort. During this deployment, several flights were dedicated to examining the fractional coverage of melt ponds over sea ice in the Beaufort and Chukchi Seas, as part of a study funded by NASA. Melt ponds have been identified as a key feature in determining the amount of solar insulation absorbed by sea ice, and hence is a primary controller of the melt rate of the ice through the summer. Sea ice models have, to date, crudely parameterized ponds, due in part to a lack of large-scale observations of their temporal and spatial evolution. The NASA-funded study uses observations from the EOS sensor MODIS to estimate pond fraction over a large portion of the Beaufort and Chukchi, by examining several spectral (visible and near-infrared) MODIS bands and deducing melt pond coverage from the known spectral properties of ponds. The Aerosonde flights dedicated to the melt pond study were necessary to test the validity of the pond coverage estimated using the MODIS data. A downward-looking Olympus C-3030 digital camera was mounted within the Aerosonde to photograph the sea ice. The digital photos are analyzed to classify each photo according to the percentage cover of melt ponds, unponded ice, and open water. These estimates are compared to the values retrieved using MODIS for the same area of coverage. To enhance these comparisons, missions were flown with 10 km x 10 km grid patterns, with overlapping (along-track and cross-track) digital photos, which allow for comparison with 400 MODIS pixels (500 m resolution). Additional missions were designed to examine the evolution of pond coverage over sea ice off the coast of Point Barrow, Alaska. The sea ice in this area of interest was fast ice (i.e. not drifting ice) and served as an area where melt ponds can be observed during formation and their evolution through the summer. The Aerosonde team flew several flights paralleling Point Barrow and overlapping in a pattern that provided contiguous digital camera images of the fast ice from shore to a few km off the coast. These flights were repeated several times during June, providing imagery that will assist investigators in determining how pond fraction changes over this period. The technique and results of pond coverage estimation from airborne digital photography will be presented, as will comparisons to estimates retrieved using MODIS.
C42A-08 12:05h
Study of Ice Sheet Basal Processes With Visible Light Images Acquired from a Borehole Probe
We have developed and deployed the JPL Ice Borehole Camera system into boreholes in two sites in Antarctica (and are deploying it in a third at the time of this meeting), and we have analyzed the image data to improve our understanding of processes at the bed of ice streams and the at basal surface of ice shelves. Though quite simple, the image data sets permitted interpretation of basal freeze-on associated with "binge and purge" processes of the Kamb Ice Stream as well as ice accretion processes, marine ice character and the marine ice-meteoric ice interface of the Amery Ice Shelf. In many ways the hot-water drilled hole is an excellent photographic environment for study of ice sheet phenomena; we are now examining means of augmenting simple digital imagery with additional optical, noninvasive interrogation strategies in order to obtain data on included particle properties, clathrate content, biological materials and phenomena, and on-going dynamic processes.