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In this study, the locations of 193 old aerial photographs of northern Alaskan landscapes were rephotographed and assessed for changes in vegetation. The original photographs were taken over northern Alaska between 1948 and 1951, and the new photographs were taken between 1999 and 2003. The region covered by the original and repeat photographs stretches from the southern extent of the Brooks Range in the south to the Coastal Plain in the north, and from the Chukchi Sea in the west to the Canning River in the east. Approximate coordinates are 68°N to 70°N and 145°E to 164°E.
The original photographs were taken by the U.S. military as part of geologic reconnaissance and exploration, and the method used to acquire them was to fly both sides of a river valley while photographing the river and the facing valley slopes. Of the several thousand original photographs, only a fraction were repeated for the purpose of assessing vegetation change. Repeat photographs were selected for geographic coverage and to produce the greatest likelihood of detecting vegetation change. The original and repeat photographs were then scanned and stored in TIFF format. Individual image file sizes range from 5 to 60 MB each, and the total file size for the data set is 11 GB. The photographs are distributed on a set of three DVDs.
The images should not be published without the consent of the investigators.
Sturm, M., and C. Racine. 2005. A Half-Century of change in arctic Alaskan shrubs: a photographic-based assessment. Boulder, CO: National Snow and Ice Data Center. DVD.
To broaden awareness of our services, NSIDC requests that you acknowledge the use of data sets distributed by NSIDC. Please refer to the citation below for the suggested form, or contact NSIDC User Services for further information. We also request that you send us one reprint of any publication that cites the use of data received from our Center. This helps us to determine the level of use of the data we distribute. Thank you.
| Category | Description |
|---|---|
| Data format | Digital photographic images are in TIFF format. Associated reference files are in Excel format. |
| Spatial coverage and resolution | Coverage includes Northern Alaska, particularly the North Slope and Brooks
Range. Southernmost latitude: 68° N Northernmost latitude: 70° N Easternmost longitude: 145° E Westernmost longitude: 165° E |
| Temporal coverage and resolution | Original photographs were taken between 1948 and 1951; repeat photographs were taken between 1999 and 2003. |
| File naming convention | Files are named according to the photograph location number (see the "concat" tab in the Excel file "GPS_photo_locations.xls"), and specified as "new" or "old." |
| File size | Total data set size is 11 GB. Individual image file sizes range from 5 to 60 MB each. |
| Parameter(s) | The parameter is vegetation cover. |
| Procedures for obtaining data | To request a copy of the DVDs, complete the Data Order Form. |
1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information
Matthew Sturm
USA-CRREL-Alaska
Ft. Wainwright, AK, USA
Charles Racine
Environmental Science Branch
US Army CRREL
Hanover, NH, USA
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org
This study was supported by "A Half-Century of Change in Arctic Alaskan Shrubs: A Photographic-Based Assessment." National Science Foundation award OPP-0119374.
Between 1948 and 1951, the U.S. military took several thousand black-and-white oblique aerial photographs of Alaska's North Slope as part of geologic reconnaissance and exploration. Their efforts focused on the major rivers of the North Slope and the Brooks Range. The photos were used to interpret the structural geology of the region and to locate oil-bearing rocks. The method used to acquire the original photographs was to fly both sides of a river valley while photographing the river and facing valley slopes. Some flight lines also included landscapes of open tundra. The photographs, all taken during the summer months, were acquired with such rapidity and regular frequency that the terrain coverage was continuous down most rivers.
Repeat photographs were taken between 1999 and 2003. Of the several thousand original photos, only a fraction were repeated for the purpose of assessing vegetation changes. Old photographs were chosen to be repeated based on their geographic distribution, the presence of shrubs in the photos, and for the greatest likelihood of detecting change. Because birch and willow have a similar brightness to tundra, the repeat photography focused primarily on darker, more distinct alder shrubs.
The camera used for the original photographs (an early Fairchild) was too cumbersome to use for the repeat photos, so the investigators used a medium format Mamiya RZ67 Pro II camera with Kodak Portra 400 ASA color film. F-stops varied to maintain shutter speeds of 1/250 and 1/400 seconds. The investigators considered using black-and-white film for the repeat photography, but chose to use color film because the photographs could be converted to black-and-white images and because people seeking to repeat the photographs in the future would likely prefer the additional information contained in the color images. The investigators also chose film over digital format because of its enhanced resolution and permanence as a method for storing data. The original and repeat photographs were scanned using a Nikon Super Coolscan 8000, and pairs of photographs were cropped to provide the best possible matches.
The scanned photographs are stored digitally as Tagged Image File Format (TIFF) files. Associated reference files are in Excel format.
The files are grouped into folders according to photograph number and location. Each folder contains both the original and repeat photographs. The Excel file "GPS_photo_locations.xls" contains photograph location numbers and coordinates for the repeated photographs. The file "map.JPG" shows the general locations of the photographs.
DVD 1 contains folders for photographs taken along the Colville River, Nanushuk River (S), Kurupa River, Chandler River, Anaktuvuk River (N), Anaktuvuk River (S), Nanushuk River (N), and Oolamnagavik River. This disk also contains the associated reference files "GPS_photo_locations.xls" and "map.JPG." The file "map.JPG" shows the general locations of the photographs.
The file "GPS_photo_locations.xls" contains five pages:DVD 2 contains folders for photographs taken at the following locations: Sag/Lupine confluence, Itigaknit, Sagwon, Ivishak River, Kokolik River, Atigun Gorge, Upper Colville River, Horseshoe/Castle, The Notch, Canning River, and Upper Nigu River.
DVD 3 contains folders for photographs taken along the Ayiyak River, Upper Killik River, Nimiuktuk River, and Kugururok River.
Within each folder, files are named by their photograph location numbers (see the "concat" tab in the Excel file "GPS_photo_locations.xls") plus a "new" or "old" designation. For example, "11-20old.tif" indicates an original photograph of the Nanushuk river basin, while "11-20new.tif" indicates a new photograph of the same location.
Total data set file size is 11 GB. Individual image file sizes range from 5 to 60 MB each.
The photographic study was conducted in northern Alaska, particularly the North Slope, and covers a region from the southern extent of the Brooks Range in the south to the Coastal Plain in the north, and from the Chukchi Sea in the west to the Canning River in the east. Locations include: Colville River, Colville River near Umiat, Upper Colville River, Nanushuk River, Kurupa River, Chandler River, Anaktuvuk River, Oolamnagavik River, Sag/Lupine confluence, Itigaknit, Ivishak River, Sagwon, Kokolik River, Atigun Gorge, Horseshoe/Castle, The Notch, Canning River, Upper Nigu River, Ayiyak River, Upper Killik River, Nimiuktuk River, and Kugururock River.
Southernmost Latitude: 68° N
Northernmost Latitude: 70° N
Westernmost Longitude: 164° E
Easternmost Longitude: 145° E
The original photographs were taken between 1948 and 1951; repeat photographs were taken between 1999 and 2003.
The parameter is vegetation cover.
These small photographs are for demonstration purposes only. Actual files are large, high-resolution TIFF images.
11-20old.jpg (Nanushuk river basin)
11-20new.jpg (Nanushuk river basin)
Producing a new photograph with the same perspective as an old photograph was very difficult. As the helicopter approached an old photograph location, the pilot counted down the distance to the GPS point. When the helicopter reached the point, the pilot slowed the aircraft, and the investigators took the photograph; however, sometimes the location entered into the helicopter GPS was not exactly the location from which the original photograph was taken, and it was often necessary to direct the pilot left, right, up, or down. Sometimes the helicopter needed to circle back and reattempt the photograph from a slightly different location.
Pairs of photographs were cropped to provide the best possible matches between old and new photographs.
To request a copy of the DVDs, complete the Data Order Form.
The camera used to take the original photographs was an early Fairchild camera that produced 18x9 in. negatives. The new photographs were taken with a medium format Mamiya RZ67 Pro II with Kodak Portra 400 ASA color film that produced 6x7 cm. negatives.
Although the photographs technically qualify as aerial photographs, they are in fact low-angle obliques. The repeat photographs were taken from a helicopter with the doors removed, using a resection technique to determine the locations from which the original photographs were taken. This process involved determining the angles separating known geographic features in the original photographs and using a three-arm protractor to infer the position of the camera on a map. After two summers' experience, the investigators found that they could determine camera locations with sufficient accuracy using terrain features from the photographs and a map, but without resection calculations. The investigators guessed the altitude of the original aircraft flights. During the summers of 1999-2003, the investigators entered the old camera locations into a helicopter GPS, reoccupied the positions, and rephotographed the landscapes from about the same perspective as the original photographs.
Old and new photographs were scanned using Nikon Super Coolscan 8000, and the images were saved in TIFF format.
The original photographs were taken from a fixed-wing aircraft by the U.S. military as part of explorationand geologic reconnaissance. The repeat photographs were taken from helicopter by M. Sturm and C. Racine.
Sturm, M., C. Racine, and K. Tape. 2001. Increasing shrub abundance in the Arctic. Nature 411: 546-547.
4 April 2005
26 May 2005
May 2005
http://nsidc.org/data/docs/arcss/arcss130/index.html
