BY LAWTON TAM
JUNE 28, 2002
CORONA Satellite Photography: An Application
Corona is the name of a U.S. program which acquired reconnaissance photography from satellites between 1960 - 1972. In 1995, the photography was declassified and became available, "the result of their potential for a better understanding of environmental and climatic changes."
Corona photography has several unique advantages:
- global coverage is extended backwards by 12 years [coincidentally the first ERTS/Landsat was launched in 1972, the same year the Corona program ended],
- high resolution: 40 - 6 ft., depending on camera,
- stereo coverage with later cameras.
One example of the application of this photography is U.K. Imperial College's expedition to Bogda Shan in 2000. Bogda Shan is a mountain range in Xinjiang Province, China. It lies to the east of the city of Urumqi, between the city and the Turfan Depression. The area is remote and there is a lack of reliable map coverage.
"The main objectives of the expedition were to study the geological evolution of the Bogda Shan .... and its effect on geomorphology." The area has remarkable topographic contrast: some peaks in Bogda Shan are over 5,500 m while the adjacent Turfan Depression has the second lowest point on Earth at -154 m.
One task of the expedition was glacial mapping. GPS was used in the field for present conditions. Results were compared with 1990 Landsat data [reported resolution 28.5 m in multispectral and 15 m in panchromatic mode] and Corona photography taken in 1963 and 1970 [reported resolution < 3 m] to determine the extent of glacial retreat.
The process of geo-referencing data, critical for accurate mapping, was handicapped by a lack of topographic maps. Landsat imagery was the most accurately geo-referenced but had the lowest resolution. Therefore small changes were indiscernible. Corona photography is high resolution but registration to Landsat data could not be done to better than 120 m. Theoretically, if 1: 25,000 mapping is available, changes [over time] as determined by combining GPS coordinates with Corona data can be accurate to within 20 m [ sphere-of-error radius. ]
Attempts to produce DEMs from the stereoscopic Corona photography were reported to be unsuccessful at time of writing because of technical problems.
In spite of the shortcomings, "geo-rectified" Corona photography was also used as a base for geological work and for mountain navigation because of its high resolution.
The web site www.bogdashan.co.uk though partly completed at present, has more details.