TOKYO -- Nippon Telegraph and Telephone has developed a computer algorithm for swift analysis of data from satellite images to spot changes to terrain over time with a resolution of 3 meters.
Comparisons now done by eye and requiring many hours of work can be completed in a flash using this program. Satellite images covering all of Japan's roughly 388,000 sq. km can be analyzed in less than 18 hours, while a person would need a year to check just 30,000 sq. km of terrain.
Final analysis and judgment calls still need to be done by people, but the Japanese company's algorithm can identify where geographical features have changed due to a natural disaster, buildings on formerly empty land or other alterations such as those resulting from illegal harvesting or dumping.
The program does not look at the actual satellite images transmitted from space, but rather the compressed data for those images. Terrain changes are detected by comparing the same location in past and present images and measuring the amount of data used to encode each pixel. When a building occupies what had been an empty lot, for example, the number of bits used for those pixels is much greater.
An NTT group company will use the algorithm in the spring to update its professional maps. It will evaluate the program's effectiveness and prepare a business offering terrain map analysis to other companies.