Analysis and Prospect of the U.S. Army’s Decrypted Keyhole Satellite Program

The U.S. military launched the "Keyhole Satellite Project" (KeyHole) in the 1950s and recorded the surface and military conditions around the world. This batch of data was officially declassified in the 1990s and used for research on global changes and other fields. Keyhole satellite imagery, a remote sensing data set with earlier shooting time and high image quality, is exciting for researchers. However, compared with the extensive research and application of modern commercial satellites such as Landsat, Keyhole's related research is far from deep enough in modern science such as remote sensing or history. Starting from the dual perspectives of remote sensing and history, this article systematically sorts out the keyhole satellite program of the US military, expounds the background of its interpretation, analyzes its data characteristics, and introduces its decryption and downloading process. Then, taking the Shanghai area in 1965 as an example, the processing and image classification methods of historical images were discussed. This study will further enrich the research content of aerial images in the historical period, and provide a solid historical basis and data basis for the development of research in the pre-remote sensing era, especially the pre-Landsat period, and the research of forming a longer time series with Landsat and other data.