Keyhole Imagery Coverage Spatial and Temporal analysis

Applications of remote sensing imagery at national or regional scales require complete area coverage by satellite images. The frequently utilized ETM, SPOT, and other imagery feature regular revisit periods, ensuring a relatively uniform spatial distribution of image coverage. However, Keyhole satellites were film-return satellites, and their lifetimes were short, ranging from several to dozens of days. Additionally, the ground resolution of different types of Keyhole imagery varies from sub-meter to tens of meters. Hence, the spatial coverage frequency and resolution of Keyhole satellites might exhibit notable spatial variability, potentially affecting the selection and application of Keyhole imagery data at national or regional scales.The study focuses on satellite imagery data from the USGS for a research area in China. The original vector data of the satellite imagery has been processed as follows:The imagery was categorized into three types based on resolution: meter-level, five-meter-level, and ten-meter-level, according to the classification in "Declassified Intelligence Satellite Photographs" (https://doi.org/10.3133/fs20083054).A 10 km interval grid of points was generated for the China region, and coverage information for each resolution type was collected for each grid point.The coverage frequency for each resolution type at each grid point was calculated.The annual imagery coverage area and average coverage frequency between 1960 and 1985 were calculated.Python 2.7 combined with ArcGIS 10.2 was used for processing, and code was provided for each step.