Modelling the acquisition times of CORONA satellite photographs: accuracy and application.

In contrast to modern satellite images, information regarding the time of acquisition of declassified CORONA satellites is not readily available and requires access to hard-copy frame ephemeris data held by the US National Archives and Records Administration (NARA). In this article, the accuracy of a method described previously (Fowler 2006) for estimating the acquisition times of CORONA photographs using freely available historical Two Line Element orbital ephemeris data together with a commercial off-the-shelf modelling package for satellite operations has been investigated. The Root Mean Square Error (RMSE) between the modelled and documented acquisition times for a sample of 21 frames acquired by four CORONA KH-4B missions was determined to be of the order of 20.3 s and indicates that the approach can be used to estimate the acquisition times of CORONA satellite photographs to a relatively high degree of accuracy. From this, the solar azimuth and elevation for particular locations covered by the photographs can be readily determined. An example of the application of the technique is given for the case of two CORONA photographs of the landscape around the Roman siege-works at the fortress at Masada, Israel, and where knowledge of the solar lighting conditions at the time of acquisition enables the appearance of the archaeological features in their landscape setting to be appreciated. Being quick and low cost, this modelling approach has a broader utility for studies where knowledge of the acquisition times of CORONA satellite photographs is required. [ABSTRACT FROM AUTHOR]