A novel in-flight geometric calibration method for mapping cameras with composite-frame

The new aerial mapping cameras usually have a large-format frame to satisfy the dual demand of a wide field-ofview (FOV) and high resolution. One of the main techniques is to utilize a composite-frame composed of integrated multiple arrays. However, in-flight geometric calibration (IGC) is still a challenge for ensuring the metric accuracy of composite-frame cameras. In this paper, we propose a new method for IGC of a novel compositeframe mapping camera, and verify its accuracy and applicability. The method mainly consists of geometric test field design and crossing route self-calibrating bundle adjustment with additional parameters. It can overcome the strong correlation of the solved parameters, which occurs among the additional parameters, the internal orientation, the external orientation element, and other unknowns. This method can also avoid the problems of aggravated computation results or non-convergence. Using a 1200 m x 1200 m test field on a flat terrain, we tested the method on the composite-frame mapping camera DMZ II in 2021. The results demonstrate that the method fulfills the calibration requirements of the composite-frame camera, and can overcome the negative effects of flat terrain conditions. The calibration accuracy reaches the level of 0.1 pixel, corresponding to the geometric error of less than 1 um, and the parameters can effectively describe the distortion distribution of the composite-frame. It was successfully applied to practical aerial photogrammetry engineering in Jiayuguan area in 2022. In addition, the algorithm for generating distortion free images after calibration has been updated, using indirect correction combined with free network adjustment to suppress the random error caused by various factors over long periods of time, in order to improve the quality and robustness of computational imaging. The method offers a reliable and efficient way for IGC of large-format aerial cameras with composite frames, greatly reducing the requirements for ground calibration fields, while also providing valuable references for other aerial and space mapping cameras that adopt integrated arrays imaging mechanism.