Speaker
Description
Small objects in the Low Earth Orbit pose unique challenges for tracking, as they are too faint for producing the well-identifiable streaks in images acquired in sidereal tracking mode. The solution is to use the optical instrument in object tracking mode. A particular property of the LEO objects is their high speed, which demands small camera exposure times. Even so, the background stars will be depicted as large streaks, making the astrometric calibration difficult. An even greater challenge is the fact that modern CMOS astronomical cameras use the rolling shutter exposure, each image row being exposed at a different moment in time. This behaviour does not affect sequences acquired with large exposure times (tens of seconds), but becomes critical when the exposure time is comparable with the total frame sweep time. In our case, the sweep time was 250 ms, and the exposure time 200 ms, meaning that the rolling shutter induced motion will be highly visible. Our solution to this problem was to compute a star displacement speed vector, based on the orientation of the streaks in the image, and scale this vector with the time stamp difference relative to the middle image row. By compensating for this displacement, we were able to match the centres of the star streaks with catalog stars and perform astrometric calibration, leading eventually to successful reduction of the LEO sequence.