Satellite Laser Ranging Track Separation and Automated Reduction

Tracks in range residual plots, made up of repeated successful detections of returning laser light pulses reflected from satellite targets, must be identified and separated from the surrounding noise before full-rate and normal point data files can be formed for submission to the ILRS. Post-processing can begin shortly after the observed satellite has passed over the station using the recorded raw epoch-ranges and the required time can be taken to ensure that all observations, including those with weaker or intermittent signals, sloping tracks and tracks obscured by high levels of background noise, are successfully reduced. As for efforts within the ILRS global network to automate aspects of SLR operations, if this post-processing task could be fully automated it could bring improved efficiency and consistency. This paper describes novel methods developed at the Space Geodesy Facility, Herstmonceux, UK to automatically extract SLR data from background noise. The SLR track is first flattened by applying corrections to the orbit prediction. Track selection is achieved by taking the interval to the Nth closest point as a measure of the surrounding density for every data point and then setting a relative track threshold. A new high resolution estimate of return rate is used to filter the track data. A new method for clipping returns from flat panel GNSS laser retro-reflector arrays at different elevations is described. The resulting normal points are tested against those produced manually at the SGF.