Optimization of the Correlation Range Receiver Parameters in SLR2000

Virtually all Satellite Laser Ranging (SLR) stations produce a real-time display known as an Observed-Minus-Calculated (OMC) plot. In such a plot, illustrated in Figure 1, the horizontal axis displays the elapsed time during the track while the vertical axis displays the measured ranges to the target plus any false alarms as points on the plot. The vertical axis is dynamically centered on the predicted round trip time to the target while the vertical width of the display corresponds to the range gate width, τg, which is chosen to reflect the a priori uncertainty in the range to the target. If we could predict the satellite orbits perfectly, the signal data would appear on our OMC plot as a narrow horizontal band in the center of a very narrow range gate. The width of the band, δ, would represent the overall timing precision of our instrument (including target effects) which, for modern SLR systems would have a total width between 3σ points on the order of 0.5 nsec or less for geodetic satellites. In reality, there is always a range bias (which moves the data vertically within that gate) and a time bias which, when multiplied by the range acceleration, introduces a slope σ in the OMC data display.