Synchronisation and Signal Delay Calibration in Passive Satellite Tracking
Abstract
Digital television signals received from a geostationary satellite can be used as signals of opportunity to calculate and predict the satellite orbit. This is an inexpensive and practical way to evaluate satellite collision risks, a key aspect of space surveillance and space safety. The technique is based on measuring the Time Difference of Arrival (TDoA) between pairs of tracking stations located across the satellite footprint, using a high-gain parabolic antenna and a signal digitiser. To calculate the TDoA accurately, the stations must timestamp the measurements according to a common time reference, which is achieved by using a GNSS receiver. Since the GNSS equipment setup can be different at each station (e.g., different cable lengths), it is necessary to calibrate the total GNSS chain delay and compensate for it. Also, the signal from the geostationary satellite itself undergoes a time delay as it travels across the tracking station hardware, which should also be accounted for. This paper describes GMV's Focusear passive tracking system, with an emphasis on signal delay calibration aspects.