Implementation of quasi-real-time estimation of BDS clock

To obtain high reliability and accuracy of the zenith tropospheric delay more quickly, this study describes a parameter estimation method that uses an epoch-differenced and undifferenced function model to estimate the clock of the BeiDou navigation satellite system (BDS)/global positioning system (GPS) satellites using a quasi-real-time process. Forty-five MGEX tracking stations distributed globally were selected for study. The initial orbit information of the clock estimation used the ultra-rapid orbit products released by the German Research Center for Geosciences and post-products as reference values. The experimental results showed that the accuracy of the GPS satellite clock was better than 0.06 ns. The precision of clock for three kinds of BDS satellites was between 0.04 and 0.08 ns, slightly worse than the GPS. The estimated BDS clock appears to meet the demands for computing the quasi-real-time zenith tropospheric delay.