Accuracy improvement of zenith tropospheric delay estimation based on GPS precise point positioning algorithm

In the precise point positioning (PPP), some impossible accurately simulated systematic errors still remained in the GPS observations and will inevitably degrade the precision of zenith tropospheric delay (ZTD) estimation. The stochastic models used in the GPS PPP mode are compared. In this paper, the research results show that the precision of PPP-derived ZTD can be obviously improved through selecting a suitable stochastic model for GPS measurements. Low-elevation observations can cover more troposphere information that can improve the estimation of ZTD. A new stochastic model based on satellite low elevation cosine square is presented. The results show that the stochastic model using satellite elevation-based cosine square function is better than previous stochastic models.