Estimation of GPS satellite antenna phase center offsets of the third frequency using raw observation model

Abstract

Satellite antenna phase center offsets (PCOs) is an important error source in global navigation satellite system (GNSS). With GNSS observations in a global network, the PCOs estimation strategy generally uses a dual-frequency (DF) ionospheric-free (IF) combination as the observation model. This model cannot derive the PCO values at each frequency, which results in the PCOs of the third frequency being unavailable for GPS satellites in the igs14.atx product. In this contribution, the PCOs estimation method of the third frequency based on uncombined (UC) precise orbit determination (POD) model is developed. The PCOs of the first- and second frequencies are fixed to the known values while PCOs of the third frequency are regarded as estimated parameters. This method is tested on the PCO estimation of GPS L5 frequency by using 110 ground stations throughout the entire year of 2018. The averaged standard deviations of L5 PCOs over one year are derived, with x-, y-, and z-offsets being 0.2, 0.2, and 1.6 cm, respectively. The corresponding difference values of the derived weighing averaged PCOs compared to the values of the igs14.atx product are 0.2, 0.1, and 9.9 cm. The POD experiment is processed to validate the derived PCOs of L5 over a period of 50 days. Results show that the accuracy of orbits, clocks and station positions is slightly improved after using estimated PCOs.