Analysis of on-line PPP service (GDGPS - APPS) for Dual-frequency Receivers: a study involving data from RBMC stations

Abstract

The PPP (Precise Point Positioning) is a positioning method by GNSS (Global Navigation Satellite System) that has gained great popularity, due to on-line services for processing, most of them available for free. The PPP requires GNSS data from a unique receiver and the use of precise ephemeris and corrections. One of these freely available on-line PPP processing services is the APPS (Automatic Precise Positioning Service), a post-processed mode from NASA, and derivated from GDGPS (Global Differential GPS), which is a real-time GPS monitoring system with more than 100 globally distributed stations. This paper is focused on the evaluation of the APPS processing service to GPS data corresponding to a period of 30 days from the Brazilian stations POAL and IMPZ, respectively located in the South and North of Brazil, which belong to the official network of SIRGAS reference system. Each daily file contains 24 hours of observations with collection rate of 15 seconds, and it was processed time tracking of 2, 4, 6 and 24 hours. The daily coordinates of these stations, estimated by the PPP, have been updated to the SIRGAS2000 reference’s epoch (2000,4), and compared with the official station coordinates. The discrepancies to a time tracking of 24 hours showed root mean square error less than 2 cm, both in planimetry and altimetry, which attests the potential use of PPP/APPS in high-accuracy applications, as geodynamic studies. It also shows an improve of accuracy of few millimeters when the time tracking increases to four hours, and minor or statically similar error variances when the time was six hours.

Key words: GPS, GDGPS, Precise Point Positioning, APPS.