Accuracy of velocities from repeated GPS measurements

V Akarsu,E Arslan,D U Sanli

doi:10.5194/nhess-15-875-2015

Abstract

Abstract. Today repeated GPS measurements are still in use, because we cannot always employ GPS permanent stations due to a variety of limitations. One area of study that uses velocities/deformation rates from repeated GPS measurements is the monitoring of crustal motion. This paper discusses the quality of the velocities derived using repeated GPS measurements for the aim of monitoring crustal motion. From a global network of International GNSS Service (IGS) stations, we processed GPS measurements repeated monthly and annually spanning nearly 15 years and estimated GPS velocities for GPS baseline components latitude, longitude and ellipsoidal height. We used web-based GIPSY for the processing. Assuming true deformation rates can only be determined from the solutions of 24 h observation sessions, we evaluated the accuracy of the deformation rates from 8 and 12 h sessions. We used statistical hypothesis testing to assess the velocities derived from short observation sessions. In addition, as an alternative control method we checked the accuracy of GPS solutions from short observation sessions against those of 24 h sessions referring to statistical criteria that measure the accuracy of regression models. Results indicate that the velocities of the vertical component are completely affected when repeated GPS measurements are used. The results also reveal that only about 30% of the 8 h solutions and about 40% of 12 h solutions for the horizontal coordinates are acceptable for velocity estimation. The situation is much worse for the vertical component in which none of the solutions from campaign measurements are acceptable for obtaining reliable deformation rates.

Highlights

Today GPS is widely used to monitor crustal motion
Static GPS measurements have been the tradition for resolving large crustal motion
Repeated static GPS measurements, which were the desired methods in crustal motion monitoring starting from the end of 1980s, are still in use due especially to financial limitations and various other constraints

Summary

Introduction

Today GPS is widely used to monitor crustal motion. Methods of continuous GPS have been well established for this purpose (Mao et al, 1999; Williams et al, 2004; AmiriSimkooei et al, 2007) and are routinely used for monitoring tectonic motion. Researchers are studying real-time continuous GPS and high-rate GPS from the frequencies of 1 to 50 Hz GPS for the same purpose (Genrich and Bock, 2006; Blewitt et al, 2006, 2009; Larson, 2009; Avallone et al, 2011; Crowell et al, 2012). Researchers have studied the effect of observing session duration, baseline length and the network of reference stations on the accuracy of the static GPS (Eckl et al, 2001; Soler et al, 2006; Sanli and Engin, 2009; Firuzabadì and King, 2012). Repeated static GPS measurements ( known as GPS campaigns or episodic GPS), which were the desired methods in crustal motion monitoring starting from the end of 1980s, are still in use due especially to financial limitations and various other constraints. Based on various statistical methods, conclusions were drawn on the quality of the velocities derived from campaign measurements which are still in use today for monitoring crustal deformation

Analysis of GPS data

Evaluation procedure

Results and discussion

Conclusions