Tale of Two RTNs: Rigorous Evaluation of Real-Time Network GNSS Observations

Abstract

Real-time networks (RTNs) have become popular for global navigation satellite system (GNSS) surveys because highly accurate positions can be derived in seconds to a few minutes compared with the many minutes and hours required with postprocessed static sessions. To evaluate the accuracy of these shorter-duration RTN GNSS observations and their potential for use as a source for establishing geodetic control, data collected from two National Geodetic Survey (NGS) surveys in South Carolina and Oregon were studied in detail. This article explores the horizontal and vertical accuracy of real-time observations as a function of observation duration, examines the influence of the inclusion of Globalnaya Navigazionnaya Sputnikovaya Sistema (GLONASS) observables, compares results from real-time kinematic (RTK) positioning using a single base station versus a network of base stations, and assesses the effect of baseline length on accuracy. Thirty-eight passive marks were repeatedly observed with GNSS using a RTN in the two study areas for a variety of different observation times, ranging from 5 s to 15 min. An optimal real-time observation duration was found in the range of 18 to 3 s. The real-time data acquired using a network of base stations tended to be more accurate and precise than single-base RTK data, especially vertically. Further, the addition of GLONASS observables helped obtain more fixed solutions at longer baseline lengths than solutions based solely on global positioning system (GPS) observables and showed a slight improvement in accuracy, particularly for stations with poorer satellite visibility.