Cost-effective dual-frequency GNSS receivers: quality assessment for geophysical applications

Cost-effective multi-frequency GNSS receivers harbour opportunities for geoscientific displacement-monitoring applications, such as economically deploying large networks of accurate GNSS stations. We use the tinyBlack data logger, developed to facilitate such applications, to test the performance of such receivers. We first compare different receivers, independently of any built-in antenna quality, in a zero-baseline test. Two cost-efficient dual-frequency receivers (u-blox F9P and Swift Navigation Piksi Multi) and a tri-frequency Septentrio receiver (AsteRx-m3), housed in tinyBlacks, together with a stand-alone reference geodetic receiver (Septentrio PolaRx5), are simultaneously connected to a geodetic choke-ring antenna using a splitter. We analyse observation quality, including availability, multipath linear combinations, and signal-to-noise ratios. We process observations in a precise point positioning (PPP) scheme, with both daily-coordinate and kinematic solutions, and assess solutions and residuals. Results show the cost-efficient receivers are most affected by multipath effects and produce greater residuals and less accurate vertical coordinates, differing by more than 1 mm on average from the reference and higher-end receivers. A step-displacement test then evaluates the ability of the Piksi receiver to recover a repeated 5-cm displacement in two-hour cycles, in separate north-south and vertical subtests, using a geodetic rover antenna. We perform PPP processing without ambiguity resolution and compute the displacement in each cycle as the difference of average coordinates. Results show that the receiver can recover the average amplitude of repeated 5-cm displacements with sub-cm accuracy, also in the vertical direction, although the spread of individual recovered displacements and individual coordinates is greater than in the horizontal test.