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

Lately, multi-frequency GNSS signal availability have become more commonplace, while dual-frequency receiving capability, previously restricted to expensive geodetic-grade instruments, appeared in cost-efficient and low-cost receivers. Therefore, large networks of GNSS stations with high positioning accuracy can now be deployed at limited cost, benefitting a variety of geoscience applications.

To take advantage of the developments in dual-frequency capabilites, GFZ and spin-off company maRam developed the tinyBlack GNSS receiver. The tinyBlack is compact, robust, versatile and low-power. It is equipped with one of various GNSS receiver boards and can be integrated with additional sensors. It provides a flexible, economical solution for geoscientific monitoring stations for, e.g., tectonic, volcanic and earth engineering monitoring. We evaluate the geodetic performance of different dual-frequency receiver boards in the tinyBlack.

We conduct a zero-baseline test, comparing three different receiver boards (Septentrio AsteRx-m3, Ublox  and SwiftNav Piksi) in a tinyBlack receiver and a separate, reference receiver (Septentrio PolaRx5). All boards have at least dual-frequency (L1/L2, E1/E5b) support and were simultaneously connected to a static geodetic choke-ring antenna. We first check data quality with GNut/Anubis, including observation availability, multipath linear combination, and signal-to-noise ratio. We then analyse PPP solutions with GFZ-provided precise orbits and satellite clock offsets, computing both daily and sub-daily kinematic coordinates. We compare observation residuals, coordinate estimates, and troposphere estimates. We find that the Ublox and Piksi receivers struggle more with multipath effects than the geodetic-grade receivers, despite using the same antenna in a good test location with a clear view of the sky. We also find that the Piksi has fewer observations, including a hard-coded low-elevation-angle cutoff. Probably as a consequence, it also the highest signal-to-noise ratio and lower residuals than the Piksi. PPP daily coordinate performance is vertically worse than, and horizontally comparable horizontally with, the cost-efficient receivers. Sub-daily coordinate performance is worst with the Piksi.

We also conduct a test step-wise moving antenna test to evaluate the capability of the Piksi receiver specifically to recover known displacement. We move the antenna by 5 cm every hour, alternatively forwards and backwards in a repeated 2-hour cycle, both horizontally (north-south) and vertically in separate tests. We compute kinematic PPP solutions with GFZ-provided precise orbits and clock offsets. We find that the average amplitude of the step can be recovered successfully and that both the standard deviation of the amplitudes and the scatter of coordinates at each point in the cycle is greater for the vertical component.

We finally perform data quality controls and show network-solution estimated coordinates of four GNSS stations in a field installations. The stations are co-located with seismometers installed in Italy as part of the DETECT (DEnse mulTi-paramEtriC observations and 4D high resoluTion imaging) project, which aims to acquire a dense multiparametric dataset imaging near-fault, active, slow tectonic deformation in a portion of the southern Apennines mountains with destructive historical seismicity.

In conclusion, we appreciate the developments spurred by the availability of dual-frequency signals and look forward to further field applications of dual-frequency receivers for geoscience research.