Characterizing the Performance of a Low-Cost Dual Frequency GNSS Receiver: Enabling Distributed Arrays of Small Instruments (DASI) and Citizen Science Observations

Abstract:

A new low-cost dual frequency GNSS receiver is tested for its capability of observing Total Electron Content (TEC). The US $220 dollar SparkFun GPS-RTK2 board, featuring the ublox ZED-F9P GNSS chip, was used to calculate the Total Electron Content above Northern Michigan in the Summer of 2020. Using multiple programs, a user can obtain the dual frequency pseudo range and carrier phase measurements needed to calculate TEC. However, the process is not automatic, but I have developed a TEC calculator to simplify the process. The receiver outputs the GNSS data in Ublox’s proprietary raw (.ubx) format. The ubx files are converted to Rinex observation and navigation files by the use of an open sourced GNSS program package know as RTKLIB. From there, TEC can be derived by RINEX files. In which, the program calculates pseudo range-based STEC, phased-based STEC, phase-leveled STEC, and Vertical TEC. The program can also create a TEC vs Time plot. The TEC calculator algorithm was verified by comparing with a similar GPS GOPI-TEC program developed by Dr. Gopi Seemala. The GNSS receiver may also be connected to a Raspberry Pi processor to record GNSS data continuously. A script allows the Pi to log and record TEC automatically. Because of the high costs of professional grade dual frequency GNSS receivers, those who can afford to record and calculate TEC data is limited. A lower cost receiver enables citizen scientists to make TEC. However, a potential limiting factor is the accuracy of the TEC results from the low-cost receiver. To determine the quality of the low-cost receiver TEC, we compared the results with TEC calculated from a nearby LEICA GRX1200+GNSS receiver using a LEIAT504 antenna from the National Geodetic Survey’s CORS station MIGD located in the same city as the low-cost receiver.