Abstract
A newly available portable unit with GNSS raw data recording capability is assessed to determine static and kinematic position accuracy in various environments. This unit is the GPSMap 66, introduced by Garmin in early September. It is all-weather and robust for field use, and comes with a helix antenna. The high sensitivity chipset is capable of acquiring and tracking signals in highly attenuated environments. It can track single frequency GPS, GPS + GLONASS or GPS + Galileo and record code, Doppler and carrier phase data every second in the RINEX format. The evaluation presented herein focusses on GPS and Galileo. Static and kinematic test results obtained under a wide range of realistic field conditions are reported. Differential GNSS methods and Precise Point Positioning (PPP) are used to assess absolute position accuracy in ITRF coordinates, which is sufficiently close to the GPS and Galileo reference frame for the current purpose. Under low multipath conditions, measurements are found to be sufficiently accurate to provide single epoch, bias free position accuracy of a few metres. Accuracy is a function of signal attenuation and multipath conditions. The use of an external geodetic antenna significantly reduces measurement noise and multipath in high multipath environments. Carrier phase measurements, available more or less continuously under open sky conditions, significantly improve performance in differential mode. Accuracy in vehicular mode using code and carrier phase differential RTK solution is at the level of a few to several dm. Tests were conducted in parallel with a Huawei P10 Android 8.0 smartphone. The code measurement noise of this unit was found to be significantly higher than that of the GPSMap 66, a major reason being its lower performance PIFA antenna; carrier phase was only available for short time intervals, significantly degrading differential position accuracy performance.
Highlights
Android smartphones that can record raw GNSS pseudorange measurements have been available since late 2016 and initial results have shown promising potential for positioning (e.g., [1,2])
The results demonstrate the capability of the GPSMap 66 for Precise Point Positioning (PPP) applications at the 1 m RMS or better level under low ionospheric conditions
The realistic static and kinematic tests conducted in this study with the robust hand held GNSS
Summary
Android smartphones that can record raw GNSS pseudorange (and most recently carrier phase) measurements have been available since late 2016 and initial results have shown promising potential for positioning (e.g., [1,2]). The data can be processed in real-time or post-mission In the latter case, online precise point positioning (PPP) services are available to process data collected in static or kinematic mode. Online precise point positioning (PPP) services are available to process data collected in static or kinematic mode Open source software such as RTKLib (rtklib.org) is available for single point and differential processing. Low cost portable and wearable units with high sensitivity GNSS chips, similar to those available in smartphones, have been available for years for a variety of applications.
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