Influence of Precise Products on the Day-Boundary Discontinuities in GNSS Carrier Phase Time Transfer

Global navigation satellite system (GNSS) precise point positioning (PPP) has been widely used for high-precision time and frequency transfer. However, the day-boundary discontinuities at the boundary epochs of adjacent days or batches are the most significant obstacle preventing PPP from continuous time transfer. The day-boundary discontinuities in station estimates and time comparisons are mainly caused by the code-pseudorange noise during the analysis of observation data in daily batches, where the absolute clock offset is determined by the average code measurements. However, some discontinuities with amplitudes even more than 0.15 ns may still appear in station clock estimates and time comparisons, although several methods had been proposed to remove such discontinuities. The residual small amplitude of the day-boundary discontinuities in some PPP station clock estimates and time comparisons through new GNSSs like Galileo seems larger, especially using precise clock products with large discontinuities. To further understand the origin of the day-boundary discontinuities, the influence of GNSS precise products on the day-boundary discontinuities in PPP station clock estimates and time comparisons is investigated in this paper. Ten whole days of Multi-GNSS Experiment (MGEX) from modified Julian date (MJD) 59028 to 59037 are used as the observation data. For a comparative analysis, the station clock estimates are compared with global positioning system (GPS) and Galileo observations through PPP and network solutions, separately. The experimental results show that the daily discontinuities in current combined GPS final and rapid clock products are less than 0.1 ns, and their influence on the origin of day-boundary discontinuities in PPP station clock estimates and time comparison are statistically negligible. However, the daily discontinuities in individual Analysis Centers (ACs) GPS products are more extensive, and their influence on the origin of the day-boundary discontinuities in GPS PPP station clock estimates cannot be ignored. The day-boundary discontinuities demonstrate random walk noise characteristics and deteriorate the station clocks’ long-term frequency stability, especially at an average time of more than one day. Although Galileo clock daily discontinuities are different from those of GPS, their influence on the day-boundary discontinuities in station clock estimates is nearly similar to the GPS PPP. The influence of daily discontinuities of Galileo clocks on PPP time comparison is similar to GPS and is not particularly critical to time comparison. However, combined and weighted MGEX products should be developed or Galileo IPPP should be used for remote comparison of high-stability clocks.

Global distribution of persistence of total electron content anomaly

<p>Solar activities can disturb the ionosphere globally and induce ionospheric weather phenomena that transit rapidly through a large area. By contrast, sometimes the ionospheric plasma density can remain high or low over a certain location for a few days, which are difficult to be attributed to solar activities. This study shows the location preference of the positive and negative total electron content (TEC) anomalies persisting continuously longer than 24 hours (cross the two terminators) at middle and low latitudes (within ±60ºN geomagnetic latitudes). The TEC is obtained from the global ionospheric map (GIM) of the Center for Orbit Determination in Europe (CODE) (ftp://cddis.gsfc.nasa.gov/pub/gps/products/ionex) under the geomagnetic quiet condition of Kp ≤ 3o during the period of 2005–2018. There are a few (less than 4%) TEC anomalies that can persist over 24 hours. The persistence of the positive TEC anomaly along the ring of fire on the western edge of the Pacific Ocean. The high persistence of the TEC anomalies at midlatitudes suggests that thermospheric neutral wind contributes to the anomaly formation. The temporal and spatial anomalies of the ionospheric electric field, atmospheric electric field (flash), atmospheric gravity wave, and neutral wind over the ring of fire should be further examined for explaining whether the persistence of the TEC anomalies associates with lithospheric activities.</p>

Simple GPS Automatic Navigation Design

GPS vehicle navigation technology is the GPS technology emerges along with the rapid development of embedded technology, the auto industry, the market ofmore variety of products GPS navigation based on quality, technology gap, doesa variety of GPS products. This paper analyzes the development status ofdomestic and foreign vehicle navigation system at present, the GPS vehicle navigation system was discussed, to construct the hardware system based on embedded development board as the core, build of the vehicle navigation systembased on WinCE, using EVC and eSuperMap tool software, design of intelligent navigation system the electronic navigation maproute search.