I. I. Efishov

Use of GLONASS for studying the ionosphere

Results of using the Russian Global Navigation Satellite System (GLONASS) to measure absolute values of the ionosphere’s total electron content (TEC) are presented. Specific features of configurations and differences in parameters of GLONASS and GPS are given, and their impact on TEC evaluation is analyzed. The statistical analysis is also carried out for comparing the TEC measurement data obtained from the GPS and GLONASS observations; a high correlation between measurements of both systems is shown. Investigations have revealed that the use of both systems allows of extending the possibilities of their employment for studying the ionosphere’s structure and dynamics. To restore the diurnal behavior of TEC of the ionosphere above the observation station, the phase measurements are proposed to be taken as input data. Their advantage over the group measurements is not only their high accuracy but the fact that they are less subject to the multipath effect. The technique for processing the phase observations implemented for GLONASS is an essential part of the system for monitoring of the ionosphere over the European part of p]Russia, which is under development at the West Department of Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation.

Monitoring of phase fluctuations of GPS signals in polar ionosphere

Dual frequency measurements of differential carrier phase of GPS L1 (fl=1.6 GHz) and L2(f2=1.2 GHz) signals have been used to study the storm-time development of phase fluctuations in Antarctic region. We used GPS measurements of the International GPS service (IGS) network stations of MCM4 (78°S, ¿~80°), CASI 66°S, ¿~80°), MAWI 67°S, ¿~71°), DAVI (68°S, ¿~75°). The phase fluctuations are caused by the presence of irregularities of different are in high latitude ionosphere. The standard GPS measurement provided global network are sampled with 30 s. The interval enables to detect the ionosphere irregularities with scale more than tenth kilometers. For analysis of the data the temporal variations of differential carrier phase GPS signals along individual satellite passes was used. In this report we present an occurrence phase fluctuations with scale times¿30 min. which were caused by large-scale irregularities with the size more than 100 km. The slow fluctuations of differential carrier phase characterize the spatial and temporal variations of TEC along individual satellite passes. The strong TEC fluctuation as an enhancement of TEC relative phon was found out in polar stations. The enhancement of TEC was bigger than 2¿10 time relative background, while the TEC increase to 10¿15 TECU in interval about 5¿10 min. The duration of such structures was up 10¿20min. It was observed during storm as well as during modrate geomagnetic activity. We attributed the structures as occurrence of polar patches. The intensity of TEC fluctuations increased during geomagnetic activity. on the 4¿5 hour satellite passes 3¿6 numbers strong and some weak patches ordinary were detected. As the measure of patch activity we used the rate of TEC on 1 min interval (ROT).

Effects of the Solar Eclipse of March 20, 2015 on the Total Electron Content over Europe

The effect of the solar eclipse of March 20, 2015 on variations of the total electron content (TEC) in the ionosphere over Europe is analyzed based on GPS/GLONASS measurements at EUREF network stations. The specific feature of this eclipse is that it occurred under conditions of geomagnetic disturbance remaining after a strong geomagnetic storm on March 17, 2015. This made it more difficult to identify the effects of the solar eclipse. To detect these effects, diurnal TEC variations at individual stations were analyzed. The effect manifested itself as a TEC depression with the minimum close to the time of the maximum phase of the eclipse over the observation station. The effect was more pronounced in TEC variations along the individual passes of the satellites, appearing as a trough-like TEC depression. The diurnal variation of the TEC on the day of the eclipse was significantly different from the nearest control days, which made it difficult to determine the absolute magnitude of the eclipse effect. The space–time behavior of the TEC was represented in the form of TEC maps for the European region. For this purpose, concurrent GPS/GLONASS observations at more than 150 stations were used. A high space–time resolution of the maps made it possible to reveal the dynamics of TEC behavior over Europe during the event under consideration. The eclipse led to a clear change in the structure of the latitudinal and longitudinal TEC gradients. TEC maps generated with a 5-min resolution demonstrate the dynamics of the spatiotemporal behavior of the TEC during the eclipse.

Auroral Perturbations as an Indicator of Ionosphere Impact on Navigation Signals

A comparative analysis of total electron content (TEC) fluctuations and auroral activity, which characterizes the polar ionosphere during periods of substorm activity, is performed. The analysis is based on GPS/GLONASS observations at auroral and subauroral stations and data on auroral emissions obtained at the Yakutsk subauroral station and the Poker Flat (Alaska) auroral station. A detailed analysis is carried out for the storm on January 7, 2015. During this event, a sharp increase in the auroral activity and in TEC fluctuations from 09 to 13 UT was observed. A similarity of the dynamics of the auroral oval and the space–time distribution of TEC fluctuations associated with ionospheric irregularities in the oval is demonstrated. There is a close correlation between the positions of the auroral oval and the irregularity oval. The positions of the auroral oval, predicted by the NORUSKA Russian–Norwegian model, and of the TEC irregularity oval are compared. In general, the positions of the ovals are close to each other. The existing discrepancy may be due to the fact that the auroral oval is projected to an altitude of 110 km, whereas the irregularity oval, to an altitude of 450 km, and that the curvature of the magnetic force lines is not taken into account. The influence of auroral disturbances on navigational measurements manifests itself through the fact that, during disturbances, faults and failures in the operation of navigation equipment at auroral and subauroral stations increase.

Occurrence of TEC fluctuations and GPS positioning errors at different longitudes during auroral disturbances

In this work we analyzed the occurrence of the GPS TEC fluctuations associated with auroral disturbances during the storm on January 7, 2015. The impact of the disturbance on GPS precise positioning were considered. For this purpose, we used the observations of GPS stations located at the European, American and Asian sectors. The auroral activity was determined by data of the IMAGE magnetometers network. The rate of TEC (ROT) used as measure of the TEC fluctuation activity. The intensity fluctuations evaluated by index ROTI. The behavior of fluctuations on different longitudes is very similar. The comparison of substorm activity and the time evolution of the TEC fluctuations showed good consistency. The maximum intensity of TEC fluctuations was observed simultaneously (at the same UT time) over GPS stations which were located at different longitudes. In our work an impact of the geomagnetic disturbances on the Precise Point Positioning (PPP) errors was analyzed. The positioning errors were determined using the GIPSY-OASIS software (APS-NASA). The 3D position errors (P3D) reached the large values (more than 10 m) during storm, while they did not exceed 30 cm during quiet geomagnetic conditions. Our analysis showed the close relation between ROTI and the positioning errors. The positioning errors increased rapidly with increasing of ROTI.

Occurrence of GPS Phase Fluctuations in Northern and Southern Hemisphere

In paper presented analysis of storm-time occurrence of GPS phase fluctuations in high latitude ionosphere for the southern and northern hemisphere.

Occurrence of Phase Fluctuations of GPS Signals in the High Latitude Ionosphere During Geomagnetic Storms

Dual-frequency measurements of the differential carrier phase of GPS L1 (f1,= 1.575 GHz) and L2 (f2 = 1.228 GHz) signals have been used to study the development of phase fluctuations at high-latitude ionosphere during geomagnetic disturbances. The ionosphere irregularities are responsible for scintillations and phase fluctuations of GPS signals. Because of the depressive nature of the ionosphere the dual-frequency GPS phase measurements provide information about variations of the ionospheric total electron content (TEC). The paper analyses the occurrence of strong phase fluctuations of GPS observed at Antarctic stations. The fluctuations caused large scales ionospheric irregularities which were associated with occurrence of polar patches in TEC. The peculiarities of the latitude-longitudinal development of GPS signals phase fluctuations are described.