a b s t r a c tWhen determining the absolute oblique total electron content (TEC) of the ionosphere using both GLON-ASS/GPS code and phase measurements, there occurs a systematic error associated with the differential code biases (DCBs). A 1-ns DCB leads to the $2.9 TECU error when determining L1-L2 dual-frequency oblique TEC. We have developed an algorithm for DCB estimation from the data of a single GPS/GLONASS station. Presented are the results of the algorithm operation compared with the oblique TEC correction by using CODE laboratory DCB data. Ó 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Global navigation satellite systems (GNSS) have enabled to study the ionosphere in different regions of the world [1]. One may say today that such studies have become global and have involved both more-or-less investigated mid-and equatorial latitudes and poorly investigated Arctic and Antarctic ones. The total electron content (TEC) of the Earth ionosphere can be determined from code and phase dual-frequency pseudorange measurements performed by receivers of GNSS signals. This technique is widely described in the literature [4].Phase measurements are weakly noised, but they are relative due to the ambiguity of the initial phase definition. Code measurements are absolute, however, they feature very high noise, up to hundred percent at low elevation angles. For this reason, to obtain the absolute TEC values, phase measurements are usually used, and the ambiguity is eliminated with code ones. Thus, there occurs a systematic error termed differential code biases (DCBs). DCBs depend on both satellite and receiver, and are related to that the signal transit times in radio frequency paths of the receiver and the satellite differ for the L1 and L2 ranges, and depend on the signal frequency. This error may significantly exceed the real TEC value and lead to obtaining unphysical negative TEC values [6].To determine the absolute TEC accounting for DCBs from the data of a single GPS/GLONASS station, we have developed the following algorithm:(1) To calculate the TEC from code I p and phase I u measurements.(2) To separate data sequences into continuous-time intervals.(3) To detect and eliminate the impact of outliers and signal tracking losses in the TEC data [2]. (4) To remove the ambiguity of phase measurements:where N is the number of measurements at a continuous interval. (5) To estimate DCBs by using a simple model of measurements.The model parameters are determined based on the minimization of the standard deviation between the experimental and model data (see below). (6) To correct TEC sequences obtained in item 4 by the DCB value.We use the following model of TEC measurements:where I V is the absolute vertical TEC value; D/ is the latitude difference between the ionospheric point coordinate / and that of the / 0 station; Dl is the longitude difference between the ionospheric point coordinate l and that of the l 0 st...

No abstract

Abstract. This study presents an analysis of the groundbased observations and model simulations of ionospheric electron density disturbances at three longitudinal sectors (eastern European, Siberian and American) during geomagnetic storms that occurred on 26-30 September 2011. We use the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) to reveal the main mechanisms influencing the storm-time behavior of the total electron content (TEC) and the ionospheric F2 peak critical frequency (foF2) during different phases of geomagnetic storms. During the storm's main phase the long-lasting positive disturbances in TEC and foF2 at sunlit mid-latitudes are mainly explained by the storm-time equatorward neutral wind. The effects of eastward electric field can only explain the positive ionospheric storm in the first few hours of the initial storm phase. During the main phase the ionosphere was more changeable than the plasmasphere. The positive disturbances in the electron content at the plasmaspheric heights (800-20 000 km) at high latitudes can appear simultaneously with the negative disturbances in TEC and foF2. The daytime positive disturbances in foF2 and TEC occurred at middle and low latitudes and at the Equator due to n(O) / n(N 2 ) enhancement during later stage of the main phase and during the recovery phase of the geomagnetic storm. The plasma tube diffusional depletion and negative disturbances in electron and neutral temperature were the main formation mechanisms of the simultaneous formation of the positive disturbances in foF2 and negative disturbances in TEC at low latitudes during the storm's recovery phase.

a b s t r a c tWhile estimating ionospheric total electron content (TEC) using both pseudorange and phase GPS/GLON-ASS data, there occurs a systematic error caused by the difference in processing times of L1 and L2 signals through radio frequency paths of satellites and receivers, known as differential code biases (DCBs). A 1-ns DCB causes an 2.9 TECU error in TEC estimation. Along with systematic DCB variations, seasonal variations, most likely related to variations in the receiver environment (temperature, humidity), also exist for some receivers and can reach in some cases up to 20 TECU. Ó 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Along with navigation and precise time applications, Global Navigation Satellite Systems (GNSS) are widely used nowadays to remotely sense the ionosphere in equatorial, mid-latitude and arctic regions [1]. Ionospheric TEC can be estimated using dual-frequency code and phase measurements of pseudo ranges between a satellite and a receiver [2]. While estimating absolute TEC using the code and phase measurements simultaneously, a satellite and receiver dependent systematic error occurs. This error is associated with the different, frequency dependent processing times of L1 and L2 signals in RF paths, both for satellites and receivers. Due to these biases (known as DCBs), TEC, in some cases, can obtain even non-physical negative values. For example, a 1-ns DCB causes an 2.9 TECU error (2.85 TECU for GPS and 2.92 TECU for GLONASS frequencies) in TEC estimation. Thus, one should take DCBs into account for precise absolute TEC estimations [4,5]. It is especially important for the analysis of long period TEC datasets obtained not only from GPS/GLONASS data but also from geostationary SBAS data [3]. Long period TEC datasets obtained from geostationary SBAS can have systematic change with time caused by DCB changing. This systematic change can be mistaken for ionospheric TEC changing. The complexity of evaluating DCB for geostationary SBAS data should be noted, since the elevation angle of geostationary satellites varies slightly and it is very difficult to separate the DCB from real TEC changes.In this work, for the first time, we analyze DCBs dynamics and errors in TEC estimations associated with satellites and receiver DCBs for 2000-2014. For such estimates, we used the CODE laboratory data (ftp://ftp.unibe.ch/aiub/CODE/) based on the measurements at the world wide IGS network (International GNSS Service) (http://igscb.jpl.nasa.gov/) of GPS/GLONASS receiving stations. All the results of DCB estimations shown below are presented in TEC units (1 TECU = 10 16 electrons/m 2 ). Fig. 1 shows an example of the dynamics (variability) of DCB dependent mean along all IGS station errors of TEC estimations for two satellites, GLONASS 04 and GPS PRN03. Note the systematic variability of the TEC estimation errors associated with DCBs, which is about 1 TECU/year for the GPS satellite and thr...