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Total electron content observations by dense regional and worldwide international networks of GNSS
(2018-06-01)
Tsugawa, Takuya
;
Nishioka, Michi
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Ishii, Mamoru
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Hozumi, Kornyanat
;
Saito, Susumu
Two-dimensional ionospheric total electron content (TEC) maps have been derived from ground-based Global Navigation Satellite System (GNSS) receiver networks and applied to studies of various ionospheric disturbances since the mid-1990s. For the purpose of monitoring and researching ionospheric conditions and ionospheric space weather phenomena, we have developed TEC maps of areas over Japan using the dense GNSS network, GNSS Earth Observation NETwork (GEONET), which consists of about 1300 stations and is operated by the Geospatial Information Authority of Japan (GSI). Currently, we are providing high-resolution, two-dimensional maps of absolute TEC, detrended TEC, rate of TEC change index (ROTI), and loss-of-lock on GPS signal over Japan on a real-time basis. Such high-resolution TEC maps using dense GNSS receiver networks are one of the most effective ways to observe, on a scale of several 100 km to 1000 km, ionospheric variations caused by traveling ionospheric disturbances and/or equatorial plasma bubbles, which can degrade single-frequency and differential GNSS positioning/navigation. We have collected all the available GNSS receiver data in the world to expand the TEC observation area. Currently, however, dense GNSS receiver networks are available in only limited areas, such as Japan, North America, and Europe. To expand the two-dimensional TEC observation with high resolution, we have conducted the Dense Regional and Worldwide International GNSS TEC observation (DRAWING-TEC) project, which is engaged in three activities: (1) standardizing GNSS-TEC data, (2) developing a new high-resolution TEC mapping technique, and (3) sharing the standardized TEC data or the information of GNSS receiver network. We have developed a new standardized TEC format, GNSS-TEC EXchange (GTEX), which is included in the Formatted Tables of ITU-R SG 3 Data-banks related to Recommendation ITU-R P.311. Sharing the GTEX TEC data would be easier than sharing the GPS/GNSS data among those in the international ionospheric researcher community. The DRAWING-TEC project would promote studies of medium-scale ionospheric variations and their effect on GNSS.
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A new expression for computing topside scale height for satellite-based communications
(2017-10-19)
Jamjareegulgarn, Punyawi
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Supnithi, Pornchai
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Hozumi, Kornyanat
;
Tsugawa, Takuya
It is well-known that the NeQuick 2 model provides analytical expressions showing a relationship between topside and bottomside ionospheres. Its bottomside thickness parameter (B2bot) is a key parameter for studying topside electron density profile (EDP) and topside parameters, and its topside scale height (Hsc) is also used to identify the topside electron density profile. The B2bot computed using ionogram-derived ionospheric parameters can be used to calculate the Hsc. Unfortunately, the Hsc computed by the original B2bot expression (Hsc old) are significantly higher than the scale heights obtained from digisondes (Hm) and the diurnal variations of the Hsc old are quite different from those of the Hm. Hence, a new expression of B2bot for computing the Hsc is suggested in this work relying on the available expressions of the NeQuick 2 model. Our results show that (1) the Hsc computed by the new expression of B2bot (Hsc new) are comparable to the Hm and the diurnal variations in Hsc new are the same trends as those in Hm; (2) all of the scale heights show diurnal variations with higher values during daytime than during nighttime and the secondary peaks can be found different local times relying on the locations; and (3) the peaks of scale height cause higher absolute differences between Hsc new and Hm (D SH).
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A correction factor of bottomside thickness parameter for computing TEC in global navigation satellite systems
(2017-10-19)
Jamjareegulgarn, Punyawi
;
Supnithi, Pornchai
;
Hozumi, Kornyanat
;
Tsugawa, Takuya
This paper proposes two new equations for computing the bottomside thickness parameter of the NeQuick 2 model with a correction factor (B2bot Pro2) and the simulated TEC values (TEC Pro). The main contributions of this work are twofold, i.e., 1) the proposed B2bot Pro2 equation can be used to compute the bottomside thickness whose trends and values are close to ones of the observed B0 (B0 obs) obtains from DPS-4 (Digisonde) and 2) the computed B2bot Pro2 are used to compute the TEC values without additional TEC observation by any devices and TEC computation. In this case, it is useful for some locations where there exist only ground-based ionosonde without TEC observation or TEC measurement doesn't work in some situations. The results show that the B2bot Pro2 have the same trends as the B0 obs. They are closer to the B0 obs, except at 13LT in June solstice and September equinox. The averages of absolute differences between B2bot Pro2 and B0 obs (avAD Pro2) are generally lower than about 8 km. They show that the B2bot Pro2 are close to the B0 obs with the improved percentages of higher than 80%. The TEC computed using the B2bot Pro2 equation (TEC Pro) in the nighttime are generally close to the observed TEC (TEC obs) compared with those in the daytime.
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Estimation of the single GPS-receiver bias using the gradient descent algorithm
(2016-09-06)
Chiablaem, Athiwat
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Supnithi, Pornchai
;
Klinngam, Somjai
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Panachart, Chaiwat
;
Saekow, Apithep
The ionospheric Total Electron Content (TEC) can be obtained from processing measurements of the dual-frequency Global Positioning System (GPS) receiver. The main sources of errors in the TEC calculation are satellite and receiver biases. In this paper, we apply the gradient descent algorithm on the receiver bias estimation. The TEC is derived from measurements at 12 dual-frequency GPS stations in Thailand. The criterion of receiver bias estimation is based on the minimum sum of the vertical TEC (VTEC) standard deviation method. The results show that the maximum receiver bias value is approximately 3.69 ns at UDON station, while the minimum value is -5.91 ns at SRTN station. The accuracy of the receiver biases from this algorithm is compared with the reference method. The maximum percentage deviation is about 7.5% at SRTN station. The percentage deviation of the minimum sum of the VTEC between the reference method and the proposed method from all stations are less than 0.05%. Thus, the proposed algorithm is a viable option to estimate the receiver bias.

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