• Journal of Positioning, Navigation, and Timing
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• v.8 no.2
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• pp.69-77
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• 2019

This study introduces MATLAB Graphical User Interface (GUI)-based software to monitor ionospheric disturbances. This software detects ionospheric disturbances using Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS) measurements, and estimates a location of the disturbance source through the detected disturbance. In addition, this software includes a sky plot making function and frequency analysis function through wavelet transform. To evaluate the performance of the developed software, data of 2011 Tohoku earthquake in Japan were analyzed by using the software. The analysis results verified that the ionospheric disturbances were detected through GPS and GLONASS measurements, and the location of the disturbance source was estimated through the detected disturbance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.8
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• pp.549-557
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• 2019

In this paper, we focus on the real-time detection method of a seismic ionospheric disturbance using Global Navigation Satellite System (GNSS) signal. First, the monitor for the detection of the seismic ionospheric disturbance is studied based on the estimated ionospheric delay using the GNSS signals. And then, the threshold for the automatic detection is computed. Moreover, to discriminate the seismic ionospheric disturbance against the other ionospheric anomalies due to other error sources such as cycle slips, the signatures of the ionospheric perturbation caused by the seismic wave is investigated. Based on the observation, the detection strategy is proposed. Using GPS observations collected from the 47 permanent stations in South Korea and Japan, the proposed real-time detection method is evaluated.

• Publications of The Korean Astronomical Society
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• v.15 no.spc2
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• pp.1-13
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• 2000

Through the coupling between the near-earth space environment and the polar ionosphere via geomagnetic field lines, the variations occurred in the magnetosphere are transferred to the polar region. According to recent studies, however, the polar ionosphere reacts not only passively to such variations, but also plays active roles in modifying the near-earth space environment. So the study of the polar ionosphere in terms of geomagnetic disturbance becomes one of the major elements in space weather research. Although it is an indirect method, ground magnetic disturbance data can be used in estimating the ionospheric current distribution. By employing a realistic ionospheric conductivity model, it is further possible to obtain the distributions of electric potential, field-aligned current, Joule heating rate and energy injection rate associated with precipitating auroral particles and their energy spectra in a global scale with a high time resolution. Considering that the ground magnetic disturbances are recorded simultaneously over the entire polar region wherever magnetic station is located, we are able to separate temporal disturbances from spatial ones. On the other hand, satellite measurements are indispensible in the space weather research, since they provide us with in situ measurements. Unfortunately it is not easy to separate temporal variations from spatial ones specifically measured by a single satellite. To demonstrate the usefulness of ground magnetic disturbance data in space weather research, various ionospheric quantities are calculated through the KRM method, one of the magneto gram inversion methods. In particular, we attempt to show how these quantities depend on the ionospheric conductivity model employed.

• Korean Journal of Remote Sensing
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• v.34 no.6_4
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• pp.1531-1544
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• 2018

We detected the coseismic ionospheric disturbance generated by the earthquakes of magnitude 5.0 and greater in Korean Peninsula. We considered the seismic events such as Gyeongju earthquake in September 2016 with magnitude 5.8, the Pohang earthquake in November 2017 with magnitude 5.4, and the underground nuclear explosion from North Korea in September 2017 with magnitude 5.7. Although all GPS stations were not detected, the ionospheric disturbance induced by these earthquakes occurred approximately 10-30 minutes and 40-60 minutes after the events. We inferred that the time difference within each variation is due to the different focal depth and the geometry of epicenter, satellite, and GPS station. In the case of the Gyeongju earthquake, the earthquake had relatively deeper depth than the other earthquakes. However, the seismic magnitude was bigger and it occurred at nighttime when the ionospheric activity was stable. So we could observe such anomalous variations. It is considered that the ionospheric disturbance caused by the difference in velocity of the upward propagating waves generated by earthquake appears more than once. Our results indicate that the detection of ionospheric disturbances varies depending on the geometry of the GPS station, satellite, and epicenter or the detection method and that the apparent growth of amplitude in the time series varies depending on the focal depth or the site-satellite-epicenter geometry.

• Journal of Astronomy and Space Sciences
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• v.32 no.4
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• pp.297-304
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• 2015

In this study, we documented the midlatitude F2-layer response to five strong geomagnetic storms with minimum Dst < -150 nT that occurred in solar minimum years using hourly values of the F2-layer critical frequency (foF2) from four ionosondes located in different hemispheres. The results were very limited, but they illustrated some peculiarities in the behavior of the F2-layer storm. During equinox, the characteristic ionospheric disturbance patterns over the Japanese station Wakkanai in the Northern Hemisphere and the Australian station Mundaring in the Southern Hemisphere were consistent with the well-known scenario by $Pr{\ddot{o}}lss$ (1993); however, during a December solstice magnetic storm, both stations did not observe any noticeable positive ionospheric disturbances. Over the "near-pole" European ionosonde, clear positive ionospheric storms were not observed during the events, but the "far-from-pole" Southern Hemisphere station Port Stanley showed prominent enhancements in F2-layer peak electron density in all magnetic storms except one. No event produced noticeable nighttime enhancements in foF2 over all four ionosondes.

• Journal of Advanced Navigation Technology
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• v.22 no.2
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• pp.49-56
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• 2018

As the energy generated by earthquake, tsunami, etc. propagates through the air and disturbs the electron density in the ionosphere, the perturbation can be detected by analyzing the ionospheric delay in satellite signal. The electron density in the ionosphere is affected by various factors such as solar activity, latitude, season, and local time. To distinguish from the anomaly, therefore, it is required to inspect the normal trend of the ionosphere. Also, as the perturbation magnitude diminishes by distance it is necessary to develop an appropriate algorithm to detect long-distance disturbances. In this paper, normal condition ionosphere trend is analyzed via IONEX data. We selected monitoring value that has no tendency and developed an algorithm to effectively detect the long-distance ionospheric disturbances by using the lasting characteristics of the disturbances. In the end, we concluded the $2^{nd}$ derivative of ionospheric delay would be proper monitoring value, and the false alarm with the developed algorithm turned out to be 1.4e-6 level. It was applied to 2011 Tohoku earthquake case and the ionospheric disturbance was successfully detected.

• Bulletin of the Korean Space Science Society
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• 1995.10a
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• pp.18-18
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• 1995

No Abstract, See Full Text

• Journal of Positioning, Navigation, and Timing
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• v.11 no.3
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• pp.157-161
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• 2022

The Nuri rocket developed by South Korea was launched at approximately 07:00 UT on June 21, 2022. We use GPS observations obtained from the Korean GNSS network to analyze ionospheric total electron content (TEC) disturbances induced by the 2022 Nuri rocket launch. TEC disturbances are observed south over South Korea 4-5 min after the rocket launch. In addition, the maximum depletion in the vertical TEC shows approximately 8 TEC units (TECU). We also compute a horizontal velocity from initial ionospheric disturbances triggered by the 2022 Nuri rocket launch. Its velocity is about 1.4 km/s. It may be related to the rocket's flight trajectory at the observation time of the ionospheric TEC disturbance.

• Publications of The Korean Astronomical Society
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• v.15 no.spc2
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• pp.21-25
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• 2000

The ionosphere, the atmosphere of the earth ionized by solar radiations, has been strongly varied with solar activity. The ionosphere varies with the solar cycle, the seasons, the latitudes and during any given day. Radio wave propagation through or in the ionosphere is affected by ionospheric condition so that one needs to consider its effects on operating communication systems normally. For examples, sporadic E may form at any time. It occurs at altitudes between 90 to 140 km (in the E region), and may be spread over a large area or be confined to a small region. Sometimes the sporadic E layer works as a mirror so that the communication signal does not reach the receiver. And radiation from the Sun during large solar flares causes increased ionization in the D region which results in greater absorption of HF radio waves. This phenomenon is called short wave fade-outs. If the flare is large enough, the whole of the HF spectrum can be rendered unusable for a period of time. Due to events on the Sun, sometimes the Earth's magnetic field becomes disturbed. The geomagnetic field and the ionosphere are linked in complex ways and a disturbance in the geomagnetic field can often cause a disturbance in the F region of the ionosphere. An enhancement will not usually concern the HF communicator, but the depression may cause frequencies normally used for communication to be too high with the result that the wave penetrates the ionosphere. Ionospheric storms can occur throughout the solar cycle and are related to coronal mass ejections (CMEs) and coronal holes on the Sun. Except the above mentioned phenomena, there are a lot of things to affect the radio communication. Nowadays, radio technique for probing the terrestrial ionosphere has a tendency to use satellite system such as GPS. To get more accurate information about the variation of the ionospheric electron density, a TEC measurement system is necessary so RRL will operate the system in the near future.

• Ocean and Polar Research
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• v.26 no.3
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• pp.489-499
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• 2004

The climatological characteristics of the polar ionospheric currents obtained from the simultaneous observations of the ionospheric electric field and conductivity are examined. For this purpose, 43 and 109 days of measurements from the Chatanika and Sondrestrom incoherent scatter radars are utilized respectively. The ionospheric current density is compared with the corresponding ground magnetic disturbance. Several interesting characteristics about the polar ionosphere are apparent from this study: (1) The sun determines largely the conductance over the Sondrestrom radar, while the nighttime conductance distribution over the Chatanika radar is significantly affected by auroral precipitation. (2) The regions of the maximum N-S electric field over the Chatanika radar are located approximately at the dawn and dusk sectors, while they tend to shift towards dayside over the Sondrestrom radar. The N-S component over Son-drestrom is slightly stronger than Chatanika. However, the E-W component over Chatanika is negligible compared to that of Sondrestrom. (3) The E-W ionospheric current flows dominantly in the night hemisphere over Chatanika, while it flows in the sunlit hemisphere over Sondrestrom. The N-S current over Chatanika flows prominently in the dawn and dusk sectors, while a strong southward current flows in the prenoon sector over Sondrestrom. (4) The assumption of infinite sheet current approximation is far from realistic, underestimating the current density by a factor of 2 or more. It is particularly serious for the higher latitude region. (5) The correlation between ${\Delta}H\;and\;J_E$ is higher than the one between ${\Delta}D\;and\;J_N$, indicating that field-aligned current affects ${\Delta}D$significantly.