Radio Techniques for Probing the Terrestrial Ionosphere
Lin, M. Kamogawa, Y I.
Radio techniques for probing the terrestrial ionosphere
Lin, B. Huang, S.
Yu, and Y H. Yeh, Coseismic ionospheric disturbances triggered by the Chi-Chi earthquake, J. Lin, H. Chen, and M. Kamogawa, Ionospheric disturbances triggered by the 11 March M9. Maruyama, T. Tsugawa, H. Kato, A. Saito, Y. Otsuka, and M. Nishioka, Ionospheric multiple stratifications and irregularities induced by the off the Pacific coast of Tohoku Earthquake, Earth Planets Space, 63, this issue, —, Rolland, L.
Radio Techniques for Probing the Terrestrial Ionosphere
Kherani, N. Kobayashi, M. Mann, and H. Munekane, The resonant response of the ionosphere imaged after the off the Pacific coast of Tohoku Earthquake, Earth Planets Space, 63, this issue, —, Smith, A. Titheridge, J. Tsai, H. Liu, C. Lin, and C. Chen, Tracking the epicenter and the tsunami origin with GPS ionosphere observation, Earth Planets Space, 63, this issue, —, Download references. Correspondence to Jann-Yenq Liu. Reprints and Permissions. Search all SpringerOpen articles Search.
Letter Open Access Published: 27 September Seismo-traveling ionospheric disturbances of ionograms observed during the M w 9. Abstract In this paper, sequences of ionograms recorded by 4 ionosondes in Japan and 1 in Taiwan are employed to examine seismo traveling ionospheric disturbances STIDs triggered by the 11 March, , M 9. Full size image.
Observation and Results A magnitude M 9. Table 1.
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Locations, distances to the epicenter and traveling times of the ionosonde. Ionospheric disturbances can affect technologies in space and on Earth disrupting satellite and airline operations, communications networks, navigation systems. As the world becomes ever more dependent on these technologies, ionospheric disturbances as part of space weather pose an increasing risk to the economic vitality and national security.
Having the knowledge of ionospheric state in advance during space weather events is becoming more and more important.
Therefore, a team in Neustrelitz is working on monitoring, modelling and forecasting the ionosphere for many years. Example of monthly median absorption at 2. Each line represents the attenuations as in Figure 12 , averaging the values along a month only echoes from 95 to km are considered. The curves extend only from approx. Even after such a simple study it is possible to note that in all the months the maximum attenuation occurs at noon local time , mostly due to the D layer. The measurements carried out by the AIS ionosonde, like all measurements, are affected by errors that now will be evaluated.
There are two general types of causes for errors:. All errors are expressed in dB, which is the most suitable unit when dealing with gains or attenuations and so it is convenient also to express errors in the same unit. Given that dBs express ratios, it is possible to demonstrate that the error figures, known and expressed in dB, can be combined in the same way as if they were relative errors in linear units , for which the resulting error is given as a quadratic average.
In other words, to combine two errors, characterised by a standard deviation in dB equal to E dB 1 e E dB 2 , the resulting error can easily be calculated with:. The first type of error can be minimised by calculating averages a simple average of linear values. During calibration output fluctuations were observed see Figure 7 and it is possible to establish a standard deviation for this type of error of about 0.
Analysing the second type of errors is more difficult, because they can be included among the systematic errors. It is assumed that the measured system parameter values transmitted power, cable attenuation, etc. To increase the measurement reliability, the calibration and measurements are carried out in the most controlled and stable conditions possible, for example waiting for the thermal stabilisation of the equipment.
Analysing this type of error in more detail, three error categories can be defined:. The errors in category a are due to the accuracy of the laboratory instrumentation; this item of data is considered to be 0.
There are two different measurements: cable attenuations and transmitted power the Tx and Rx cables were established in a single measurement, connecting them in cascade , so the resulting error is given by 5 : 0. Category b includes measurements of attenuations due to cable-antenna mismatches. These mismatches cause a small attenuation of the energy flowing from the transmitter to the transmitting antenna, and from the receiving antenna to the receiver.
It is difficult to directly measure this mismatch because of the particular antenna configuration, so mismatch attenuation is determined by means of calculations based on the measurement of the reflected energy at the cable-antenna transition, measured at the other end of the cable. Ultimately the error is evaluated by suitable analysis of error propagation using the conversion formula. This analysis produced a very small value, about 0.
Type c errors are the most complicated to evaluate, since it is impossible a directly measure the antenna gain, so this has to be determined using computer simulations. Unfortunately there are many factors that cause antennas to deviate from a free space behaviour, the main ones being the characteristics of the terrain and the presence of obstacles. Some structures buildings, trees, other antennas, and the antenna masts used to hold them in position near antennas can alter their radiation pattern and simulating these effects is somewhat difficult. The behaviour of the terrain is easier to deal with, but it varies over time, mainly due to changes in humidity.
The assessment of antenna gain performed during the calibration procedure on the AIS ionosonde was carried out without taking into account nearby structures but only the ground properties. The results gave an estimation of the error in antenna gains the sum of the gains of the two antennas within 0. This type of error cannot be properly defined as systematic, because ground properties can vary within a few hours.
Even though the nearby structures were not taken into account, at least an approximate evaluation of their influence needed to be made, so the presence of an adjacent antenna positioned near the active one was assessed the second antenna is used in different times, so it is considered passive when AIS is active.
It is thought that the effect of the second antenna is probably the most significant one compared to the other structures, and it influences the overall gain by 2. Table 2 summarises all the figures mentioned in this section. Finally, it needs to be recalled that all systematic errors should only be considered for the absolute measurements, while for the relative measurements Equations 2 and 4 they cancel out and only the random receiver errors remain considered twice , plus those due to the terrain. So the residual error is:. These conclusions are interesting because they show that the main component of the absolute error is due to the imperfect characterisation of the antennas.