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    Statistical analysis of high frequency radio parameters on St. Patrick's day in Thailand
    (2017-10-19)
    Thammavongsy, Phimmasone
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    Supnithi, Pornchai
    ;
    Klinngam, Somjai
    ;
    Phakphisut, Watid
    ;
    Hozumi, Kornyanat
    The ionospheric irregularities on St. Patrick's day (17 March 2015) at Chiang Mai and Chumphon stations are affected by the strongest of the 24th solar storm cycle. The ionogram data in this research is obtained from the frequency modulated/carrier waves (FM/CW) ionosonde at Chiang Mai station and near the magnetic equator, namely, Chumphon station. The parameters in this research include the critical frequency of F2 layer, the virtual height of F layer, and the maximum height of F2 layer. Overall, we found that the ionosphere layer at Chiang Mai and Chumphon stations are disturbed by the geomagnetic storm. The result indicate that the radio frequency transmission is affected by geomagnetic storm at both stations and the observation differ from the median value is specified in part of the percentage of coefficient deviation.
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    Estimation of the single GPS-receiver bias using the gradient descent algorithm
    (2016-09-06)
    Chiablaem, Athiwat
    ;
    Supnithi, Pornchai
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    Klinngam, Somjai
    ;
    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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    The occurrence of equatorial spread-F at conjugate stations in Southeast Asia
    (2015-04-15)
    Klinngam, Somjai
    ;
    Supnithi, Pornchai
    ;
    Rungraengwajiake, Sarawoot
    ;
    Tsugawa, Takuya
    ;
    Ishii, Mamoru
    In this study, the probability of equatorial spread-F (ESF) occurrence at the conjugate stations in Southeast Asia: Chiangmai station (CMU), Thailand, and Kototabang station (KTB), Indonesia, and near the magnetic equator, Chumphon station (CPN), Thailand, is presented. We analyze the ionogram data recorded by the Frequency Modulated Continuous Wave (FM/CW) ionosondes for the periods of minimum solar activity from September 2008 to April 2009 and in the equinoctial months (March and April) from 2006 to 2013. The spread-F signatures are manually categorized into three types: the frequency spread-F (FSF), the range spread-F (RSF) and the mixed spread-F (MSF) and the monthly average percentage of the occurrence of each ESF type is presented. The results show that the percentage of RSF occurrence at CPN, which is located around the magnetic equator, is higher than at other stations and the RSF mostly occurs during the equinoctial months. On the other hand, the FSF occurrence at CMU and KTB, that are located in the northern and southern hemispheres, respectively, are higher than at CPN. The RSF occurrence typically has the peaks before midnight, while the maximum occurrence rate of FSF is after midnight. Furthermore, the RSF onsets normally precede the FSF onsets by about 1-2 h. As the solar activity levels go up, the percentages of RSF occurrence increase, but the percentages of FSF tends to decrease. In addition, we compare the statistics of observed RSF occurrence with the prediction of the IRI-2012 model. The results show that the IRI model overestimates the observed RSF occurrence at all stations during most of the solar activity levels and seasons, except in June 2008 (21:00-03:00 LT), March 2011 (23:30-01:00 LT) and March 2013 (01:00-02:30 LT) when the IRI model underestimates our observations. However, the IRI model gives closer probability of RSF occurrence to our observed values at CPN, especially in equinoctial months and during the periods of medium solar activity. This work is important for an improvement of the IRI model in the prediction of the spread F occurrence probability in the low-latitude region.
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    The statistics of equatorial spread-F at the conjugate stations in Southeast Asia
    (2014-01-01)
    Klinngam, Somjai
    ;
    Supnithi, Pornchai
    ;
    Manositthichai, Narongsak
    ;
    Sepsirisuk, Kasemsuk
    ;
    Tsugawa, Takuya
    Ionospheric disturbance is a major impediment to current communication systems with the signals propagating through the ionosphere. A signature of such disturbance when appearing in an ionogram, resulting from the ionosonde observation system, is known as spread-F. The spread-F statistics is therefore crucial to the design and operation of communication system. In this work, we analyze the equatorial spread-F (ESF) statistics at the conjugate stations: Chiangmai, Chumphon and Kototabang during the period of minimum solar activity from September 2008 to April 2009. The statistics of range type spread-F (RSF) occurrence after the local sunset are shown in terms of the monthly average percentage since it is related to the Equatorial Plasma Bubble (ESP). We found that the RSF occurrence is higher at Chumphon station, which is near the magnetic equator, than at Kototabang and Chiangmai stations. The maximum level occurs during March 2009 at Chumphon station and the higher rate mostly during the equinoctial months. In addition, we compare the observed RSF occurrence probability at Chumphon station with the IRI-2012 model prediction. The comparison results show that the IRI model overestimates our results in all seasons, most evidently in December Solstice, except the estimation in June solstice during 21:00-03:30 LT when IRI model underestimates the statistics of RSF occurrence. Nevertheless, the IRI model gives closer probability values in March equinox during 20:00-22:00 LT than other seasons. © 2014 IEEE.