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Comparison between foF2 observations and IRI-2001 model predictions at Thailand equatorial latitude station
(2008-10-06)
Wichaipanich, N.
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Boonchuk, T.
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Leelaruji, N.
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Hemmakorn, N.
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Supnithi, P.
In this paper, the comparison between the F2-layer critical frequency (foF2) observations and international Reference Ionospheric (IRI) model predictions is presented. The data used for this study are obtained from bottomside ionogram recorded by the FM/CW ionosonde at Chumphon campus of King Mongkut's Institute of Technology Ladkrabang (latitude 10.72°N and longitude 99.37°E), Thailand, located near the magnetic equator. The measurement data coverage from January to December of a low solar activity year (2006) is analyzed based on the diurnal, seasonal variation and then compared with IRI-2001 model predictions. Generally, the foF2 obtained from the IRI (URSI and CCIR) model closely follows observed foF2 values. Comparing the results of URSI and CCIR options for foF2, we find that for low solar activity, both the URSI and CCIR options of the IRI model give foF2 values close to the ones measured at Chumphon, but the CCIR results produce smaller range of deviation than the URSI results. All comparative studies give feedback for new improvements of CCIR and URSI IRI models. ©2008 IEEE.
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Modeling and measurement of airplane flutter phenomena on TV broadcasting signal
(2008-06-01)
Wongkeeratikul, A.
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Supnithi, P.
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Noppanakeepong, S.
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Leelaruji, N.
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Hemmakorn, N.
This paper presents a novel approach to model TV signal due to airplane flutter phenomena. The three components of the modeling are based on 1) Bistatic radar cross sections (RCS) of an ellipsoid, 2) 3-dimensional geometry consideration technique to calculate the distance difference between direct and reflected waves due to airplane, and 3) Ray theory, based on physical and geometrical consideration. Unlike previous works, the model takes into account of realistic parameters such flying height, distance from the airport, flying angle, altitude, aircraft body type and others. The simulation results are then compared with measurement results at 60.75 MHz and 208.75 MHz. The results have shown good agreement between simulation and measurement patterns. © 2008 IEEE.
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Low latitude ionosphere-thermosphere dynamics studies with inosonde chain in Southeast Asia
(2007-01-01)
Maruyama, T.
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Kawamura, M.
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Saito, S.
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Nozaki, K.
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Kato, H.
An ionosonde network consisting of a meridional chain and an equatorial pair was established in the Southeast Asian area. Three of four ionosondes are along the magnetic meridian of 100° E; two are close to the magnetic conjugate points in Northern Thailand and West Sumatra, Indonesia, and the other is near the magnetic equator in the Malay Peninsula, Thailand. The fourth ionosonde is also near the magnetic equator in Vietnam but separated by about 6.3° towards east from the meridional chain. For a preliminary data analysis, nighttime ionospheric height variations at the three stations of the meridional chain were examined. The results demonstrate that the coordination of the network has a great potential for studying ionosphere/thermosphere dynamics. Through the assistance of model calculations, thermospheric neutral winds were inferred and compared with the HWM93 empirical thermospheric wind model. Higher-order wind variations that are not represented in the empirical model were found.
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The analysis of ionospheric scintillation on the global Positioning System (GPS) at Bangkok
(2006-12-01)
Theerapatpaiboon, P.
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Supnithi, P.
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Leelaruji, N.
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Hemmakorn, N.
This paper presents analysis of ionospheric scintillation on GPS signal (1575.45 MHz) by using the GSV4000 GPS receiver installed at KMITL. The characteristic of ionospheric scintillation on GPS signal are analyzed by employing S<inf>4</inf> index to identify the amplitude scintillation and σ<inf>ø</inf>(60 sec) to identify the phase scintillation, From the results, we found that the ionospheric scintillation phenomena impact on the GPS signal leading to the error in the global positioning system, differ from the non-scintillation period more than 20 meters. © 2006 ICASE.
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GPS detection of total electron content variations over Indonesia and Thailand following the 26 December 2004 earthquake
(2006-08-01)
Otsuka, Y.
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Kotake, N.
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Tsugawa, T.
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Shiokawa, K.
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Ogawa, T.
We report the response of the ionosphere to the large earthquake that occurred in West Sumatra, Indonesia, at 0058 UT on December 26, 2004. We have analyzed Global Positioning System (GPS) data obtained at two sites in Sumatra and at three sites in Thailand to investigate total electron content (TEC) variations. Between 14 and 40 min after the earthquake, TEC enhancements of 1.6-6.9 TEC units (TECU) were observed at subionospheric points located 360-2000 km north of the epicenter. From the time delays of the observed TEC enhancements, we find that the TEC enhancements propagated northward from the epicenter. The time delays between the earthquake and rapid increases in TEC, which occurred near the epicenter, are consistent with the idea that acoustic waves generated by the earthquake propagated into the ionosphere at the speed of sound to cause the TEC variations. A small TEC enhancement of 0.6 TECU was observed south of the epicenter, while no TEC enhancements were seen east of the epicenter. From a model calculation, we find that this directivity of the TEC variations with respect to the azimuth from the epicenter could be caused partially by the directivity in the response of the electron density variation to the acoustic waves in the neutral atmosphere. © 2006, The Seismological Society of Japan, Society of Geomagnetism and Earth, Planetary and Space Sciences, The Volcanological Society of Japan, The Geodetic Society of Japan, The Japanese Society for Planetary Sciences. All rights reserved.
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The effects of sumatra-andaman earthquake on total ionospheric electron content (TEC) and ionospheric scintillation of GPS signal in thailand
(2005-12-01)
Theerapatpaiboon, P.
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Leelaruji, N.
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Hemmakorn, N.
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Supnithi, P.
This paper presents the effects of Sumatra-Andaman earthquake (26 December 2004) on the total ionospheric electron content (TEC) by using the TEC Meter (JAVAD) installed at KMITL. From the results, we found that the total ionospheric electron content enhancement at the time of this earthquake is higher than other days about 7 TEC units. Furthermore, the study includes the effect of this phenomenon on GPS signal (1575.45 MHz) by employing S<inf>4</inf> index and σ<inf>φ</inf> (60sec) to identify the severity of amplitude scintillation and phase scintillation, respectively. From the observation, we can conclude that TEC variation is the cause of ionospheric scintillation leading to the position error on GPS about 8 meters. © 2005 IEEE.
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Rain attenuation of satellite link in Ku-band at Bangkok
(2005-12-01)
Boonchuk, T.
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Hemmakorn, N.
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Supnithi, P.
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Iida, M.
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Tanaka, K.
Rain attenuation is a major factor to degrade the system performance in a frequency above 10 GHz. This paper presents a statistical analysis of the rainfall rate and the rain attenuation data on satellite to ground propagation path. By measuring 12.7-GHz beacon signal attenuation from JCSAT satellite and the rainfall rate continuously. Yearly cumulative distribution functions were then compared to predicted models. The Crane Global model for the rain zone H provides overestimated predicted values to the measured ones. For the rain zone G, the Crane Global model provides close values to ITU-R model; both are smaller than the measured ones. © 2005 IEEE.
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Ka-band rain attenuation by radiometer method
(2003-01-01)
Nukfron, E.
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Boonchank, T.
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Decharat, A.
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Hemmakorn, N.
This paper would focus on investigating signal attenuation of Ka-band at zone N by using radiometer method and finally analyses the collective data by new developing indirect equation is ratiometer equation. According to equation analysis, the signal attenuation of Ka-band frequency depends on the differentiation of noise signal between clear sky condition and rain condition. Consequently, increasing of noise signal level is the result from rain cloud absorbing and discharging. The experiment site in this article was located at King Mongkut's Institute of Technology (KMITL) LadKrabang, Bangkok, Thailand (latitude 108E° and longitude 13.7N°) which represent for the tropical zone site. During 12 months of experiment period from May 2001 to April 2002, the results reveals clearly that the signal attenuation of Ka-band frequency are divided into 3 stages as follow: Stage I: signal attenuation before raining which is affect from rain cloud; Stage II: signal attenuation in raining period which is affect from rain; Stage III: signal attenuation after raining which is affect from high humidity. Finally, this paper will present worst month and lowest month in cumulative attenuation.
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Blocking probability of the reverse link cellular CDMA system
(2002-01-01)
Kumpairee, C.
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Kimpan, C.
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Pin-Ngern, O.
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Hemmakorn, N.
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Noppanakeepong, S.
The blocking probability of the reverse link cellular CDMA system is presented. Gaussian and lognormal approximation are the methods for determination of blocking probability. In the analysis in this paper, the parameter for the number of resolvable paths over a Rayleigh multipath fading channel is presented. In addition, we also show the effect of power control errors.

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