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The GBAS protection levels and availability during ionospheric irregularity occurrence
(2016-09-06)
Limjumroonrat, Chayanan
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Rungraengwajiake, Sarawoot
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Supnihi, Pornchai
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Supanunt, Wisanu
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Siansawasdi, Nattapong
The next generation aeronautical navigation system utilizes the Global navigation satellite system (GNSS) based equipment to aid aircrafts during approaching and landing. The Ground-based augmentation system (GBAS) broadcasts the augmentation information to the aircrafts in order to compensate for the GNSS signal-in-space errors and provides the accuracy, integrity, continuity and availability of system. The protection level is a parameter in the Standards and Recommended Practices (SARPs) from the International Civil Aviation Organization (ICAO) GBAS standard which validates the availability of system. The ICAO SARPs's algorithms are applied in this paper to compute the GBAS protection levels. We use the GNSS data recorded at the Suvarnnahumi international airport (AERO) in 2014. The results show statistics of days with ionospheric irregularity in 2014 as well as the protection levels during ionospheric irregularity occurrences. The average of the availability in March (equinox) is 99.30% and July (solstice) is 99.93% at the altitude of 100 feet. But the average availability of September (equinox) is 99.98%. So, that will be another reason that reduce the availability unless the ionospheric irregularity.
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Ionospheric delay gradient monitoring for GBAS by GPS stations near Suvarnabhumi airport, Thailand
(2015-10-01)
Rungraengwajiake, Sarawoot
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Supnithi, Pornchai
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Saito, Susumu
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Siansawasdi, Nattapong
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Saekow, Apitep
Ground-based augmentation system (GBAS) is an important augmentation system that provides the differential corrections and integrity information from the reference stations to the aircrafts for precision approach and landing. It is known that the nonuniform ionospheric characteristics called "ionospheric delay gradient" can cause the errors in differential corrections degrading the accuracy and safety level if they are undetected by the reference stations. Since the characteristics of the ionosphere are different for each region, the ionospheric delay gradient observations in equatorial and low-latitude regions are necessary for developing the suitable ionospheric threat models. The purpose of this work is to analyze the ionospheric delay gradients observed by three GPS stations near Suvarnabhumi airport in Bangkok, Thailand, which is located in the low-latitude region. The ionospheric irregularities in this region are mainly caused by the plasma bubble, which usually occurs after sunset. The GPS data with plasma bubble occurrence during the September equinox 2011 and 2012 are therefore analyzed. In addition, the data analysis procedure utilizing the rate of total electron content change index for this region is proposed. The results show that the ionospheric delay gradients observed in the west-east direction appear higher than the south-north direction, varying from 28 to 178 mm/km during plasma bubble occurrences.
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The occurrence of equatorial spread-F at conjugate stations in Southeast Asia
(2015-04-15)
Klinngam, Somjai
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Supnithi, Pornchai
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Rungraengwajiake, Sarawoot
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Tsugawa, Takuya
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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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Drift velocity estimation of ionospheric disturbance using GPS observations
(2014-01-01)
Bumrungkit, Acharaporn
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Rungraengwajiake, Sarawoot
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Supnithi, Pornchai
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Siansawasdi, Nattapong
The Ground-Based Augmentation System (GBAS) based on the global positioning system (GPS) is used for positioning accuracy improvement of the aircraft landing. However, the ionospheric irregularity can cause irregular electron density that affects the accuracy of GBAS system. In this work, we analyze the drift velocity of ionospheric irregularity or plasma bubble phenomenon by using the correlation time of slant total electron content (STEC) from two GPS receivers that are located near Suvarnabhumi airport, Thailand. The data on September 1<sup>st</sup>, 2011 with the plasma bubble occurrence is analyzed. The result shows the drift velocity of plasma bubbles is about 108 meterspersecond (m/s). © 2014 IEEE.
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Study of ionospheric delay gradient based on GPS monitoring stations near Suvarnabhumi airport in Thailand
(2014-01-01)
Rungraengwajiake, Sarawoot
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Supnithi, Pornchai
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Saito, Susumu
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Siansawasdi, Nattapong
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Saekow, Apitep
The ionospheric delay gradient is an important parameter for the planning of ground-based augmentation system (GBAS) in a region. When it is beyond the limit, the integrity and safety for landing approach of CAT II/III may be compromised. In order to maintain the availability and safety requirement of the system, the ionospheric threat models have been developed in several countries during the past few years. However, the ionospheric delay gradient associated with plasma bubble in low latitude region has not been studied well. In this work, we present some analytical results of ionospheric delay gradient based on three GPS monitoring stations near Suvarnabhumi airport in Thailand. The stations are located on the campus of King Mongkut's Institute of Technology Ladkrabang (13.7278°N, 100.7726°E), Stamford University (13.7356°N, 100.6612°E) and Suvarnabhumi airport (13.6945°N, 100.7608°E). The analyzed results on 1st September 2011 show that the ionospheric delay gradient varies from -95.23 to 107.7 mm/km during the occurrence of the plasma bubbles. © 2014 Springer.
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The variation of equatorial spread-F occurrences observed by ionosondes at Thailand longitude sector
(2013-11-15)
Rungraengwajiake, Sarawoot
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Supnithi, Pornchai
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Tsugawa, Takuya
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Maruyama, Takashi
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Nagatsuma, Tsutomu
The equatorial spread-F (ESF) is a phenomenon of ionopheric irregularities which are mainly generated by the generalized Rayleigh-Taylor (R-T) instability mechanism in conjunction with the other physical mechanisms, originated at the bottom side of the F-layer in the equatorial region after sunset. It degrades the quality of signals that propagate through these irregularities, especially in the navigation satellite system, which requires the high integrity signals. In this work, we analyze the ESF statistics obtained from the FM/CW ionosonde stations over Thailand longitude sector. One is at Chumphon (10.72 N, 99.37 E, dip latitude 3.0), located near the geomagnetic equator, and the other station is located at Chiangmai (18.76 N, 98.93 E, dip latitude 12.7). Both stations are as part of the South-East Asia Low Latitude Ionospheric Network (SEALION) project. The ionograms are obtained at every 15 min from September 2004 to August 2005, which has the monthly mean of solar 10.7 cm flux (F10.7) from ∼80 to ∼110. In addition, we compare the diurnal patterns between the ESF occurrences and the variation of virtual height of the F-layer bottom side (h'F) of these two stations. The results show that the ESF occurrences at Chumphon stations are higher than Chiangmai station in all seasons. The high ESF occurrences of both stations mostly occur in equinoctial months corresponded with the rapid rising of the monthly mean h'F in the post-sunset. However, some inconsistent results are still observed, implying the role of other factors such as gravity waves and planetary waves to ESF occurrences. © 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.
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Loss-of-lock statistics from the GPS receiver near Suvarnabhumi airport, Thailand
(2011-10-03)
Le Hoai, Phong Pham
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Rungraengwajiake, Sarawoot
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Supnithi, Pornchai
Loss-of-lock (LOL) statistics are important to the study of the ionosphere and the availability of the GPS/GNSS technology. The LOL data of the GPS, for instance, together with the spread-F and the rate of TEC change index (ROTI) are often used to the study of plasma bubble occurrence in the low and equatorial latitudes. In our work, we collected the data from the GPS receiver near Suvarnabhumi airport, Thailand, in 2010 and investigated the LOL statistics during this time. The number of proposed parameters including the probability of visible GPS satellites with LOL, and the number of usable GPS satellites are used to evaluate the LOL statistics. A comparison of the probability of LOL on both GPS frequency carriers indicates that the L<inf>2</inf> frequency is more susceptible to the LOL events than L<inf>1</inf> frequency. The results also show that the dense LOL occurrence is related to high fluctuation ROTI. The inversely correlation between elevation angles and number of visible GPS satellites with LOL is obtained as well. © 2011 IEEE.

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