Current status and recent progress ofNICT’s ionospheric observations in theSoutheast Asia by GNSS-TEC and SEALION
Takuya Tsugawa1, Michi Nishioka1, Hiromitsu Ishibashi1, Takashi Maruyama1,Pornchai Supnithi2, Buldan Muslim3, Akinori Saito4, Yuichi Otsuka5,Mamoru Yamamoto6, Tsutomu Nagatsuma1, and Ken T. Murata1
1. National Institute of Information and Communications Technology (NICT), Japan
2. King Mongkut's Institute of Technology Ladkrabang (KMITL), Thailand
3. National Institute of Aeronautics and Space (LAPAN), Indonesia
4. Department of Geophysics, Graduate School of Science, Kyoto University, Japan
5. Solar-Terrestrial Environment Laboratory, Nagoya University, Japan
6. Research Institute for Sustainable Humanosphere, Kyoto University, Japan

Ionospheric effects on radio applications

GPS loss of lock caused by plasma bubble
Absolute TEC

12:20 UT
(21:20 JST)

12:40 UT
(21:40 JST)

13:00 UT
(22:00 JST)ROTI (~10km scaleirregularity)

Loss-of-Lock (~100mscale irregularity)

Plasma Bubble

135.6nm airglow images observed by
TIMED/GUVI [Christensen et al., 2003]

Schematic picture of plasma bubbles• Plasma bubbles generally can develop and create instability in thelow-latitude ionosphere after the sunset.
• Plasma bubbles generally drift eastward and have the structure
extending along the magnetic field line.
• A prompt penetrating magnetospheric electric field during themagnetic storm helped to trigger the super plasma bubble observedat mid-latitudes.

Realtime TEC observation in Japan
NICT started realtime (now 10-30 min delay) two-dimensional TEC
observation using realtime GEONET data in the collaboration with ENRI,
Kyoto-U., and Nagoya-U.
http://seg-web.nict.go.jp/GPS/RT_GEONETCurrent status of SEALION(SouthEast Asia Low-latitude IOnospheric Network)

SEALION is a joint project among the following institutions and countries:• National Institute of Information and Communications Technology (NICT), Japan• King Mongkut's Institute of Technology Ladkrabang (KMITL), Thailand• Chiang Mai University (CMU), Thailand• National Institute of Aeronautics and Space (LAPAN), Indonesia• Hanoi Institute of Geophysics (HIG), Vietnamese Academy of Science and Technology, Vietnam• Center for Space Science and Applied Research (CSSAR), Chinese Academy of Sciences, China• University of San Carlos (USC), Philippines• Kyoto University, Japan

GPS receiver networks in Southeast Asia

HF Transequatorial Propagation(HF-TEP) Experiments

Azimuthdirection ofequatorialterminator

Eastward
propagation

Eastward
propagation

plasmabubble

1218

24
LT, hr06[Maruyama and Kawamura, AG, 2006]

12

GNSS Receiver Networks

As of Jan 2010, we are collecting all the available GNSS receiver data
(more than 5,000 receivers) which belong to GEONET, UNAVCO, SOPAC,IGS, CORS, EPN, etc.
We have developed regional/global high-resolution maps of absolute TEC,
detrended TEC, ROTI, loss-of-lock on GPS signals.

Some results of SEALION and GNSS-TEC observations
h’F(KTB)-h’F(CMU) (km)Latitudinal profile of absolute TEC during 2006-2010
60
40
200-20-40 October 2004 andMarch-April 2005
-60
182022Local Time

0002

Differences between h'F observed
at Kototabang and Chiang Mai. [Saito andMaruyama, 2006]

Plasma bubble

No Plasma bubble

Latitudinal profiles of daily average of TEC along
100 deg E longitude during 2006-2010 for plasma
bubble (left) and no plasma bubble observed
days. [Courtesy of Dr. M. Nishioka (NICT)]• North-south asymmetry of plasma density structure suppresses theplasma bubble [Saito and Maruyama, 2006]• EIA is developed even in the nighttime for post-sunset plasma bubbleobserved days.
• EIA is very weak or negligible for no plasma bubble observed days.

Some results of SEALION and GNSS-TEC observations

Contour plot of the EEJ ground strength during
the period from November 2007 to October 2008.
[Uemoto et al., 2010]• The h’F and ESF onsets at Chumphon
were compared with EEJ ground strength
at Phuket during Nov. 2007 – Oct. 2008.
• Increase in the F-layer height and ESFonsets during the evening hours were wellconnected with the EEJ ground strength
before sunset.
• E-region dynamo current and/or electricfield are related to the F-region dynamics
and ESF onsets around sunset.

Dependence of the ESF occurrences on the peakh’F of PRE (a), daytime (b) and pre-sunset IEEJ
(c). Solid and open bars indicate the ratios of ESF
and no ESF days to the total number of days
contained in each bin. The total number of days ineach bin is given on the top of each bar.
[Uemoto et al., 2010]

Southeast Asian GPS Networks
Available for Ionospheric Researches
PresentNear Future Image

TID?
EIA?

TID
EAI

Plasma Bubble?

EIA?
TID?

Plasma Bubble

EAITID• Dense and wide-coverage GPS receiver network can reveal their spatial structures,propagation directions, and temporal evolutions.
• The GPS-TEC maps greatly contribute to the ionospheric researches and thenowcast/forecast of space weather.
• However, it is difficult to collect or share the GNSS data in some countries.

General GPS-TEC data (ex. IONEX)Multi GPS Receivers

RINEX Navigation

RINEX Observation DataData

Input

Satellite/receiver biases, absoluteslant TEC estimation
Slant-to-vertical TEC conversion

Satellite Biases

Receiver Biases

OutputAbsolute VTEC Map Data
• Vertical absolute TEC (VTEC) map data and instrumental biases
of satellite and receiver are simultaneously derived from multi
GPS receiver data and satellite orbit data.
• Temporal and spatial resolution of VTEC Map data are too low toobserve small-scale ionospheric disturbances such as plasma
bubble and ionospheric waves.

Proposed GNSS-TEC data for data sharing
Input

OutputIGS Orbit Data

Single GPS Receiver
RINEX Observation Data

Slant TEC derivation

Combined satellite
and receiverbiases estimation

Slant TEC with Biases

Combined Biases

Biases subtraction

High-pass filter
Slant-to-vertical
TEC conversion
Multiple receiverdata processing

Absolute Slant TEC
IGS Orbit Data

VTEC perturbation Map Data

Slant-to-vertical
TEC conversion
Multiple receiverdata processing• Slant TEC data
including satellite andreceiver biases arederived from GPSdata of one receiver.
• VTEC maps can bederived using theslant TEC data frommulti GPS receivers.

• The VTEC data canhave high temporaland spatial resolution.
• The Slant TEC data
would be suitable fordata sharing in theSoutheast Asia.
Absolute VTEC Map Data

GNSS-TEC exchange (GTEX) format

GNSS-TEC data sharing based on GTEX• NICT have developed the database of“GTEX” data for more than 6,000 GNSS
receivers in the world. These data are
available via the NICT science cloud,OneSpaceNet (OSN):• Since the 1st AOSWA workshop held inChiang Mai, Thailand in February 2012,
we are now developing the GTEX dataof Thailand, Indonesia, South Korea, anChina collaborated with KMITL, LAPAN,KMA, and CMA, respectively.

Detrended TEC overThailand. [Courtesy ofK. Watthanasangmechai(KMITL)]

Detrended TEC overIndonesia by SUGAR
network.

• We can provide softwares toconvert RINEX data to GTEX
data (Fortran 77) , and to makehigh-resolution TEC maps (IDL).
• NICT recently released aWindows software “RNX2GTEX”
which are available via the NICT
website:http://seg-web.nict.go.jp/e-sw/download/index_e.html

Summary• Current status and recent progress of GNSS-TEC and SEALION
observations in the Southeast Asia are introduced.

• These data have been used for monitoring and researching severe
ionospheric disturbances which can degrade GNSS navigations andcause loss-of-lock on GNSS signals.
• The dense GNSS receiver networks in the Asia-Oceania region
would be a powerful tool for the nowcast/forecast of ionosphericdisturbances such as plasma bubbles.

• We have developed GNSS-TEC data sharing system based on“GTEX” collaborated with LAPAN, KMITL, KMA, and CMA. A
Windows software “RNX2GTEX” are now available.

Acknowledgement
GNSS receiver data are provided by GSI, UNAVCO, IGS, SOPAC, CORS, WCDA,CHAIN, PANGA, KASI, EPN, BKGE, OLG, IGNE, DUT, ASI, ITACyL, ESEAS,SWEPOS, SATREF, BIGF, TrigNet, Geoscience Australia, IPS, RBMC, SUGAR, DPT,and KMITL.