Continuous GPS receiver network inVietnam and application for theionospheric total electron content
study in Southeast Asian region
LE HUY MINH1, C. AMORY-MAZAUDIER2, R. FLEURY3,A. BOURDILLON4, P. LASSUDRIE-DUCHESNE3, TRAN THI LAN1,NGUYEN CHIEN THANG1 AND NGUYEN HA THANH1
1Institute of Geophysics, VAST,
2Laboratoire de Physique de Plasma, CNRS, France
3Bretagne Telecom, French
4Universitty of Rennes 1, French

3th AOSWA
Japan, March 2015

Outline* Continuous GPS stations in Vietnam andSoutheast Asian resion.
* Calculation of the TEC* Time variations of the crests of EIA* Main Remarks

Continuous GPSstations in Vietnam
4 GSV4004 receivers at
Phu Thuy, Hue,
Ho Chi Minh city,since 2005; (IGP-CNRS)
Bac Lieu: May 2014
(IGP-NICT)SMAV, SLAV, TGIV
DBIV, MLAY, MTEV,
Since 2010, Trimble NETRS,(IGP-NTU)

Vinh, since Sep. 2011,Trimble 5700 (IGP)a Lat, since October 2014
Javad, Multi-GNSS(IGP-JAXA)GPS Receiver in Hanoi, Hue and HOCM: GSV4004 model

Some other stations: Trimble 5700 CORS systems orTrimble NetRS GPS receivers

Multi-GNSS receiverat Da Lat observatory

JAVAD DELTA G3T: GPS, GLONASS, GALILEO, …

Continuous GPS stations in theSoutheast Asia region
nearly along 105o longitude
IGS: KUNM, NTUS, BAKO
SAMP, MNKL, XMIS

Magnetic equator (at about 7-8olatitude) nearly parallelto the geographic equator.

Calculation of the GPS Total Electron Contentiiiii
ττ()
p1i j = s0i j + d ion+d+c−+d+d+dtropjjq1q1 jresj
1jiiiii(ττ)
p2i j = s0i j + d ion+d+c−+d+d+dtropj
jq2
q2 j
resj
2j

i: satellite ; j: receiver, f1 = 1575.42 MHz, f2= 1227.60 MHz
p1, p2: pseudoranges for frequencies f1 and f2
s0: true distance between receiver and satellitedion, dtrop: the ionospheric and tropospheric effects
c: the speed of light in free space; τ: satellite or receiver clock offset
dq: instrument bias of satellite or receiver; dres: other bias
Tx

Tx

40,3
40,3
1 d ion = s − s0 = ∫  − 1dl = 2 ∫ Ndl = 2 TECn f RxfRx l1  f 12 f 22  iii 2(ppk
TEC =−−−kj)2j1j2 40,3  f 1 − f 2 ki = diq2 – diq1: : Satellite instrument bias
kj = dq2j – dq1j : Receiver instrument bias

Calculation of vertical ionospheric total electron content
Model of the single-layer ionospherez : Zenithal angle at theGPS receiver locationz’ : zenithal angle atthe ionospheric point

VTEC = TEC * cosz’
TEC : slant ionospheric total electron content
VTEC: Vertical TEC
Re = 6371.2 km (Earth’s rayon); hion = 400 km

Calculation of vertical ionospheric total electron content

Given ki+kj = 0, calculate the TECV0
By comparision between TECV0 and TECV fromglobal TEC model  (ki+kj) for each day.
Using the median value of (ki+kj) values in one monthas (ki+kj) for the month.

TEC in Hanoi, Hue and HOCM
April 2010

Diurnal variationof the TEC observed at
KUNM, PHUT, HUE,HOCM, NTUS andBAKO
on January 07, 2010
Shape of the diurnal
variation of TEC
depends on the latitude:a plateau at the stations
near equator: HOCM,NTUS; a Gaussian at theStations distant fromthe equator: KUNM,PHUT, BAKO.
UT = LT-7

Satellite foot prints
on the subionosphereobserved by the GPS
receivers in theSoutheast Asian region
on the April 12, 2006

Time and latitudinal monthly average TEC map for the 2006-2011 period

2006

2007

Equatorial ionization anomaly: two crests in two hemispheres, trough on the magnetic equator

2008

2009

2010

2011

2012

2013

Sunspot number and Magnitude of monthly anomaly crests(blue – northern crest, red – southern one) in the 2006-2013 period
R (SSN-TEC): ~ 0.88

12-month runningaverages : 0.98

Amplitude of TEC crests
in December greater thanin July This is thewinter anomaly for
Northern hemisphere,
but not in Southernone.

Solid lines: 12-month running averages

LATITUDE and OCCURRENCE TIME OF THE MONTHLY ANOMALY CRESTS

Solide lines: Averages

Both crests moveequatoward in winterthan other seasons.
There is tendency
for both crests toappear ealier inwinter and latterin summer.

Difference between the occurrence times of the Northern andSouthern monthly anomaly crests for the 2006-2013 periodMain Remarks• The GPS receiver chain near the 105°E longitude,including the Vietnamese stations and some ones fromadjacent countries, is very good for the studies of the TEC
variation in the Equatorial ionization anomaly in theSoutheast Asian region.
• The shape of the mean diurnal variation of TEC in theregion depends on the latitude: a plateau is observed at thestations near magnetic equator and a Gaussian at thestations near EIA crests distant from the equator• A semiannual pattern in all the stations with maxima atequinox. In both hemispheres, the amplitude of the crest islarger in spring than autumn from 2006 to 2008 andsmaller in spring than in autumn from 2009 to 2013.

Main remarks• A very high level correlation between the amplitudeof the TEC at two crests and the sunspot number:~0.88.
• During the deep solar minimum 2008-2009, theamplitude of crests of ionization becomes small
during several months in summer and winter.
• Both crests move significaltly equatorward in winterthan other seasons and there is a tendency for both
crests to appear earlier in winter and latter insummer.

Publication• M. Le Huy et al., 2014. Time variations ofthe total electron content in the Southeast
Asian equatorial ionization anomaly for theperiod 2006-2011, Advances in Space
Research, 54, 355-368.

Thank you for your attentions !