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Status of the IGS ionosphere products & future developments. Andrzej Krankowski. ( University of Warmia and Mazury in Olsztyn, Poland ). and. Manuel Hernandez-Pajares. ( Technical University of Catalonia, Spain ). Outline. Introduction. IGS IONO WG activities.

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slide1

Status of the IGS ionosphere products & future developments

Andrzej Krankowski

(University of Warmia and Mazury in Olsztyn, Poland)

and

Manuel Hernandez-Pajares

(Technical University of Catalonia, Spain)

slide2

Outline

Introduction

IGS IONO WG activities

Summary of IGS global TEC maps performance

Future activities and Conclusions

slide3

International GPS Service, IGS

IGS directly manages more than about 350 permanent GPS stations, observing some 4-12 satellites at 30 sec rate: more than 250,000 STEC worldwideobservations/hour, but there is lack of stations at the South and over the Seas

slide4

Determining VTEC in a global network: main problem of lack of data in South and Seas

  • Lack of data in equatorial Africa and Atlantic, and in part of equatorial and southern Pacific, hamper the detection of the equatorial anomalies (June 13, 2004).
  • It can be seen the typical “holes” appearing in the first stage of the global maps computation (each 2 hours). This requires an optimum spatial-temporal interpolation technique to extend the estimates covering all the Ionosphere.
slide5

Computing Global VTEC maps: layout

Kalman Filter

GPS raw data

(1) Preprocessing: cycle-slips, satellite pos., antenna phase centers,…

(2) STEC estimation (i.e. L1-L2 bias estimation)

(5) Computing the Interfrequency Delay Code Biases

(3) VTEC estimation over the GPS stations (i.e. deprojecting STEC)

(4) VTEC interpolation (i.e. “filling the gaps”)

slide6

VTEC global maps: the cooperative effort in IGS

The IGS Ionosphere Working group started its activities in June 1998 with the main goal of a routinely producing IGS Global TEC maps (IGTEC). This is being done now with a latency of 11 days (final product) and with a latency of less than 24 hours (rapid product).

IGSGPS data

IGSIonosphere Analysis Centers

IGSIonosphere Validation Centers

IGSIonosphere

IGSIonosphere CombinationCenter

The IGS ionosphere product is a result of the combination of different Analysis Centers TEC maps by using weights computed from GPS data by Validation Centers, in order to get a more accurate product.

slide7

IGS Final Ionosphere Flow-Chart

GPSrec.1

GPSrec.N

ENVISAT obs.

IGSIonosphere Analysis Centers

IGSserver

JASON obs.

CODEiono.

ESAiono.

JPLiono.

NRCaniono*

UPCiono.

NRCan*weights

IGSIonosphere CombinationCenter

ESAENVISAT TEC

IGSserver

UPCweights

UWMcomb.

JPLJASON TEC

UWMserver

IGSIonosphere Validation Centers

IGS Iono.

IGS Iono.Ext.valid.

* NRCan has stopped temporarily the ionospheric production

slide8

The transition process in

IGS Ionospheric Working Group

  • In previous year, 2007, the IGS Ionospheric Product

Coordinator (IPC) and IGS Ionospheric Working Group

Chairman (IWC) duties was split between Andrzej

Krankowski (from University of Warmia and Mazury in

Olsztyn, Poland) and Manuel Hernandez-Pajares

(from Technical University of Catalonia, Spain),

respectively.

  • Since this year, after the transition period and after IGS

Governing Board and Iono WG approval, Manuel

Hernandez-Pajares passed the IGS Iono WG Chairmanship

to Andrzej Krankowski as well.

slide9

Example of IGS Final TEC map: 2003-347-00UT

Five Analysis Centers (CODE, ESA, JPL, NRCan and UPC) and 4 Validation Centers (JPL, ESA, NRCan and UPC) have been providing maps (at 2 hours x 5 deg. x 2.5 deg in UT x Lon. x Lat.), weights and external (dual-frequency altimetry-derived) TEC data.

Units: 0.1 TECUs

From such maps and weights the corresponding combination center (firstly ESA, and secondly UPC since Dec.2002) and recently UWM (since January, 2008) has produced the IGS TEC maps in ionex format.

slide10

The IONEX format body

1 START OF TEC MAP

2004 4 27 0 0 0 EPOCH OF CURRENT MAP

87.5-180.0 180.0 5.0 450.0 LAT/LON1/LON2/DLON/H

123 123 123 124 125 125 126 126 126 126 126 126 125 125 125 128

125 125 125 126 126 125 124 124 124 124 124 123 123 122 122 121

120 120 119 118 118 118 118 118 117 117 116 116 115 114 114 113

113 113 114 114 114 114 115 115 115 116 116 117 117 118 119 120

120 121 121 122 123 123 123 123 123

85.0-180.0 180.0 5.0 450.0 LAT/LON1/LON2/DLON/H

129 129 130 131 132 132 133 133 134 134 134 134 134 134 134 136

135 136 130 129 129 129 128 128 128 127 126 124 123 122 121 120

119 118 117 117 117 117 116 116 115 115 114 113 112 111 110 109

109 110 109 109 109 110 111 111 112 112 113 113 115 116 117 118

120 122 123 125 126 127 128 129 129

...

-87.5-180.0 180.0 5.0 450.0 LAT/LON1/LON2/DLON/H

87 88 88 90 90 91 92 93 93 94 94 95 94 93 91 89

87 86 85 84 83 82 81 81 80 80 79 78 78 78 77 77

76 76 76 75 75 76 77 77 76 79 79 79 80 81 82 83

83 84 85 85 85 85 85 85 85 86 87 87 87 88 88 87

87 87 87 88 87 87 87 87 87

1 END OF TEC MAP

2 START OF TEC MAP

...

...

13 END OF TEC MAP

1 START OF RMS MAP

2004 4 27 0 0 0 EPOCH OF CURRENT MAP

87.5-180.0 180.0 5.0 450.0 LAT/LON1/LON2/DLON/H

7 7 7 7 7 7 7 7 7 7 8 8 9 9 9 6

8 8 8 6 6 7 7 7 7 6 6 6 6 6 6 6

6 6 7 7 7 6 7 6 6 7 7 7 7 8 8 9

10 9 8 8 8 8 7 7 8 8 8 8 7 7 7 7

7 6 6 7 6 7 6 6 7

...

13 END OF RMS MAP

END OF FILE

The IONEX (IONosphere interEXchange) format allows to store the VTEC and its error estimates in a grid format, in consecutive values –at different longitudes- for each latitude grid point.

slide12

Example of comparison of IGS vs JASON: 2003-347 each 6 hours

01-03UT

07-09UT

Units: approx. 10 TECUs

Red: Jason-1 TEC

Green: IGS final TEC

JASON dual frequency altimeter provides a direct and independent VTEC below its orbit (1300 km) and over the oceans (worst case for GPS).

13-15UT

19-21UT

slide13

CODG

JPLG

IGSG

ESAG

Cumulative Distribution Function of VTEC discrepancy values provided by final VTEC maps (vertical axis) regarding to the VTEC values, directly observed by the TOPEX/JASON altimeters (horizontal axis), during the period day 349 2002 to end of 2007 (>30000000 observations)

UPCG

slide14

Rapid vs Final IGS DCBs

Rapid IGS DCBs are typically in agreement with the Final ones at the level of its repeatability(less than 0.1 ns for the Satellite DCBs and less than 1 ns for the receiver DCBs)

slide15

Evolution of Global Electron Content during more than 9 years of IGS final VTEC maps

Global Electron Content Unit (GECU) defined as 1032 electrons

Global Electron Content evolution during the availability of IGS Ionospheric products, since 1st June 1998

(source: Final IGS VTEC maps).

Global Electron Content evolution during the availability of IGS Ionospheric products, vs. Solar Flux, Ap index and Xray flux, since 1st June 1998

(source: Final IGS VTEC maps).

slide16

Yesterday’s Ionosphere (day 173, 2004, mid-low part of Solar Cycle).

Comparison of recent Global Ionosphere maps

Spring eq. Ionosphere (day 80, 2004).

Spring around the Solar Max (day 80, 2002).

IGS Final Ionosphere ionex files at ftp://cddisa.gsfc.nasa.gov/gps/products/ionex/

IGS Ionosphere WG download links at : http://gage152.upc.es/~ionex3/igs_iono/igs_iono.html

ftp://igs-rapid.man.olsztyn.pl/rapid_iono_igs/

slide17

IGS IONEX usage statistics for both

final(IGSG) and rapid (IGRG) VTEC maps

downloads from main server only - cddis.gsfc.nasa.gov

slide18

Future plans of IGS IWG and Conclusions

The following actions may be considered:

- Agreement between IGS and the ESA SMOS project,

-Higher temporal resolution, e.g. 1 hour (some AAC’s already produced TEC maps with even 15-minute interval),

  • A simple method to apply the second order ionospheric
  • correction has been proposed by the Iono WG, as a result
  • of the action item proposed at IGS 2004 Technical meeting
  • held in Bern.
slide19

Agreement between the International GNSS Service

(IGS) and the ESA SMOS project

  • The Soil Moisture and Ocean Salinity (SMOS) mission is part of the Earth Explorer programme of the European Space Agency (ESA).
  • The launch of SMOS is currently planned for November 2008.
  • The SMOS project requests the support of the IGS over a period of nominally 7 years (the expected operational lifetime of the SMOS spacecraft).
  • Required are global maps of Vertical Total Electron Content (VTEC).
i2 effects on subdaily differential estimation
I2 effects on subdaily differential estimation

Coordinates (north shift of AOML): Small efect (up to ~1mm) and NO significant dependence on I2 at reference stat. The small observed effect depend on the relative I2 value, regarding to the reference station (I2-I2ref).

Satellite clock effect: significant (up to +2cm) and dependent on I2 at reference station

Carrier phase bias effect: significant (up to +4cm) and dependent on I2

Coordinates: A negative I2-I2ref produces an increase of range, and a corresponding increase of north (instead of southward) and up component, up to 1mm, in a northern hemisphere station.

mean i2 effect on receiver positions 21 months 2002 03
Mean I2 effect on receiver positions (21 months, 2002 -03)

Results are not equivalent to those obtained by previous authors: Among I2 processing complete for all the geodetic parameters, more realistic magnetic field model (see below) and more homogeneous distribution of receivers are some of the hints to explain this.

Receiver position effect: Confirming previous results with differential scenario, the dependence on the difference of I2 values wrt neighbor receivers, producing long term effects at mm level and few tenths of mm for daily repeatability effect.

Hernández-Pajares, M., J.M.Juan, J.Sanz and R.Orús, Second-order ionospheric term in GPS: Implementation and impact on geodetic estimates, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, B08417, doi:10.1029/2006JB004707, 2007

slide22

Conclusions

Future improvements are determined by the users requirements (the number of users has significantly increased during the last years).

A good example is the recent interest of SMOS ESA mission on using the IGS VTEC maps, including predicted products.

Long series of IGS VTEC maps offers a very good source with high both spatial and temporal resolution, to get significant spectral results.

A long time series of accurate global VTEC values are available since 1998, which are freely available for scientific or technical usage, with latencies of about 12 days (final product) or >1-2 days (rapid product). Thanks to the cooperative effort developed within the IGS framework and the international scientific community this open service will hopefully continue its evolution during the next years, sensitive to both new user needs and scientific achievements.

Hernández-Pajares, M., J.M.Juan, J.Sanz, R.Orús,A. Garcia-Rigo,

J.Feltens A. Komjathy, S.C. Schaer, A.Krankowski, The IGS VTEC maps: A reliable source of ionospheric information since 1998, submitted to Journal of Geodesy