# Presentation: 947560

## Status of the IGS ionosphere products & future developments 

**Manuel Hernandez-Pajares**** **

**(****Technical University of Catalonia, Spain****)**** **

**Andrzej Krankowski **

**(****University of Warmia and Mazury in Olsztyn, Poland****)**** **

**and**** **

## Outline

**Introduction**

**IGS IONO WG activities**

**Summary of IGS global TEC maps performance**

**Future activities and Conclusions**

## International GPS Service, IGS

**International GPS Service, IGS**

**IGS directly manages more than about 350 permanent GPS stations, observing some 4-1****2**** satellites at 30 sec rate: more than 250,000 STEC worldwide** **observations/hour, but there is  lack of stations at the South and over the Seas**

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

- 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.

## Computing Global VTEC maps: layout

**GPS raw data**

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

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

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

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

**(5) Computing the Interfrequency Delay Code Biases**

## VTEC global maps: the cooperative effort in IGS

**IGS****GPS data**

**IGS****Ionosphere Analysis Centers**

**IGS****Ionosphere Validation Centers**

**IGS****Ionosphere Combination****Center**

**IGS****Ionosphere**

- 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).

- 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.

## IGS Final Ionosphere Flow-Chart

**GPS****rec.1**

**GPS****rec.N**

**IGS****server**

**CODE****iono.**

**ESA****iono.**

**JPL****iono.**

**UPC****iono.**

**NRCan****iono*******

**NRCan*********weights**

**UPC****weights**

**JPL****JASON ****TEC**

**U****WM****comb.**

**...**

**U****WM****server**

**IGS****server**

**IGS ****Iono.**

**JASON obs.**

**IGS Iono.****Ext.valid.**

**IGS****Ionosphere Analysis Centers**

**IGS****Ionosphere Validation Centers**

**IGS****Ionosphere Combination****Center**

- * NRCan has stopped temporarily the ionospheric production

**ESA****ENVISAT ****TEC**

**ENVISAT**** obs.**

## The transition process in 

**IGS Ionospheric Working Group**

** ****In previous year, 2007, the IGS Ionospheric Product  **
**   ****Coordinat****or**** (****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.**

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

**Units: 0.1 TECUs**

- 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.

- 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.

## 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.

## Overall validation of VTEC maps during more than 9 years of IGS final VTEC maps

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

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

**01-03UT**

**07-09UT**

**13-15UT**

**19-21UT**

**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).

## 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 (>30 000 000 observations)

**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 (****>****30**** ****000**** ****000 observations)**

**IGSG**** **

**COD****G**** **

**JPL****G**** **

**ESA****G**** **

**UPC****G**** **

## Rapid vs Final IGS DCBs

**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)

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

**Global Electron Content Unit (GECU) defined as 10****32**** electron****s**

**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).**

## Comparison of recent Global Ionosphere maps

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

- 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/](ftp://cddisa.gsfc.nasa.gov/gps/products/ionex/)_
**IGS Ionosphere WG download links** at : _[http://gage152.upc.es/~ionex3/igs_iono/igs_iono.html](http://gage152.upc.es/~ionex3/igs_iono/igs_iono.html)_
- _ftp://_**igs-rapid.man.olsztyn.pl****/rapid_iono_igs/**

**Comparison of recent Global Ionosphere maps**

## IGS IONEX usage statistics for both 

**IGS IONEX usage statistics for both **
**final(IGSG) and rapid (IGRG) VTEC maps**

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

## 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****.**

## 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

**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**** (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).**

**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)**

**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.**

**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.**

**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**

## Conclusions

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

**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****.**

**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**