# Presentation: 576922

## International Association of Geodesy (IAG): GPS and GNSS for Science 

**G. Beutler**
*Astronomi**cal** Institut**e**, Universi**ty of** Bern*
***Member of****** IAG Executive Committee***
***and of******  IGS Governing Board***
**National Space-Based Positioning, Navigation, And Timing (PNT) Advisory Board**
**Hilton Arlington **
**901 North Stafford Street **
**Virginia 22203**** **
**October**** ****16-17****, 200****8**

## International Association of Geodesy (IAG): GPS and GNSS for Science

**The International Association of Geodesy (****IAG****)**
**Global Navigation Satellite Systems (****GNSS****)**
**The International GNSS Service (****IGS****)**
**Leadership**
**Strategic engagement**
**Future challenges**
**General remarks concerning the *****activities of the***** *****2007-2008 National Space-Based ******PNT Advisory Board****** *****from the IAG perspective**

## About Geodesy and IAG

**Geodesy**** is based on ****three pillars**
***geometry and kinematics ******of/******on Earth and in its environment,***
***Earth orientation and rotation*****, and **
***The Earth‘s gravity field including its variability***
***Geodesy provides the metrological basis for positioning, navigation, surveying&mapping, global change studies.****** ***
** ****IAG****, the ****International Association of Geodesy****, coordinates International activities related to the above pillars.**
**The space age brought a revolution in geodesy and led to the creation of four services relevant for GNSS,**
**International Earth Rotation Service (IERS) in 1989 **
**IGS**** (****International GNSS Service****) in 1991/1994**
** ****ILRS**** (Intl. Laser Ranging Service) and **
**IVS (Intl. VLBI Service) around the year 2000. **

## Active and Emerging GNSS

**In addition China is developing a global/regional system ****COMPASS ****with geostationary *****and***** MEO satellites.  **

## About Geodesy and IAG

**Since 1994 Global Navigation Satellite Systems (GNSS) play an essential role in geodesy to**** **
**maintain and densify the International Terrestrial ****Reference Frame**** (ITRF, issued by the IERS)**
**monitor ****Earth rotation**
**monitor the ****atmosphere**
**determine ****precise LEO orbits**** (LEO=Low Earth Orbiter)**
**determine the ****Earth‘s gravity field**** (!) **
**In geodesy GNSS will continue to play a leading role for next 20-30 years.**
**The ****IGS**** (International GNSS Service) is ****acting on behalf of IAG for the scientific exploitation of all GNSS.**

## About the IGS

**The creation of the IGS was ****initiated in Edinburgh in 1989**** with I.I. Mueller, G. Mader, B. Melbourne, and ****Ruth Neilan ****as protagonists**
**The IGS became an ****official IAG service**** in 1994.**
**The IGS first was a pure ****GPS Service****, it was renamed as the ****International GNSS Service**** in 2004.**
**Today, the IGS is a truly ****interdisciplinary service in support of Earth Sciences and Society**** committed to use the data from all GNSS.**
**Since its creation the ****IGS Central Bureau**** is located in the USA with ****Ruth Neilan**** as director – who stands for ****continuity**** and ****leadership****.**

## About the IGS

**In 1992 the IGS GPS network was based on a****bout 20**** geodetic ****receivers****, 400+ receivers are active and their data retrievable today**

**IGS Network in 2008**

**Monitor station motion in „real time“**

## About the IGS

**Development of the IGS combined GPS/GLONASS network (from Dach et al., 2008 IGS Workshop)**

## About the IGS

**In 1992 the IGS started off as an orbit determination service (decimeter accuracy) for about 20 GPS satellites.**
**Today,**** the IGS provides**** ****ephemerides**** (accuracy of 2-4 cm) for about ****30 GPS satellites**** and for all ****GLONASS satellites (<10 cm)****, i.e., ****for all currently active GNSS satellites****.**
**In addition the IGS provides**
**archive of all globally relevant GNSS observations since 1991 **
**satellite and receiver clock corrections**** (sub-ns accuracy) **
**polar motion (PM) and length of day (lod)**** (cm accuracy)**
**coordinates and velocities for 200+ sites**** (cm / mm/y accuracy)**
**atmosphere information**
**The IGS products are ****accurate****,**** reliable**** and ****robust****, available in a ****timely**** manner.  **

## About the IGS

**The IGS**** **
**provides leadership**** to the Civilian GPS/GNSS community striving for the highest achievable accuracy by studying**
**systematic errors (case for SLR reflectors)**
**system peculiarities (case of 30+ constellation)**
**different GNSS and their combination to the benefit of users**
**reaches out**** to the entire GNSS community by making available precise**
**GPS**
**GLONASS**
**in future hopefully also GALILEO**
**    ****orbits and clocks in one and the same reference frame.**
**identifies future challenges by its strategic planning**

## Case for SLR reflectors

-        above the orbital plane
- u ... Argument of latitude
-        (satellite – Sun)

**Case for SLR reflectors**

- Satellite‘s position w.r.t. the Sun

## Case for SLR reflectors

**Case for SLR reflectors**

- (cm)

- G05 + G06

## Case for SLR reflectors

**From:**** ****Yang Fumin(1), Chen Wanzhen(1), Zhang Zhongping(1),**** ****Wang Yuanming(1), Zhang Haifeng(1)**
**Zhao You(2), Fan Cunbo(2) and Han Xingwei(2)**
**(1) Shanghai Observatory, Chinese Academy of Sciences, Shanghai, China**
**(2) Changchun Observatory, Chinese Academy of Sciences, Changchun, China**

## SLR Reflectors on GNSS Satellites

**SLR provides the only independent check**** (in the radial direction) of ****GNSS orbits**** – determined with the GNSS signals and carriers.**
**The payload required to enable SLR tracking is minor (about 10 kg, the SLA on Compass has 2.5 kg), the costs marginal.**
**SLR tracking to GNSS, internationally coordinated by the ILRS, was successfully performed for **
**GPS (PRN 05 & 06)**
**All GLONASS satellites**
**GIOVE-A & -B (GALILEO)**
**COMPASS-M1 (launched in spring 2007)**

## GNSS Peculiarities

**The GNSS constellations differ considerably (inclinations, daily vs. 8-day repeat orbits for GPS and GLONASS, respectively) **
**Different constellations improve the geometry, help to understand systematic errors**

**July 7, 2006: ****sub-satellite tracks**** of: **
**GPS PRN 06,**** with daily repeat orbit and**
**GLONASS R06, ****orbit repeating after  8 days.**

## GNSS Peculiarities

**Observing GPS and GLONASS from one site: Mean inclinations of GPS and GLONASS ore different (Dach et al., 2008)**

## GNSS Peculiarities

**Observing one GPS and one GLONASS satellite over ten days from two different sites (roughly) at the same latitude (Dach et al., 2008) **

## Case for 30+ Satellites

**PDOP (Positional Dilution of Precision): <1 : excellent, > 4 bad.**
**Motivation (a) 30+ constellation, (b) combine systems**

## International Committee on GNSS

**The ICG was set up by the United Nations Office for Outer Space Affairs (UNOOSA)**
**ICG is „***A forum to discuss Global Navigation Satellite Systems (GNSS) to benefit people around the world***“**
**As opposed to the IGS the emphasis is not on scientific, but on outreach issues where system providers and users are working together.**
**The ****Third Meeting of the International Committee on Global Navigation Satellite Systems (ICG)**** is ****organized by the Jet Propulsion Laboratory**** (Ruth Neilan)****, Pasadena, USA, 8 - 12 December 2008****.**

## Report on PNT 2007-2008 Activities

**From the IAG perspective the draft report on the 2007-08 activities is already in excellent shape (in particular the Executive Summary).**
**It is a concise summary of the Board‘s 2007-08 activities and provides in itself the best argument to continue the Board‘s activities.**
**The IAG is very pleased that the case of**
**Commitment to a 30+ constellation**
**SLR reflectors on GPS satellites**
**get appropriate attention and that **
**International collaboration is viewed as an important issue.**