Earth Surface and Interior Focus AreaSpace Geodetic Networks for Maintaining the Reference Frame

• Geodesy's Critical Contributions to NASA (Earth Science)– Defines, maintains and improves the Reference Frame

• Staying ahead of NASA’s evolving scientific requirements– Inter-Connects measurements over space (globally) and time (decades)

and technology evolution• All observations/instruments placed within this one framework

– This infrastructure is composed of the:• Physical networks• Technologies that compose them, and• Ongoing scientific analysis and model development that define the

reference frame

• Why NASA?– Needed to support NASA science programs, goals and missions– NASA is one of the foremost space technology agencies in the world

• Geodetic Challenges to Achieve Roadmap Goals

– Erosion of geodetic capabilities in face of declining resources and increasing demands

– Integrating new technologies seamlessly while maintaining the long-term stability of the reference frame

– Achieving 1 mm reference frame stability

• Strategies for Meeting Challenges– Implementation of new technologies– Unified & balanced approach to utilization of available

measurement techniques– Continued evolution of geophysical models and analysis – Leveraging the benefits available to NASA through established

international cooperation– Earthscope and NGS cannot meet national priority objectives

without valuable global NASA assets (domestic agencies?)– Better overall program focus and integration

• Current and Future Requirements– Science Areas

• Definition of the ocean surface, sea level change (altimetry) • Land surface change (with INSAR) • Ice budget• Static and time-varying gravity field (?), mass distribution, tides• Tests of relativity• POD capability of GPS and SLR….

– 1mm over ten years for sea and ice level change studies– SESWG report quote -” ITRF and EOP, hence the networks [VLBI, SLR,

GPS], should continue to be maintained and improved and their data routinely acquired at the best possible accuracy and temporal resolution.”

– Roadmaps: Earth science, oceans - [ John - cite the relevant or implied roadmaps that require geodetic networks]

Second Challenge: Renovation of the Space Geodetic Network

Importance of NASA’s Space Geodesy Program– Provides continuity of observations in space (globally) and time (decades)

• e.g. sea-level, ice volume, land subsidence and erosion, crustal deformation– Provides navigation of satellites, space probes, telescopes

• e.g. Topex-Poseidon, Cassini, DSN, VLBA– Enables NASA science exploration capability in mass transport, ocean

circulation, formation flying, remote sensing, physics• e.g. GRACE, UAVSAR, ICESat, COSMIC, SCIGN and PBO, SRTM, J2, Lens-Thirring

– NASA developed space geodesy and provides the leadership for space geodesy nationally and globally .

• e.g. IGS,IVS,ILRS,IERS– Strong synergies between Earth-Sun, Solar System, and Universe exploration

and communications requirements• e.g. positioning, tracking, and pointing within celestial & terrestrial reference

frames,DSN, limb sounding and geodetic imaging– Critical to national defense and civilian activities

• e.g. radar calibration, trajectory tracking, gravity fields, navigation, surveying, commerce, flight safety, USNO, NRL, NOAA , EarthScope partnerships

Science and Technology Challenges

– Science requires better than 1 mm reference frame accuracy• Sea-level change, glacial mass balance, gravity field

variability, ocean topography and circulation• Present Frame accuracy is 1 cm or worse

– Geodetic systems require replacement before 2010 • Creaking bearings and sagging antennas-

– Yarragadee laser station and Gilmore Creek VLBI antenna celebrating 25th anniversaries

• Moving on:– GPS,Galileo,GLONASS GNSS signals in

transformation• Invasion of XM Radio:

– VLBI S and X band spectrum squeezed by commercial and government users

Strategy for Meeting These Challenges– Develop new network technology:

• VLBI- test small S, X, K broad- band antenna systems • SLR- Continue development of SLR2000 automated systems• GPS- Develop new GNSS capable software receiver• Continue development of real time capability: e-VLBI, GDGPS

– Program Development• National Geodetic Observatory study, INDIGO, and GGOS

developing geodetic roadmap• Develop ESTO and partnership funding while advancing program

with existing program funds• Collaborate with DSN on VLBI and SLR technology development

for tracking and communications• Integrate geodetic operations management• Develop synergies e.g. FAA, DoD, Exploration Directorate • Develop new modeling and analysis algorithms

Very Long BaselineVery Long BaselineInterferometryInterferometry

(VLBI)(VLBI)

Satellite LaserSatellite LaserRangingRanging (SLR)(SLR)

Global PositioningGlobal PositioningSystem System (GPS)(GPS)

30 Station Network International VLBIService (IVS)Strength: Earth Orientation

37 Station Network37 Station NetworkInternational LaserInternational LaserRanging Service (ILRS)Ranging Service (ILRS)Strength:Strength:Center of Mass Center of Mass ScaleScale

>300 Station NetworkInternational GPSService (IGS)Strength:Site velocity

Technologies– SLR

• kHz lasers• Automation and 7/24 operations• More accurate retroreflector targets

– Saved missions: ERS1, GFO1,METEOR3,….• GPS and SLR combined provide very accurate POD

– VLBI• Smaller antennas• e-VLBI• Higher rate recording

– GNSS (GPS, GLONASS, Galileo)• More frequencies better suited for analysis• Densification of ground systems• Upgraded receivers (better S/N, signal structure, etc.)• Expanded LEO tracking

– Integration of techniques• Knowledge base integration• Solution-level integration• Observation-level integration

Linking Requirements to Sources

• Tapley• Ries• GLOSS - 1mm over ten years-

Woodworth• SESWG report pg 31 report

1mm/year surface displacement over 50 km

Earth Surface and Interior Focus AreaReference Frame of Space Geodetic Networks

• Why do we need a reference frame?– Long term, systematic measurements of the Earth system

require the availability of a terrestrial reference frame (TRF) that is stable over decades and independent of the technology used to define it

– The space geodetic networks provide the critical infrastructure necessary to develop and maintain the TRF and the needed terrestrial and space borne technology to support the Earth Science Enterprise goals and missions.

– This infrastructure is composed of the:- Physical networks,- Technologies that compose them, and- Scientific models and model development that define a TRF

• Current and Future Requirements• First among the requirements is the realization and

maintenance of the terrestrial reference system, since this is the background to which all local and global variability is tied. Errors in the frame map directly into errors in observable motions and mass changes. (ref Tapley email)

• 1mm over ten years for Sea level change studies• SESWG report quote -” ITRF and EOP, hence the

networks[ VLBI, SLR, GPS], should continue to be maintained and improved and their data routinely acquired at the best possible accuracy and temporal resolution.”

• GGOS?

•Challenges–Rusty network and stations, declining resources–Losing capabilities–Need to maintain existing reference frame geodetic systems–New capabilities and technologies must be integrated

•New Technologies–SLR improvements in automation and . (SLR 200)–- VLBI smaller antennas, e-VLBI–- GPS - modernization, Galileo, collective GNSS, densification of reference frame