SPACE GEODESY NETWORK & ITRF Z Minchul LEE 1

Precision Geodesy 2 Source:

The Geodetic Reference Frame (e.g. ITRF)  Requirement (Source GGOS 2020)  Better than 1mm reference frame accuracy  Better than 1mm/yr stability  Accessibility: 24 hours/day (worldwide)  Sea level measurement is primary driver  Space segment: LAGEOS/GNSS/DORIS Satellites  Ground segment: Global distributed network of modern & co-located stations  Improvement over current ITRF performance  How to provide the reference frame  Better global network of Co-located stations (VLBI/GNSS/SLR/DORIS) ~30 globally distributed & well positioned & co-located stations are required  Dense GNSS network distributes the reference frame globally Source: 3

Co-location Site 4 Site where two or more space geodesy close instruments (hundred meters) are operating Surveyed in three dimensions, using classical or GPS geodesy Differential coordinates (DX, DY, DZ) are available

Contribution of Geodetic Techniques to ITRF 5  Mix of techniques is fundamental to realize a frame that is stable in origin, scale, and with sufficient coverage. Source: IAG

Ground Based Space Geodesy Network Source: IAG  Deficiency in current space geodesy network  Insufficient co-location sites  Coverage gap (especially in SLR & VLBI)  Mix of modern system & old system (Need Relocation)  Performance differences in between stations and system (Problem in overall network performance) 6

Example Fundamental Station (NASA Goddard Space Flight Centre, USA)  GGAO has four techniques on site  Legacy SLR/VLBI/GPS/DORIS  NGSLR semi – “operational”  VLBI 2010 system in testing Here will be the prototype location for next generation multi-technique station! 7 Source: IAG

Site Requirements  Site Condition (GGOS Standard)  Global consideration  Geology  Weather & Sky condition  Radio Frequency & Optical Interference  Horizon conditions  Local ground geodetic networks  Electric power  Air Traffic & Aircraft protection  Site Security  Wide-Band Communications  Conceptual 30 Station Network  Australia & New Zealand: 3 Stations  North America: 3 Stations  South America: 3 Stations  Europe: 3 Stations  Africa: 3 Stations  Central Asia: 3 Stations  India/Indian Ocean regions: 3 stations  Far East/Asia: 3 stations  North Pacific - 3 stations  South Pacific - 3 stations 8 Reference accuracy and stability will require 30 globally distributed, multi-technique co-location ground stations!

Technique Activities Making Progress 9  Satellite Laser Ranging (SLR)  Several system operation (KHZ regime)  Increased data yield & daylight ranging on GNSS SVs  Steady progress on new SLR prototype  VLBI  Prototype VLBI 2010 (New 12M antenna)  Other systems in Tasmania/Katherine/Yarragadee stations  GNSS  Multiple Constellation  Additional Frequencies  DORIS  Nearly completed network  Additional satellites  New Beacons  Calibration  GRASP Concept Source: IAG

Future efforts & Progress 10  The First Phase (For 2 years)  Complete the prototype SLR (NGSLR) & VLBI (2010) instruments  Co-locate these instruments with new generation GNSS & DORIS ground stations  Implement modern survey system to measure inter technique vector for co-location  Develop generalized station layout  Start Site evaluation for network station deployment  Complete network simulation based on LAGEOS & GNSS tracking with SLR  Follow Up Phase  Deployment up to 10 stations  Achievement 30 co-location ground stations

References 11  Courtesy of Bernard Minster, National-Requirements/12954http://dels.nas.edu/Report/Precise-Geodetic-Infrastructure- National-Requirements/12954  Michael Pearlman (2010), The Need for Space Geodesy Networks (2010)  Michael Pearlman et al.(2011), Space Geodesy Networks to Improve the ITRF  IAG, On Geodesy and the Global Geodetic Observing System,

The End Thanks for your attention. 12