ACCURATE GEOID HEIGHT DIFFERENCES COMPUTATION FROM GNSS DATA AND MODERN ASTROGEODETIC OBSERVATIONS. Dr. Evangelia Lambrou ASSIST.

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1 NATIONAL TECHNICAL UNIVERSITY OF ATHENS SCHOOL OF RURAL AND SURVEYING ENGINEERING DEPARTMENT OF TOPOGRAPHY LABORATORY OF GENERAL GEODESY ACCURATE GEOID HEIGHT DIFFERENCES COMPUTATION FROM GNSS DATA AND MODERN ASTROGEODETIC OBSERVATIONS Dr. Evangelia Lambrou ASSIST. PROFESSOR NTUA International Symposium on Gravity, Geoid and Height Systems GGHS October 01 Venice, Italy

2 Imperative need became the unification of the height datum over countries. The unification requires difficult height transference The well-known formulas h or Äh Probably it s time for the revival of the astrogeodetic leveling which accurately determines the slope of the geoid surface relative to the ellipsoid surface in long distances. That is the independent calculation of the components ξ and η Three alternative modern ways to perform astrogeodetic observations by the use of high-end instrumentation and software are proposed for precise determination of the components ξ and η of the order of ±0".01 thereinafter so are the geoid undulation differences ΔN by a few mm accuracy

3 The basic concept î Ö A A -ö A Vertical Plump line ç A (Ë A - ë A ) cosö A C ε Α ξ D η 90-Φ 90-φ Λ λ B basic meridian Greenwich î î cos ç ç sin S East Geodetic horizon North astronomical meridian geodetic meridian σ ( mm) Ν σξ = 0.1 '' σξ = 0.05 '' σ ΔΝ S ΑΒ 1 (cos Α sin Α) σ ξ S ΑΒ σ ξ 5 = 0.0 '' σξ σξ = 0.01 '' 50 Distance(Km)

4 THE SYSTEM OF NTUA Hardware,special manufactured cable Drawing software in Leica geobasic language Bidirectional communication UTC time registration The system hardware connections TOTAL STATION GPS RECEIVER PPS OUTPUT ANTENNA GPS RS 3 1 V METEO DATA LOGGER BATTER Y

5 THE SYSTEM OF NTUA The unique system and method For accurate determination 0.01 of astronomical coordinates Φ,Λ the same stars are used latitude (Sterneck method), the transit zenith angle longitude (Mayer method) transit times GPS4000DL pps output Time precision sec Time registration by the total station of 1msec Angular accuracy ± 0.5 = ±1.5 cc the precision and the stability of the instrument clock the personal equation of the observer. there is an average delay of 0.3sec

6 THE EXTERNAL ACCURACY date Φ Star pairs Λ stars 9/1/ /5/ /6/ /6/ /11/ /05/ Mean Value standard error of a single measurement σ Φi = σ Λi =

7 THE EXTERNAL ACCURACY Φ Λ difference (arcsec ) The fluctuation of the Φ and Λ between the sets is of the order of st nd 3rd 4th 5th 6th Sets considering that σ Φ =σ Λ =0.01 σ ΔΦ σ Φ σ ΔΦ z 95% Δ σ ΔΦ z 95%

8 THE GENERATION OF IMAGING TOTAL STATIONS high resolution cameras( External and internal) Digital targeting Automatic digital Zoom Captures and registers image for every measured point Wi-Fi card,bluetooth Wireless connections to the internet Windows CE on board Digital joystick Remote handling via PC and internet connection

9 e- Survey A total remote handling of a total station and its measurements.

10 By using imaging total stations wireless internet connection by using a smart phone clock synchronization with UTC time every second by 0.001sec. the resolution of the incorporated camera, 1.3Mpixel POLARIS Star of magnitude 4 Star of magnitude 5 date Φ Star pairs Λ stars 4/04/

11 σ ση('') η By using the Laplace equation á ç tanö ç tanö cot φσ ΔΑ ΔΑ sin φ latitude(o) σ φ Astronomical azimuth A About 100 observations to Polaris star σ A =± 0.1 time information by an accuracy of the order of 4-5sec date Φ Star pairs η 15/06/ ±

12 CONCLUSIONS An independent, of the local height datum, procedure for the geoid differences determination. Due to the revival of the astrogeodetic observations by means of high-end instrumentation and software. The determination of the ξ and η components is realized by 0.01 An accurate determination of the variation of the geoid of the order of -3 mm can be achieved About one hour is adequate for the measurements The use of the NTUA s system ensures external accuracy of the order of 0.01 for the Φ and Λ The 0.001sec is essential for the time registration.

13 The Laplace equation via the astronomical azimuth it is free of the accurate UTC time registration requires visibility between the points Ν determination of the order of cm. The IMAGINE total stations: Give the opportunity of remote observations via a PC s screen Meet the standards of the required time registration. Ensure accuracy of the order of 0.05 for the Φ and Λ determination namely 1cm for the Ν definition. The resolution of the incorporated camera will be improved The independently calculated Ν can be used for the: Definition or unification of the height datum between countries Height connections between remote points Overseas height transference between islands or countries for the unification of the national height datum. Creation of a precise geoid map of large areas or countries. Enriching of the data of the global geoid models

14 NATIONAL TECHNICAL UNIVERSITY OF ATHENS SCHOOL OF RURAL AND SURVEYING ENGINEERING DEPARTMENT OF TOPOGRAPHY LABORATORY OF GENERAL GEODESY ACCURATE GEOID HEIGHT DIFFERENCES COMPUTATION FROM GNSS DATA AND MODERN ASTROGEODETIC OBSERVATIONS Dr. Evangelia Lambrou ASSIST. PROFESSOR NTUA website: International Symposium on Gravity, Geoid and Height Systems GGHS October 01 Venice, Italy