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Gerald Mader National Geodetic Survey (NGS) Silver Spring, MD USA

Experimental Results from “BigAnt”, a Large Format Antenna for High Quality Geodetic Ground Stations. Gerald Mader National Geodetic Survey (NGS) Silver Spring, MD USA. Andria Bilich National Geodetic Survey (NGS) Boulder, CO USA. Dmitry Tatarnikov Topcon Positioning Systems Moscow, Russia.

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Gerald Mader National Geodetic Survey (NGS) Silver Spring, MD USA

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  1. Experimental Results from “BigAnt”, a Large Format Antenna for High Quality Geodetic Ground Stations Gerald Mader National Geodetic Survey (NGS)Silver Spring, MD USA Andria Bilich National Geodetic Survey (NGS)Boulder, CO USA Dmitry TatarnikovTopcon Positioning SystemsMoscow, Russia

  2. Background • All GNSS antennas sacrifice performance to be man-portable • Permanent networks can use antennas optimized for performance without regard to size or weight (within reason) • Thanks to Dmitry Tatarnikov & Topcon we have prototypes to test

  3. BigAnt “Standard” Chokering High-Impedance Ground Plane 3m

  4. BigAnt with Radome

  5. Chokering & BigAnts Chokering BigAnt-2 BigAnt-1 34m 44m

  6. Another View BigAnt-2 Chokering BigAnt-1 44m 34m

  7. Test Setup Receivers: • Septentrio AsteRx2eH (tracks both BigAnt-2 & chokering) • Topcon Net-G3A on BigAnt-1 & BigAnt-2

  8. Test Plan • Antenna Calibration for BigAnt • PPP solutions for Chokering & BigAnt • Compare linear combinations & quality factors

  9. Relative Antenna Calibration Summary 44 m Test Antenna Reference Antenna • Get L1 & L2 Phase Center Offsets (PCO) of test antenna with respect to reference • From single differences solve for clock & Phase Center Variation (PCV) • Use absolute calibration for reference to convert test antenna to absolute Since: geometry removed no troposphere no ionosphere no relative clock Problems: limited sky coverage poor coverage at zenith no azimuth solution multipath Residuals show only remaining effect – PCV

  10. Single Difference Phase Residuals vs. Elevation L1 With the positions known, and the relative clocks removed, and with no propagation effects, the phase residuals clearly show the relative PCV as a function of elevation. These residuals are averaged in 5° bins to produce the PCV that goes into the antenna calibration file. L2

  11. Absolute Antenna Phase Center Variation (PCV) for BigAnt-1 & D/M_T Choke Ring PCV (mm) The absolute calibration of the choke ring antenna is used to convert the relative calibration of BigAnt into an absolute calibration. The PCVs & PCOs for the standard choke ring and BigAnt (standard choke ring + high impedance ground plane) are shown here.

  12. GIPSY PPP – phase residual  > 200kg Concrete tiles resting on surface

  13. GIPSY PPP positions - vertical > 200kg Weather station 13km away Concrete tiles resting on surface

  14. BigAnt Sinking meters Day of year, 2014

  15. GIPSY Phase & Range Residual RMS vs ElevationAll Satellites Range Phase m cm cm cm Chokering Chokering RMS BigAnt-2 BigAnt-2 Elevation Mar 31 2014 Elevation Mar 31 2014

  16. Single Difference Phase RMS vs Elevation All Satellites BA2 - CR L2 L1 BA2 - CR BA2 - CR RMS (mm) RMS (mm) BA2 – BA1 BA2 – BA1 Elevation June 18 2014 Elevation June 18 2014

  17. DD Phase – PRN 13Ion-Free, Fixed-Integer, Various Reference Satellites BigAnt 2 – Choke Ring BigAnt 2 – BigAnt 1 DD Phase (m) Elevation June 18 2014

  18. L1 Range Multipath - PRN 13 RMS = 0.206 m RMS = 0.127 m Choke Ring L1 Range Multipath (m) BigAnt BigAnt Elevation June 18 2014

  19. L2 Range Multipath - PRN 13 RMS = 0.205 m RMS = 0.126 m Choke Ring L2 Range Multipath (m) BigAnt Elevation June 18 2014

  20. WIDE LANE - PRN 13 RMS = 0.173 cy RMS = 0.099 cy BigAnt Wide Lane (cy) Choke Ring Elevation June 18 2014

  21. SIGNAL / NOISE RATIO - PRN 13 BigAnt L1 L1 Choke Ring L2 L2 Time (hr) Mar 31 2014

  22. Kinematic Phase Solution – Up Component BigAnt-2 - Choke Ring & BigAnt-2 – BigAnt-1 RMS = 0.008 RMS = 0.005 RMS = 0.008 RMS = 0.005 Up RMS (m) Time (hr) June 18 2014

  23. Possible Locations for NGS BigAnt Corbin Richmond

  24. Mounting BigAnt 6” diameter outer piers 12” diameter inner pier ̴3’ 3.5’ ̴2-3’ The antenna foundation final pier heights are yet to be determined but should not exceed 3.0 ft. in height above the surrounding ground surface. The antenna will be fastened onto the foundation piers using 5/8-11-in. threaded rod imbedded in the top of each pier. Antenna foundations consists of a single 12-in. diameter center pier (located in the center of a 3.5-ft. radius circle with 8 6-in. diameter support piers evenly spaced along the circumference. All piers are schedule 40 PVC pipe filled with concrete and anchored to subsurface coral.

  25. BigAnt Calibration Reference Antenna Reference Antenna Get L1/L2 phase center positions Get L1/L2 PCOs & PCVs Step 1 Install Chokering on Central Pier. Take sufficient data. Step 2 Assemble High-Impedance Ground Plane around Chokering

  26. Last Words • Improved SNR • L1: < 30° • L2: 10°– 90° • Phase & Range multipath significantly improved • Implications • Down-weighting low elevation data • Tropospheric solutions (vertical) • Interchannel range bias • Ionosphere solutions • Clock solutions • Further testing is planned • Poster Paper – Wednesday 11:00

  27. Thank You ! Time for comments / questions ?

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