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Physical Scintillation Simulation

Physical Scintillation Simulation. Diffraction Grating-Based GPS Physical Scintillation Simulation Results. Kirtland AFB, NM 19 June2012. Dr. Todd Pedersen Capt. Melanie Huffman Mr. R . Todd Parris AFRL, Space Vehicles Directorate, Kirtland AFB, NM.

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Physical Scintillation Simulation

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  1. Physical Scintillation Simulation Diffraction Grating-Based GPS Physical Scintillation Simulation Results Kirtland AFB, NM 19 June2012 Dr. Todd Pedersen Capt. Melanie Huffman Mr. R. Todd Parris AFRL, Space Vehicles Directorate, Kirtland AFB, NM

  2. Attempt to simulate ionospheric scintillation and nav outages by physically altering live GPS signal 2-D L-band diffraction gratings created out of metallic wire “field fence” with holes 12” wide by 4”-12” high (graduated spacing, wide at top, narrow at bottom) One curved panel approx 6’ long One cylinder approx 3’ diameter x 4.5’ high Waved over antenna on rooftop 2 Ashtech Z-12 receivers connected to same antenna via splitter Test of receiver-specific effects or power level discrepancies Experiment Setup Courtesy of C. Mitchell

  3. Implementation • 5 variations: panel only, cylinder only, cylinder topped with panel, cylinder+panel+foam board with metallic tape, 4 metallic tape foam boards in box configuration Cylinder only Topped with panel Foam board added

  4. Receivers • 2 Ashtech Z-12 receivers • S/N 04299 Firmware 1L00-1D04 • S/N 03789 Firmware 1L00-1D04 • Data collection by GPS-SCINDA Version 1.77 on both • Splitter with DC bias to pre-amp powered by RX # 03789

  5. Test Timeline 19:31 UT Antenna connected 19:36 UT “Scintillation” commencement (single flat grating) 19:40 UT Cylindrical grating 19:44 UT Cylinder plus grating on top 19:50 UT Break 19:54 UT Foam board added under top grating 19:57 UT Added foam “wings” 20:01 UT Back to baseline 20:06 UT Foam blockers only 20:10 UT Foam blockers in “box” formation ~24” above 20:15 UT Attempt to produce maximum impact (rapid movement) 20:20 UT End of “scintillation” 20:25 UT Pack up

  6. Positioning ErrorsFirst Half of Test • Identical receivers on same antenna • One has no outages, the other >6 min at a time Some Errors and Extensive Outages Some Errors but No Outages

  7. Positioning ErrorsSecond Half of Test • More severe portion of test (diffraction+blocking) • Some similarity in error patterns, but total outage length differs by > 10x

  8. Fluctuations on Individual Links 03789 • More similarity in gaps on individual links • Absolute signal levels in close agreement 04299 Baseline Mesh Panel Mesh Cylinder Panel over Cylinder Added Foam Baseline

  9. Comparison of L1 and L2 Amplitudes RX 04299 • L2 drops out more frequently • Dispersion effects?-- more amplitude loss at L2? • Grating is more reflective at L2 than at L1 L1 Loss of codeless tracking? L2

  10. Highest Elevation Satellite—L1 • Mean signal level appears to be unchanged from background with wire mesh only RX 03789 RX 04299

  11. Highest Elevation Satellite—L2 • Clear difference in signal levels from cylinder and overhead panel • Much less than amplitude drops from foam board RX 03789 RX 04299

  12. Summary • Transmission grating-based scintillation simulation successful • Clear difference between L1 and L2 effects, significant loss-of-lock and navigation outages • Only minor reduction in amplitude compared to foil tape • Greater distance from antenna may provide even better performance (far field instead of near field) • Positioning outages extremely receiver-dependent • Identical receivers, identical firmware, same antenna, 10X difference in outage length • Should use as many receivers as practical with simulator to get a feel for unit-specific characteristics and statistical range for each receiver type • Test with single unit may be very misleading/atypical

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