Characterization of an atom interferometer gravimeter with classical sensors for the use in geodesy and geophysics
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(2) Motivation Absolut Gravimetry is dominated by laser interferometers with falling corner cubes In recent years a number of Atom Interferometer (AI) gravimeters have been developed AOSense & µQuans: commercial quantum gravimeter LNE Syrte: Cold Atom Gravimeter IQ LUH: in development (QUANTUS modification). HU Berlin: Gravimetric Atom Interferometer (GAIN) Characterization by comparison with SCG and AG. AGU Fall Meeting San Francisco | 14–18 December 2015. 2.
(3) Agenda. Motivation Atom interferometry Geodetic Observatory Wettzell 2013: GAIN + GWR SCG Onsala Space Observatory 2015: GAIN + GWR SCG + FG5X Summary and Conclusion. AGU Fall Meeting San Francisco | 14–18 December 2015. 3.
(4) Atom interferometry. simplified observation eq. 1 [1 − cos(∆Φ)] 2 ∆Φ = kef f gT 2. P|F =2i =. AGU Fall Meeting San Francisco | 14–18 December 2015. 4.
(5) Atom interferometry g-experimental sequence 1. Magneto-Optical-Trap → preparation of atoms. 2. State selection. 3. Light – atom interaction. 4. Detection of state populations. 5. Tip/tilt mirror → vertical alignment and Coriolis. 6. Vibration isolation. cycle rate of g-measurement: 1.5 s AGU Fall Meeting San Francisco | 14–18 December 2015. 5.
(6) Geodetic Observatory Wettzell 2013: GAIN + GWR SCG November 2013 Two weeks of measurements In parallel to SG-30 Determination of scale factor with 4 × 10−4 uncertainty Calibration with FG5: 1 × 10−3 [Francis and van Dam., (2002), van Camp et al., (2015)]. Difference to gref : 62 ± 64 nm s−2 Error budget dominated by magnetic effect Hysteresis of vibration isolation revealed AGU Fall Meeting San Francisco | 14–18 December 2015. 6.
(7) Onsala Space Observatory 2015: GAIN + GWR SCG + FG5X Four week campaign in February OSG-054 and GAIN: precision → almost 4 weeks of recordings FG5X-220 and GAIN: absolute accuracy → switch of positions after 4 days Improvements of GAIN after Wettzell Magnetic shielding of MOT → quicker setup of instrument → removal of systematic effect Readjustment of vibration isolation Post-correction for residual vertical mirror movement [Le Gouët et al., (2008)] AGU Fall Meeting San Francisco | 14–18 December 2015. 7.
(8) Onsala Space Observatory 2015: GAIN + GWR SCG + FG5X Electronics Rack FG5X-220. Laser System. Physics Package AGU Fall Meeting San Francisco | 14–18 December 2015. 8.
(9) Onsala Space Observatory 2015: GAIN + GWR SCG + FG5X. residuals [nm s−2 ]. 10 5 0 −5 −10 19.2.. 20.2.. 21.2.. 22.2.. 23.2.. 24.2.. Difference of GAIN and OSG-054 from 30 minute averages. AGU Fall Meeting San Francisco | 14–18 December 2015. 9.
(10) OSO 2015 vs. Wettzell 2013. residuals [nm s−2 ]. 20 Onsala Wettzell. 10 0 −10 −20. 0.5. 1. 1.5. 2. 2.5. 3. 3.5. 4. 4.5. 5. days Difference GAIN – SCG (RMS: 3 nm s−2 /6 nm s−2 ). AGU Fall Meeting San Francisco | 14–18 December 2015. 10. 5.5.
(11) OSO 2015 vs. Wettzell 2013 Onsala Wettzell. Allan deviation [g]. 10−8. 10−9. 10−10 100. 101. 102. 103. 104. averaging time [s] Allan deviation of GAIN – SCG. AGU Fall Meeting San Francisco | 14–18 December 2015. 10.
(12) OSO 2015: FG5X-220 100. gravity [nm s−2 ]. 50. 0. −50 set combined. −100. 5.2.. 6.2.. 7.2. 8.2.. 10.2.. 11.2.. 12.2.. Pillar AC (σ = 5 nm s−2 ) and AA (σ = 9 nm s−2 ) with the ḡ of each pillar subtracted. AGU Fall Meeting San Francisco | 14–18 December 2015. 11.
(13) OSO 2015: FG5X-220 and GAIN. AG RMS [nm s−2 ]. 500 FG5X-220 GAIN. 400 300 200 100 0. 0. 20. 40. 60. 80 −2. Seismometer RMS [nm s. 100. 120. ]. RMS of Seismometer vs. AG (FG5X-220 from 4.2.-12.2. and GAIN from 7.2.-12.2.). AGU Fall Meeting San Francisco | 14–18 December 2015. 12.
(14) Summary and Conclusion Results GAIN Continuous operation with minor down time Improvement of sensitivity to < 1 × 10−10 g Difference to FG5X-220 mean g-result 32 ± 39 nm s−2 Error budget dominated by wavefront aberration [Schkolnik et al. (2015)] Confirmation of SCG scale factor with uncertainty 2.6 × 10−4. AGU Fall Meeting San Francisco | 14–18 December 2015. 13.
(15) Summary and Conclusion Results FG5X-220 Measurements under unfavorable conditions due to microseismic activity Results fit to land-uplift determined with previous FG5 Measurements [Timmen et al. (2015)] Currently no indication for orientation dependent instrumental effect → improvement over FG5-220 [Gitlein, (2009)]. AGU Fall Meeting San Francisco | 14–18 December 2015. 13.
(16) Summary and Conclusion Next Steps Comparison with SCG essential for characterization of AI sensitivity and identification of instrumental effects Reduction of systematic effect Participation in international comparison of absolute gravimeters. AGU Fall Meeting San Francisco | 14–18 December 2015. 14.
(17) Thank you for your attention. This work was in part supported by the German Research Foundation (MU 1141/16-1).
(18) Literature I I. Van Camp, M., Meurers, B., de Viron, O., Forbriger, T.: Optimized strategy for the calibration of superconducting gravimeters at the one per mille level. Journal of Geodesy, DOI 10.1007/s00190-015-0856-7, pp. 1–9, (2015). I. Francis, O., van Dam, T.: Evaluation of the precision of using absolute gravimeters to calibrate superconducting gravimeters. Metrologia 39(5), pp. 485–488, (2002). I. Gitlein, Olga: Absolutgravimetrische Bestimmung der Fennoskandischen Landhebung mit dem FG5-220. Wissenschaftliche Arbeiten der Fachrichtung Geodäsie und Geoinformatik Nr. 281, (2009). I. Le Gouët, J., Mehlstäubler, T.E., Kim, J., Merlet, S., Clairon, A., Landragin, A., Pereira Dos Santos, F.: Limits to the sensitivity of a low noise compact atomic gravimeter. Applied Physics B 92(2), pp. 133–144 (2008). I. Niebauer, T. M., Sasagawa, G. S., Faller, J. E., Hilt, R., Klopping, F.: A new generation of absolute gravimeters Metrologia 32(3),pp. 159–180, (1995). I. Schkolnik, V., Leykauf, B., Hauth, M., Freier, C., Peters, A..: The effect of wavefront aberrations in atom interferometry. Applied Physics B 120(2), pp.311–316, (2015). I. Timmen, L., Engfeldt, A., Scherneck, H.-G.: Observed secular gravity trend at Onsala station with the FG5 gravimeter from Hannover. Journal of Geodetic Science 5(1),pp. 18–25, (2015). AGU Fall Meeting San Francisco | 14–18 December 2015. 16.
(19) Annex: ambiguity solution. Fringes with different T from scanning α: ∆Φ = (kef f g − α) · T 2 + ∆φL AGU Fall Meeting San Francisco | 14–18 December 2015. 17.
(20) Annex: Microseismic activity recorded by OSG-054. Time derivation of 1 Hz SCG data. AGU Fall Meeting San Francisco | 14–18 December 2015. 18.
(21) Annex: Error budget GAIN systematic error Budget for the 2nd campaign. Values for the 1st campaign are denoted with an asterisk. The bias was subtracted from gravity measurements.. Systematic effect Raman Wavefronts Coriolis Effect Magnetic Field Effects RF Groupdelay Self Gravitation Ref-Laser Frequency Sync. Vibrations AC Stark Shift (1PLS) Rb Background Vapor AC Stark Shift (2PLS) Vertical Alignment Total. AGU Fall Meeting San Francisco | 14–18 December 2015. Bias [nm s−2 ] −28 0 0 0 19 −12|−10∗ 0|92∗ 0 5 0 0 | 1∗ −16|77∗. Error [nm s−2 ] ±22 ±15 ±10 ±10 ±5 ±5 ±5|50∗ ±5 ±3 ±2 ±1 ±32|61∗. 19.
(22) Annex: Absolute gravity comparisons. First Campaign GAIN gravity value meas. height correction Reference value Difference GAIN–Ref. Second campaign GAIN gravity value meas. height correction Reference value Difference GAIN–Ref.. Gravity nm s−2 9 808 369 285 400 9 808 369 623 62. Uncertainty nm s−2 ±61 ±10 ±18 ±64. 9 817 158 312 727 9 817 159 023 32. ±32 ±10 ±20 ±39. Comparison of absolute gravity values. The vertical gravity gradient was determined previous to GAIN measurements. AGU Fall Meeting San Francisco | 14–18 December 2015. 20.
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