Performance Evaluation of the Absolute Quantum Gravimeter AQG-B09 Observations for Post-Relocation Calibration of the Superconducting Gravimeter iGrav043

This paper evaluates the performance of the Absolute Quantum Gravimeter AQG-B09 during a four-month co-location (4 Dec. 2024 to 8 Apr. 2025) with the superconducting gravimeter iGrav043 at Todenfeld Observatory, after the relocation of iGrav043 from Luxembourg to Germany. The experiment assessed AQG-B09 under continuous observatory operation and tested whether its gravity record can provide an absolute reference for post-relocation scale factor determination. AQG-B09 and iGrav043 operated on adjacent pillars, while a Scintrex CG-6 measured the local vertical gravity gradient and provided an independent relative-gravity consistency check. The iGrav043 scale factor was estimated from the 4-31 December 2024 co-location interval, before a pronounced non-stationary instrumental drift in January 2025 associated with a hardware-related loss of thermal control. An ordinary least-squares adjustment between AQG-B09 gravity and iGrav043 voltage, including polynomial drift terms, yielded -924.37±0.69 nm·s^-2·V^-1, with relative precision 0.075%. This agrees with the 2022 Walferdange calibration of -924.80±0.75 nm·s^-2 ·V^-1; the values are not significantly different within uncertainties, indicating no detectable relocation-related scale factor change. Residual stability and sensitivity were evaluated using Allan deviation and power spectral density analyses. Hourly AQG-B09 residuals, after applying the classical geophysical corrections (solid Earth tide, ocean tide loading, polar motion, and atmospheric pressure effect), agree with the low-noise iGrav043 reference at the few tens of nm·s^-2 level. Compared with an independent FG5-101 measurement, AQG-B09 shows an absolute-level difference of about 67.6 nm·s^-2, consistent with the Hannover 2024 comparison and not affecting the scale factor, which depends on temporal gravity variations. Although AQG-B09 does not yet reach FG5-type absolute accuracy, it provides a practical, stable continuous absolute reference for observatory gravimetry and post-relocation SG scale factor calibration, provided systematic corrections are controlled and non-stationary SG intervals are excluded.