Calibration of a superconducting gravimeter with an absolute atom gravimeter

Atom gravimeters based on atom interferometry offer new measurement capabilities, by combining high sensitivities and accuracies at the best level of a few tens of nm.s⁻² with the possibility to perform continuous measurements. Being absolute meters, their scale factor is accurately determined and do not need calibration. Because of their high sensitivity and low drift, superconducting gravimeters are the key instruments for the continuous monitoring of gravity variations. Nevertheless, being relative meters, they need to be calibrated.

We revisit a 2015 one month long common view measurement of an absolute cold atom gravimeter (CAG) and a relative iGrav superconducting gravimeter, which we use to investigate the CAG long term stability and calibrate the iGrav scale factor. The initial measurement has already been presented at EGU 2016. Here finalized, we present how it allowed us to push the CAG long-term stability down to the level of 0.5 nm.s⁻². We investigate the impact of the duration of the measurement on the uncertainty in the determination of the correlation factor and show that it is limited to about 3‰ by the coloured noise of our cold atom gravimeter. A 3-days long measurement session with an additional FG5X absolute gravimeter allows us to directly compare the calibration results obtained with two different absolute meters. Based on our analysis, we expect that with an improvement of its long term stability, the CAG will allow to calibrate the iGrav scale factor to better than the per mille level (1σ level of confidence) after only one-day of concurrent measurements during maximum tidal amplitudes.