Comparison of noise-levels between superconducting gravimeter and gPhone gravimeter

For comparison of noise levels between superconducting gravimeters（SGs） and gPhone gravimeters, we conducted an experiment in which we carried out co-located observations of gravity changes by the same gPhone gravimeter and Superconducting Gravimeter（SG） at Wuhan, Lhasa and Lijiang stations respectively, and the observation at each station lasted approximately 2 months. We calculated the root mean square（RMS） of the gravity residual in each station and selected the five days in which the gravity residuals had the minimum RMS representing the background noise level as a quiet period. Based on the gravity residuals in these five quiet days, we calculated the mean power spectral density（PSD）, seismic band noise magnitude（SNM） and sub-seismic band noise magnitude（SSNM）. Furthermore, we simulated the influence of scale-factor error on SNM. We found that the SNM of the SGs ranged between 1.22 and 1.50 and the SSNM ranged from 3.96 to 4.74 during the experiment. The SNM of the gPhone gravimeter ranged from 2.93 to 3.06, and the SSNM of the gPhone gravimeter ranged between 4.17 and5.29. The SNM of the SG at Wuhan station was the highest among three SGs, while the corresponding SSNM was the lowest. The SG at Lhasa station, in contrast, had the highest SSNM and lowest SNM. The PSDs of gPhone gravimeters in high-frequency bands, including the seismic bands, were much larger than those of SGs. In the sub-seismic bands, SGs can approach or reach seismograph detection level. In the band frequency below 3×10-5 Hz, SGs and gPhone gravimeter have lower PSDs than seismometers,indicating that high-precision continuous gravimeters are better than seismometers in detecting longperiod signals. The variation of SNM caused by the scale-factor is generally in the range from -0.092 to 0.083, which has little influence on SNM result.