Thank you for your good question and advice. the high-quality GNSS/levelling-based height anomalies are used to check the refined GGMs for obtaining the optimal combination degrees. Thus, the refined GGMs provide better local quasi-geoid results. We have added descriptions and contents in the revised manuscript. The combination of the satellite-only GGM with the EGM2008 in this study is based on a pure complementation of the spherical harmonic coefﬁcients at a speciﬁc degree in this paper, which is different from rigorous combination that is done on the basis of the normal equations and co-variance by a least-squares. The purpose of this pure combination can provide better local quasi-geoid results, it is said that it can obtain the characteristics of spatial "localization" for quasi-geoid. Combining the satellite-only GFM with EGM2008 by applying some sophisticated weighting approach usually combines the maximum degree and order of the satellite-only GFM and the EGM2008. Because the degree errors of the satellite-only GFM increase with the increase in degree and order, the noise starts to dominate the signals at high degree and order. The noise of satellite-only GFM maybe introduce by sophisticated weighting approach. In addition, the rigorous combination based on the sophisticated weighting approach usually needs the full error variance-covariance matrix of the spherical harmonic coefﬁcients, but, the full error variance-covariance matrix of the spherical harmonic coefﬁcients might generally not be available. Although the obtained results are already quite promising, it can be expected that the refined GFMs provide a guidance for determining the quasi-geoid or the geopotential value of the vertical datum in China. However, the combination of the satellite-only GGM with the EGM2008 in this study is based on a pure complementation of the spherical harmonic coefﬁcients at a speciﬁc degree. However, such a procedure might cause a spectral gap between both models. In the next step, the rigorous combination or a smooth transition (such as: using hanning window) will be considered to derived the refined GGMs. Please refer to page 17, Line 544-545.
I have a few minor points (marked in the attached PDF) and two general points, which I like you to address.