This paper, titled ‘Spectral performance analysis of the Fizeau interferometer onboard ESA’s Aeolus wind lidar satellite’, investigates the factors influencing the measurement accuracy of wind speed by the Fizeau interferometer. The Fizeau interferometer serves as a critical component in the wind lidar system. In this study, the instrument function of the line shape is analyzed based on the Fizeau fringes observed from Aeolus. Additionally, the broadening effects due to angle of incidence (AOI), field of view (FOV), laser pulse characteristics, and defects are numerically examined. Furthermore, the impact of line broadening on fringe shift and Doppler wind measurement accuracy, as well as the influence of Rayleigh-Brillouin background signals on signal-to-noise ratio (SNR) and measurement accuracy, are discussed. Finally, the potential performance of upgraded Fizeau systems with optimized parameters is proposed for future applications. This work is highly significant and merits publication. I recommend accepting after minor revisions.

1. In the analysis of contributory factors to the Fizeau fringe profile, the authors identify several key elements that influence the profile, including nonlinear fitting procedures, laser pulse characteristics, field of view (FOV), angle of incidence (AOI), plate defects, fringe skewness, and the impact of Rayleigh-Brillouin scattering. Could the authors provide a detailed analysis of how each factor affects the accuracy of Fizeau fringe characterization, particularly in terms of full width at half maximum (FWHM), and consequently, the precision of the final wind measurement?

2. In this paper, the uniformity of the laser spot is not mentioned, does it affect the final profile of Fizeau fringe?

3. I think the program of the ALADIN has been demonstrated, the author analyzes the instrument function and showed the AOI a fewhundred urad, so could you give an explanation what kind of changes make a so large AOI?

4.The author shows the influence of the defects such as sinusoidal and surface defects on the designed Fizeau, does the spherical defect of the mirror broaden the fringes?

5.On line405, Fig.6 b should be Fig.6 (b); line 555, the Fig.14 a should be Fig.14(a) and the same as shown online 574, please have a check.

6. On line 650 for LSB an explanation should be made.

7.The unit of AOI in line 434 has a writing error.

This is an excellent paper.  I found it a pleasure to read and review.  It describes a detailed analysis of the Fizeau interferometer used to estimate Mie-scattered winds as part of the Aeolus mission.  The paper is well-organized, describing the Aeolus mission and the role of the Fizeau interferometer, the interferometer itself, and then logically proceeding to characterization of the interferometer on the ground and a summary of the performance of the component during the mission.  It concludes with a very credible hypothesis for the observed reduced performance observed on-orbit,  and describes improvements that could be incorporated into the interferometer design for a follow-on mission that could significantly improve performance.

The paper is both informative and tutorial.  I guess I was a bit surprised that a Fizeau interferometer has not previously been analysed using a wave-optics approach, but the utility of the approach for this analysis is certainly justified and appropriate.

In my opinion, this paper could be published without revision.  If the paper is returned to the authors, a couple of descriptions in the text could benefit from a bit more explanation:

Line 546:  The sentence beginning with “The simulation analysis…” notes that the frequency estimation algorithm was modified.  A bit more discussion here on the frequency estimation algorithm would be informative.

Line 640:  Although the values for r and f_ab agree with those of specified in the previous section, it isn’t clear to me how they were determined.  Were these determined through simulations?