Aeronautics Application of Direct-Detection Doppler Wind Lidar: An Adapted Design Based on a Fringe-Imaging Michelson Interferometer as Spectral Analyzer^†

Round 1

Reviewer 1 Report

The following is a review of the manuscript by Vrancken and Herbst, with the title: “Aeronautics Application of Direct-Detection Doppler Wind Lidar: An Adapted Design Based on a Fringe-Imaging Michelson Interferometer as Spectral Analyzer.” The manuscript presents an overview of a direct-detection Doppler wind lidar (DD-DWL), including details about the instrument design and the parameters important for the analytical performance determination. Furthermore, the manuscript presents a set of responsibly performed and analyzed, ground-based measurements to validate the performance.

While some of the material presented here was previously published, I find this manuscript to be a very useful overview of the effort and highly valuable to the community in combination with the real-world observations and the candid discussion of the instrument performance. In fact, the frank discussion about what “did not work so well” is not often found in the literature and potentially very helpful for other members of the community.

I find the manuscript well organized and well written with clear and informative illustrations. I only offer a few minor, mostly editorial, comments and suggest that the authors consider them before the manuscript is published.

(1) Line 319: Instead of saying: “Taking exemplarily, and for ease of calculus, …” I suggest: “Taking, for example, and for ease of calculation,…” particularly since the term “calculus” is typically used for the specific branch of mathematics.

(2) Line 349: Instead of saying: “…a more comprehensive simulation should be used that takes also account of physical phenomena,” I suggest “…a more comprehensive simulation should be used that also accounts for additional, real-world physical phenomena.”

(3) Line 498: Instead of saying: “…(even less precise for farther ranges)…,” I suggest: “…(even though less precise for farther ranges)…”  -- I believe that is what the authors want to convey here.

(4) Line 535: should read: “And lastly….”

(5) Line 559+ should read: “The laser transmitter used for these experiments is by no means optimized or adapted to the currently targeted application, however it serves the purpose well.”

(6) Line 603+ should read: “The pulse-to-pulse power variation is taken into account by normalization…”

(7) A question about the discussion around line 720: While I understand that especially the timing of the return signal (range) would be different, would it be helpful to use a tilted spinning disk with a retro-reflecting surface to produce a known (Doppler shifted) return for testing? See e.g. Gault et al., Proceedings of SPIE Vol. 4306 (2001).

(8) Line 814 should say “of this 30m-long…”

(9) Line 869: I suggest rewording this conclusion to: “The random distribution of wind measurements of the FW-FIMI demonstrator achieves values in a range as low as 0.4 to 0.65 m/s, yielding:”

(10) Line 894: I suggest rewording this conclusion to: “No significant slope error, i.e., a dependence of the wind speed uncertainty on the observed wind speed, was found in addition to (and the presence of) the random error.

(11) Line 896 should read: “Finally, we analyze…” or “Lastly, we analyze…”

(12) Line 938: I suggest re-wording to: “Thus, both seem adequate to be used for modeling the performance of such a DWL system.”

(13) Line 940 should read: “This last finding is of particular importance for the validated…”

(14) Line 947 should read: “…has the dual purpose…”

(15) Line 961 should read: “may be regarded as quite…”

(16) Line 978 should read: “… merits to be pursued further.”

(17) Line 981+: I suggest: “Our present setup requires repeated re-calibration (currently by sweeping the laser through the FSR, which may not be available for other laser developments), which, we suspect, is a significant cause for the bias in the measurement.”

(18) Concerning the slow drift shown in the first 5min of Figure 8:  I wonder whether it would be useful to show the temperature of the interferometer and/or the temperature of the optical bench, both of which can presumably change the phase of the fringe for different reasons . Maybe an image fiducial could help with this in the future, depending on where the problem is found to be. This might be a non-issue, given that the transmitted line can be continuously used for calibration and the interferometer/instrument is temperature stabilized, but I thought I’d mention it in case useful.

Finally, I am aware of a similar concept suggested in 2013 by Englert and Siskind (US Patent 8,355,120, could be mentioned in context?), using a Michelson with tilted gratings rather than a tilted mirror (~ grating with only one groove), and it is great to see that this two path interferometer technique is providing a good solution for the given measurement challenge. I congratulate you on this body of work and the nice write-up.

 

 

Author Response

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Reviewer 2 Report

This manuscript demonstrates a direct-detection Doppler wind lidar based on a fringe-imaging Michelson interferometer. The Theoretical explanation is very clear, the application scenarios and necessity of the DD-DWL are clearly explained. The results between DD-DWL and CDWL are credible and well-discussed. This manuscript is a pretty good work and impressed me, I think this work can be published on the Remote Sensing, but the authors still need to make some minor revisions to the manuscript.  The detailed suggestion can be seen in the supplement word.

Comments for author File: Comments.pdf

Author Response

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