Peer review of: The root of anomalously specular reflections from solid surfaces on Saturn’s moon Titan (2020)

(RR2)
Reviewers' comments:
Reviewer #1 (Remarks to the Author):
The authors satisfactorily reworked the manuscript. It is well writen und will cetrainly be of high interest to the scientific community. I gladly recommend this work for publication.
Reviewer #2 (Remarks to the Author):
The authors have made a nice effort in order to clarify their manuscript. I have only a few minor things:
Fig 1A-1E: the width of the echo should be indicated by a thicker line, in a well visible color (not black please).
L. 81-82: is Fig. 1E an example of an anomalous specular radar reflection (ASRR)? In addition, the two 'group' of ASRR in Fig. 1F could be graphically particularized using colors, labels, ...
l. 104-105: 'The maximum-NRCS depends on only the central Doppler bin and thus has a greater weighting from the terrain at the subradar location.' : perhaps a ref. (if it is possible under NatCom format) ?
Fig. 4: please indicate the location of B. and D on map A.
l. 396: Data availability, please mentioned also the tool 'Titan Trek' https://trek.nasa.gov/titan/
Q.: by curiosity : how the NRCS of ASRR compares with NRCS in central part of evaporite deposits proposed by Barnes et al. (2009,2011)?

Reviewer #3 (Remarks to the Author):
The Root of Specular Reflections from Solid Surfaces on Saturn’s Moon Titan
Themanuscriptdefinitelyflowsbetterthanbefore(andhasimproved).Ithinkitcouldbeimproved even more, especially the order of some sections (this will help with the flow).
Abstract:
L20-21: since hydrology means water, you shouldn’t refer to Titan’s methane cycle as “methane hydrologic cycle.” Instead, you could say “Titan’s tropospheric methane cycle” and then talk about how it is akin to Earth’s tropospheric water cycle.” Since the role of CH4 at altitudes above Titan's tropopause are very different than Earth’s water, you should restrict your water cycle and methane cycles comparisons to the two tropospheres.
L39: You mention that Cassini observations (RADAR and VIMS I presume) did not observe liquid reservoirs at the same regions that are anomalously specular to AO/GBT. I’m curious to know if your detections overlap spatially with where Cassini VIMS/ISS observed low latitude tropospheric methane rain/clouds. And also with ground-based AO Keck and Gemini CH4 cloud observations (like those from Schaller et al.)?
Introduction:
L34-41: after southern tropical region, add the range in latitudes – equator to 30S? You could also say “low southern latitudes.” Regardless, just be clear on the meridional (and zonal) locations. This is important b/c I’m immediately thinking about the season and the atmospheric dynamics, and if methane precipitation would be expected for the latitude and time of your ground-based observations.
After Introduction, I would expect a section on “Observations.” Diving right into Results is rather odd since the reader doesn’t know much about the observations, the spatial resolution, footprint size on Titan's disk, how this compares with Cassini RADAR and VIMS (if at all) starting July 2004 (Cassini orbit insertion), etc. In time, you overlap between 2004 and 2008 so this is the place to discuss this.

This would also be a good place to discuss an overlaps with the Keck/Gemini AO observations -- these are the ones that routinely monitored CH4 tropospheric cloud activity from Earth.
Results
Thefirstparagraphisaboutthequalityofdata,thefactthatTitan’sdiskisspatiallyunresolved,what echo spectra look like, etc. This is info on the observations. It is not results. Same goes for most of the panels in Fig. 1.
L 78: It took me a while to actually find the horizontal black lines. Consider increasing their values so the lines stand out better. Or, you could just say (in words) that between xx and xx Hz represents the width of the echo and outside of this range is just noise (if that is what you mean). Again, put all of this type of discussion in “Observations” since you are simply discussing the quality of the data.
L191-192: You didn’t consider ground-based Keck and/or Gemini observations using adaptive optics that did show tropospheric clouds in the tropics during this time period. You need to detail these and address if there are any correlations (e.g., Schaller et al., 2009).
L210:213: What are you trying to say here? That temporal changes are an unnecessary hypothesis? This could be interpreted as somewhat aggressive. Instead, just state that temporal changes are unlikely to explain the AO/GBT ASRR.
L304: remove “.., they are the source of the ASRR.” In the beginning of the sentence you state this so you don’t need to say it again.
L371: Why is there a Methods section following Discussion? I would delete “Methods” and then move the content to the “Observations” section that should follow the Introduction section. The manuscript would then end with Acknowledgements/Author Contributions.
I really encourage the authors to create an Observation section following Introduction. Then, everything about your ground-based observations, combined with Cassini RADAR/VIMS, and Keck/Gemini observations would be revealed early on. I think this’ll make the Results section more concise and moreimpactful.