General Comments

An excellent, well-written and readable paper on an autonomous, small, versatile, precise and robust lidar instrument. The instrument is an excellent idea, and it uses many different state-of-the-art and even cutting-edge lidar techniques. The manuscript describes the method and a prototype, presents a sample dataset and elaborates well on the kind of questions in atmosphere research that can be studied with an arrray of a reasonable number of such instruments. The text, figures, tables and equations are useful, clear and easy to understand.

Specific Comments

Somewhere, for instance near the end of the Introduction, it would be fair to make reference to the following publication by Kaifler and Kaifler (2020), which describes a similar small, precise, robust and autonomous lidar instrument: https://doi.org/10.5194/amt-2020-418 . A sentence or two about similarities and differences between VAHCOLI and CORAL would be useful.

Line 169-173: It does not become clear why no active control of the outgoing laser beam is necessary. Perhaps one important piece of information was not described, or the formulation is not clear enough.

Consider adding, for instance in section 2.4, information about the chopper rotation frequency and beam diameter at the chopper, which determines the opening time near 5 km in Figure 6.

Line 220 and perhaps several other places in the text: Consider adding "line-of-sight winds".

Line 225: consider adding "to derive metal atom number densities" or similar.

In section 3, Table 1, and Figs. 6-7, consider adding where these measurements were performed. From lines 163-165, the reader can guess that this was Kühlungsborn, but the information might be useful near the figures.

In lines 575, 586, and perhaps other places in the manuscript, please consider that to most non-specialist readers, an "ice layer" is a solid piece of plane ice, as on a frozen puddle. Perhaps another term, such as "layer of ice particles" or similar would be clearer to the non-specialists?

At the end of the Introduction, in line 571, or in the Oulook and Conclusion, consider adding the approximate price per unit and the approximate operation costs. I would, however, understand why these numbers might be difficult or awkward to specify.

Technical Corrections

line 177: "mirror"

lines 199 and 200: is the "max" in R^max and k^max not written as an index on purpose?

line 422: I believe the correct word is "anisotropic"

Lübken and Höffner presenting a novel concept of distributed small lidar instruments named Vertical And Horizontal COverage by LIdars (VAHCOLI) to investigate the atmosphere as a whole. The revolutionary lidar instrument, capabilities, and technical concept are excellently presented. Even some basic knowledge has been recapitulated to guide the reader and make this part of the manuscript well understandable. The relevant science applications are presented in paragraph 5. It mainly focuses on dynamical processes of the atmosphere that are clearly described and discussed in relation to their relevance to VAHCOLI.

Overall, this manuscript is well written, the novelty of the concept, lidar instrument, and relevant science applications are presented clearly and sound. The manuscript has high significance for the community related to lidar instrumentation and atmospheric measurements.

General Comments

The paper presents the development and first implementation of a lidar system that has the  potential to transform observations of the middle atmosphere. The development of these compact and robust wind solid-state wind-temperature capable lidars is a significant technical achievement in itself. Combining precision resonance lidar techniques with Rayleigh and Mie techniques to yield winds and temperature in the troposphere, stratosphere, mesosphere, and lower thermosphere. The fact that these instruments are field deployable as compact  units (1 m) allows deployments of distributed arrays of profilers that will support a variety of new investigations of the middle atmosphere. The paper provides a technical description of the instrument as well as a discussion of investigations that will supported (e.g. waves versus large scale turbulence).

Specific Technical Comments

Overall the paper is well-written, informative, and accessible. However, there are places where more information would be useful, particularly if this paper is to serve as  foundation reference for the VAHCOLI class of lidars.

1) The paper would benefit if some of the technical details were explained in greater detail, particularly in terms of the determination of the frequency stability of the seed laser and the confocal etalon using the Doppler-free spectroscopy (Figure 5). Does the locking use the Pound-Drever-Hall technique combined with the Doppler-free spectroscopy? What are the fundamental limitation of the tuning accuracy and precision based on the Doppler-free spectroscopy. How was the stability of the confocal resonator determined relative to that of the seed laser?

2) The diagram of the lidar system could be presented in more detail as the schematic of record.

3) There are places where the the writing could be polished and made more concise.

Minor point.

The authors note that the lasers were trucked from Aachen to Kuhlüngsborn (~600 km) without significant misalignment. Can they determine the relative contribution of the laser design, the driving skills of the shippers, and the quality of the autobahn conditions to this result?