Lidar Profiling of Aerosol Vertical Distribution in the Urbanized French Alpine Valley of Annecy and Impact of a Saharan Dust Transport Event
Round 1
Reviewer 1 Report
The authors have presented results of study, characterization, and mapping of the content and vertical distribution of local and external aerosols over the French Alpine valley of Lake Annecy, performed mainly by ground-based meteorological Raman lidar and Rayleigh-Mie lidar on board an ultralight aircraft, in the period 13-21 June 2019, as part of the Lacustrine-Water Isotope Inventory experiment 13 (L-WAIVE). Lidar measurements and profiling of aerosol optical properties are complemented by in-situ measurements of aerosol physical and microphysical parameters, supported also by modeling and satellite data on the aerosol/air transport.
General comments
The work falls well within the scope of the journal Remote Sensing.
The manuscript’s title is correct, but reflects only the lidar aspects of the work, although data from a number of other (in situ, satellite and modeling) instruments and sources were also used, whose complementary and/or synergistic interaction with lidar ones appear to be essential from the text.
The abstract adequately presents the content, main results and achievements of the work.
The introduction, to a large extent reasonably, is focused primarily on reviewing and analysing previous research related to field campaigns in Alpine valleys. As can be seen from the cited literature, the authors of the manuscript have substantial experience and contributions from previous such campaigns and research. I attribute to this the considerable number of cited works with their co-authorship (about 1/3 of the literature cited in the manuscript). Although this is a relatively large percentage, I find it quite justified, since most of them are for reference to instruments and methods used in the present work, which are already described in detail in their cited previous articles. And while this is somewhat at the expense of the self-contained character of the manuscript, it helps to avoid unnecessarily overloading its volume with descriptions that are available in detail from previous works. Nevertheless, I think that the authors could (optionally) consider possibilities for some acceptable to them reduce of the number of self-citations, or otherwise to expand the cited literature a bit more with relevant articles by other authors, for example in cases of aerosol studies in a wider context over orographically complex terrains or using other methodologies and instruments. The above recommendation is just wishful thinking and I leave it to the authors to decide whether to accept it or not.
The main objective of the work is appropriately formulated at the end of the introduction, deduced logically from the presented analysis of the cited literature.
The content of the text is well structured, in a methodically correct logical sequence of the presented studies and analyses. The instruments and methods used are well described or referenced.
The language of the presentation, being professionally correct, is at the same time clear and understandable to the reader.
A sufficient amount of numerical and graphical experimental and modeling data illustrating the obtained results, in terms of optical, microphysical and dynamic aerosol parameters, is presented. For all of them, estimates of their uncertainties are given, numerically or graphically, testifying to scientific correctness.
I consider as a merit of the work the approach of the authors to critically analyze the results obtained with the variety of tools used, in their mutual connections and conditionality, which allows them to reveal and show effects of mutual confirmation and/or synergy.
I find that the conclusions drawn are well based on the data and results presented in the paper.
Technical remarks
· Fig (s). 3a, 5a, 6a and 7a present color-coded 3D relief maps of the Lake Annecy valley. They greatly favor the better visualization and understanding of the presented information about flight trajectories, local air circulations, as well as aerosol and meteorological parameters. Overall, their graphical layout and presentation is very good. However, on all of them, the height color bar is labeled “DEM (km)”. First, I think the abbreviation DEM (Digital Elevation Model) is not that widely popular and requires an introduction in the text or in the figure captions. Second, "DEM" by its meaning cannot have a dimension, in particular “km”. I would recommend for the title of the color bars "Elevation (km)" or similar, whereas the model used can be specified separately, what practice exists in the literature.
· In the Abstract (on line 15), in the list of aerosol parameters subject to vertical profiling in the work, along with AEC, LR and PDR, the aerosol optical thickness (AOT) is also mistakenly included, which is an integral/columnar parameter and not a subject to profiling.
· Lines 108,112: “Raman elastic channel(s)”. These probably are technical terminological errors. It is clear from the context that the authors meant Raman channel(s).
· Fig. 1a lacks the x-axis title and the tick-mark labels, which, in addition to being inconsistent with panels b) and c) of the same figure, creates difficulty for the reader in tracking the time to which a corresponding comment from the text refers. It is also the only one of the three that is open on the top side.
· In all three panels of the Fig. 1, the colored parts adjacent to the x- and y-axes obscure the tick marks on those axes.
In summary, I think that the proposed manuscript presents an advanced, systematic, and thorough multi-instrumental study of atmospheric aerosols in the valley of the Alpine Lake Annecy during the considered period, conducted at a high scientific and technological level and presented in an adequate, methodologically correct manner, and in good technical quality.
My overall assessment of this work is highly positive. I believe it will be of significant interest to the journal's audience and the atmospheric research community as a whole. Based on that, I strongly recommend publication of the presented manuscript in Remote Sensing, after minor corrections in the aspect of the remarks stated above.
Author Response
See the attached file
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments on ‘Lidar profiling of aerosol vertical distribution in the urbanized French Alpine valley of Annecy and impact of a Saharan dust transport event’ by Patrick Chazette and Julien Totems. (Article ID: remotesensing-2202795)
General comments:
This paper focuses on the observation of the vertical distribution of aerosol optical properties over the Annecy valley with the combination of a ground-based Raman lidar and an airborne Rayleigh-Mie lidar carried on an ultralight during a period from 12 to 22 June 2019. Also, meteorological parameters as well as space-borne observational data are used to study the transport of aerosol plumes. The combination of ground-based lidar and airborne lidar is beneficial to the understanding of the vertical distribution and transport of aerosols here. Overall, this paper is well-written and many interesting results are reported. Therefore, I recommend the acceptance of this manuscript for publication after addressing the following comments.
Major comments:
l Since only 11-day observation is reported, it is hard to conclude that the results here are representative of the aerosol condition in this region. For example, is there a distinct seasonal variation here? Maybe it is better to give a literature review paragraph to specially state the background and significance of the case study in this manuscript.
l Moreover, less vertical distribution information is shown in the abstract which is unacceptable, especially considering that it is an advantage for lidar.
l In figures 3 and 8 as well as the corresponding text, I strongly suggest the use of PDR instead of VDR, since PDR more reflects the aerosol property and is not related to the aerosol loading.
l In section 5.1.4, the authors state ‘we have assumed a constant LR value as a function of altitude’. Which inversion method (Raman method or Fernald method) do you use to calculate the aerosol extinction coefficient? It is better to state clearly. In section 2, it is suggested to provide more information on the lidar systems (see the specific comments below). Also, it would be better to provide a table that include the relative error for each aerosol optical parameters (i.e., aerosol extinction coefficient, PDR, lidar ratio…).
Specific comments:
l L17, it is better to give the aerosol extinction coefficient values
l L55, [14-18][14,15]?
l L77, June 13 is not consistent with June 12 in the abstract
l L105-106, give the pulse energy of the laser since the temperature and RH(WVMR) are also observed.
l L110, ‘particle depolarization ratio (PDR)’ should be ‘particle linear depolarization ratio (PDR)’
l L113-115, give the wavelength used for two N2 rotational Raman channels
l L124, it is suggested to provide the relative error for aerosol extinction instead of AOT. How do you process the lowermost blind region of the lidar field-of-view in AOT calculation?
l L260, the large values of lidar ratio 115sr on June 18-19 are attributed to the low aerosol loading. However, similar small AOTs are also observed on June 13 (the first day during this period).
l L250, remove ‘(a)’
l L276, ‘3.1.1’ before the subtitle is repeated.
l L288-289 and Figure 1c, in the color bar for PDR, the maximum value should be extended to 30%.
l Figures 3 and 8 as well as section 5.1.2, use PDR instead of VDR.
l L316, ‘low troposphere’, give the altitudes
l L335 & 341, the observational times used in the text should be consistent with those in figure 5.
l L385, ‘foehn effect’ should be consistent with the spelling in figure 7.
l L454-458, give a sentence to explain why ‘transition between mesoscale and synoptic air mass’ can be linked to the variation of PDR at altitudes of 3.0-3.5 km. Also, it is noticed that these altitudes are corresponding to the peak of the aerosol extinction coefficient.
Author Response
See attached file
Author Response File: Author Response.docx
Reviewer 3 Report
This manuscript analysis a Saharan dust transport event using airborne and ground-based Lidar, and shows the vertical distribution of the aerosol. The lidar can provide temperature. humidity and other important atmospheric parameters. The instruments used in the experiment are well descripted, the experimental data is reliable and sufficient, and the discussion improve the understanding of aerosol vertical distribution in mountainous regions and devere convective weather in Alpine valley. This manuscript can be published on the Remote Sensing, but the authors still need to make some minor revisions to the manuscript. Here are some comments:
1. In the Abstract, authors can highlight the use of airborne lidar and vertical ground-based lidar in the Alps for joint observation, and the continuous observation of dust storms and severe convective weather processes might be another highlight.
2. The name of the experiment in Line 68 needs to be reconfirmed, which is different from that in Reference 23.
3. In the Introduction, the significance of the research and the background knowledge are introduced in detail.
4. In the materials and methods, the parameters of the equipment are introduced in detail, and the principle of the equipment and the calibration period of data validity are described. But I think the whole instruments and their calibration can be list together.
5. On the day from 14th to 16th, the clouds may be too thick, so there is no data from the sunphotometer. Why does the aerosol data from the lidar lost a lot, but the temperature and humidity data lost less? Is the cloud less than 500 meters high?
6. If the detection altitude is not high in bad weather, the lidar with large blind area will with larger error in AOT, so the accuracy of lidar data in such weather needs to be explained (16th to 17th).
7. Line250, should be figure2, no figure2a.
8. In Figure 8a, will the airborne lidar or ground-based lidar exceed the effective detection range more than 3.5km?
9. In the paragraph of Line450-458, the threshold values of different types of aerosol pollution are 20% and 30%. The reason should be explained. Are there any references?
10. Line487 needs to reconfirm whether the contents in the brackets are correct.
11. In section 532, using the hypersplit model, why choose the height of 4-6 km? Most of the valid data in this manuscript are below 4.5km. The manuscript should show the results of 3-5 km?
12. The height of boundary layer is an important parameter of pollution transmission, diffusion, and strong convection weather processes. This manuscript should include the analysis and discussion of the height of boundary layer, and further analyze the characteristics of aerosol vertical distribution and the process from dust storm to heavy rainfall.
Author Response
See attached file
Author Response File: Author Response.docx
