|Starting in 1998, ozone profiles were derived from a DIAL tropospheric ozone lidar at the Université de la Réunion (80m, Reunion Island) and then in 2012, this instrument has been moved up to Maïdo Observatory (2160m, Reunion Island). The manuscript examines the recent DIAL performances after this altitude change and aims to be a reference for the further use of the DIAL tropospheric ozone data acquired at Maïdo Observatory (Reunion Island). Authors describe firstly the DIAL ozone data processing and secondly the lidar instrumental description and performances. Finally, they compare the lidar ozone profiles data set with ECC sondes (launched at the Maïdo Observatory and Gillot site (9m)), with data from a ground based FTIR spectrometer (operating at the Maïdo Observatory) and with the space-borne IASI data. From this comparison based on monthly climatologies over distinct period and over distinct partial columns, they conclude on the agreement.|
Comments on the title:
Despite my recommendation in AMTD to withdraw from the title “Part 1”, which was not meaningful, authors kept “Part 1” in their ATM manuscript submitted. Their justification is : “this paper is the companion article of an upcoming one dealing with stratospheric ozone measurements in Reunion Island, which will be the “Part 2”.”. As far as I know I haven’t seen a reference to this paper in the text nor any introduction whilst they mention futures studies on aerosols p 6 line 11 in the manuscript. Has it been even more submitted as a companion paper? From my point of view, the link seems weak and the justification is not acceptable. Final decision is under the responsibility of the editor and editorial board.
This paper, indeed well in the scope of the journal, does not meet the standard criteria to be published in AMT. I am not addressing here a whole list of suggestions/corrections. The main motivations for rejection are :
1/ Despite my previous recommendations the manuscript still remains with incomplete, undefined, imprecise or incorrect definitions or equations (in particular in section 2.2 and 2.3, and in section 4 equation 7 and 8, see brief details further). An equation in the text should help the reader to understand precisely what calculation has been done which is not the case here. DIAL lidar ozone data retrieval, a quite complex technique to provide accurate results, is extensively documented in previous published papers. Here the synthesis is unclear and explanations appear not under control. Missing Page 3, line 22 the following reference “Harris at al. 1998” (“N. Harris, R.D. Hudson, and C. Phillips, Editors, WMO, SPARC/IOC Ozone Profile Trend Assessment, WMO Global Ozone Research and Monitoring Project - Report #43, Geneva, 1998.”).
2/ Regarding the instrument itself and data processing (sections 2), no instrumental improvement is described in this manuscript, it has been detailed in previous papers. Additionally, no improvement in the technical ozone retrieval from DIAL despite authors planned to consider in the future the impact of aerosols and interfering gases. That would be for sure a valuable improvement to motivate a publication in AMT as you mentioned the impact of a Chilean volcano eruption on your data set. I do not agree with your “saturation” definition p 4 line 10. Saturation from my point of view occurs when the photo counting system cannot handle the high intensities received by the detector. Saturation can’t be low, it is saturated or not. What is “desaturation”, then? In Eq 4, what is k, what is n, where is the altitude dependence? I want to know when your calculations are time or altitude or wavelength dependent (a general comment on your equations). Section 2.3, absolutely unclear (eq 5: associated error whilst you use standard deviation and signal to noise ratio; unclear from lines 10 to 15 including eq 6) should be replaced. When and where occurs the error propagation (line 12 p5)? It is not explained. What is xi, etc? Please be accurate in your description. To conclude, by considering the previous published publications, a change in the altitude location of the instrument is not a sufficient motivation to support a publication in AMT and given the text clarity and improvements, the paper appears as not mature from the technical point of view.
3/ Regarding the LIO3T performances (section 3), they were evaluated considering 427 LIO3TUR profiles against 84 LIO3T profiles. Why the lidar LIO3TUR operates at night to increase SNR (signal to noise ratio, undefined) is not justified. The “overlap factor” is not defined. Comments on Figure 3 should be addressed straightforward on the LIO3T vertical resolution improvement/deterioration as compared to LIO3TUR. Line 15 p 6 is not consistent regarding your Figure 3 and 4. Line 32 p 6 do not specify the instrument except if you refer to figure 4 and you did that also in lines 16 -19 page 6. My feeling is that section 3.2 needs to be reorganize/rewritten to better distinguish LIO3TUR from LIO3T informations. Benefits from this instrument altitude change vs vertical resolution and uncertainties are not brought into light. I found the message in your concluding remarks not enough straightforward and clear (p7 line4-6 – SNR, uncertainty, detection noise with respect to ozone variability in UT/LS).
4/ Regarding the comparison with ancillary data.
A/ ECC sondes : Number of profiles or partial columns included in the comparison is missing in p7, line 8-12. They are only 8 for ECC sondes launched (at night time???) at Maïdo Observatory in collocation and time-coincidence within ± ?? hours (be accurate). They are 37 for ECC at Gilot day time launched compared to full night LIO3T with a ± ?? hours delay (be accurate)… Introduce your data set precisely once in section 4 and do not repeat later. What is N, M, MCD and rn? It should be a very simple calculation and text is unclear. Consider fig 5 in Gaudel et al., 2015 as an example, it is simple and clear. I only agree with your r (which is rn in the text, what n stands for?) if you specify that is altitude dependent (z). But now how to interpret D? You can’t conclude on a bias high or low with D? You just provide a value and conclude it is in good agreement… Further in the text authors specified that some of the 8 compared cases (how many exactly?) are sampled in a context of high aerosols due to volcano Calbuco eruption (Chile, not located). The full date and time page 8 lines 3 and 4 are missing even if table 2 is providing dates but it is impossible to learn which is which. My feeling is that you have here a valuable material to make progress in your retrieval technique. I am not sure the line 9-18 are essential to interpret your results and figures at the moment because you do not take into account the aerosols in the DIAL retrieval and you do not show the data. It is just to introduce further studies??? If not essential, withdraw and also the text repeated in lines 23-28 p 8 or if essential improve the retrieval. In the Figure 5 caption, you use “accuracy” which is undefined. Now if we consider the 37 ECC sondes launched at Gillot, what is the benefit of this second comparison to external data because launched within less time coincidence and collocation, i.e. leading to increase the probability to sample different air masses. You conclude on a greater D (9.4% as compared to 6.8% for Maïdo). The justification for a comparison with a second set of ECC sondes is not provided... What are the benefits to your demonstration? Finally is LIO3T bias high or low as compared to LIO3TUR? You can’t use D to conclude on this last point. Need clarifications.
B: FTIR ground based, IASI and LIO3T : 12 partial columns are taken in the intercomparison for the ground based FTIR and 39 for IASI, both instruments over 3 years. D is 11.8 and 11.3% respectively, that is greater than with ECC sondes by almost a factor of 2. A long text to describe instrument and data retrieval compared to really poor conclusions and interpretations (p10 lines 4-11).
5/ Regarding the data set and climatologies (section 5) : Fig 11 is a valuable result and I suggest to add an ECC climatology over 2013-2015, the LIO3T period considered. That is interesting but the discussion is poor : I haven’t seen much improvement in the quality of LIO3T climatology as compared to ECC sondes and even more in UT/LS. What benefits are you expecting from this instrumental altitude change as compared to routinely ECC sondes measurements… Please compare your results to what Gaudel et al, 2015 have published in figure 4. What can you conclude? Are your results consistent? For all those reasons, I found the paper not mature.
Minor details (among the lot of remaining errors…) :
- A very poor and confusing English style. In addition, relationship between sentences and paragraphs are deficient.
- Along the text, correct use of higher (an altitude is higher) and greater (an amount is greater). “Ancillary data”, is very imprecise as compared to “O3 external data set”.
FINAL CONCLUSIONS AND RECOMMENDATIONS : I don’t accept this manuscript at this stage for a publication in AMT, even in the scope of the journal. I recommend a new submission accordingly to my comments with exact definitions, to increase the number of LIO3T measurements (including 2016 profiles at least) and to improve the retrieval technique by taking into account the aerosols. In order to provide a substantial, consistent and condensed technical overview of the DIAL technique at Maïdo Observatory, I suggest to add part 2 dedicated to stratospheric ozone. Therefore the new submitted paper with substantial material could be valuable for further ozone studies which use the DIAL lidar at Maïdo Observatory as expected by authors and co-authors.