Experimental assessment of a micro-pulse lidar system in comparison with reference lidar measurements for   aerosol optical properties retrieval

Córdoba-Jabonero, Carmen; Ansmann, Albert; Jiménez, Cristofer; Baars, Holger; López-Cayuela, María-Ángeles; Engelmann, Ronny

doi:https://doi.org/10.5194/amt-14-5225-2021

Articles | Volume 14, issue 7

https://doi.org/10.5194/amt-14-5225-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/amt-14-5225-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 14, issue 7

Research article

|

30 Jul 2021

Research article |

| 30 Jul 2021

Experimental assessment of a micro-pulse lidar system in comparison with reference lidar measurements for aerosol optical properties retrieval

Carmen Córdoba-Jabonero, Albert Ansmann, Cristofer Jiménez, Holger Baars, María-Ángeles López-Cayuela, and Ronny Engelmann

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Final revised paper (published on 30 Jul 2021)
Preprint (discussion started on 31 Oct 2020)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review', Anonymous Referee #1, 26 Nov 2020
- AC1: 'Reply on RC1', Carmen Cordoba-Jabonero, 02 Apr 2021
RC2: 'Review of amt-2020-427', Anonymous Referee #2, 22 Jan 2021
- AC2: 'Reply on RC2', Carmen Cordoba-Jabonero, 02 Apr 2021
- AC3: 'Reply on RC2 (part 2)', Carmen Cordoba-Jabonero, 02 Apr 2021

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Carmen Cordoba-Jabonero on behalf of the Authors (13 Apr 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (13 Apr 2021) by Daniel Perez-Ramirez

RR by Anonymous Referee #1 (17 Apr 2021)

RR by Anonymous Referee #3 (19 Apr 2021)

Suggestions for revision or reasons for rejection

This paper describes a comparison between data collected using the authors Micro Pulse Lidar (MPL) and another lidar from PollyNet. Although the MPL used in this study normally operates as part of the MPLNET, it was removed from its normal station and the data collected during this campaign were processed by the authors with their own processing, calibrations, and data collection techniques. The data collected here are not from MPLNET, nor did they utilize that projects established methodology (including existing calibration process for both polarization and overlap). Therefore the results of this study are not widely applicable, and definitely do not accurately represent the data produced by the MPLNET project. This limits the overall usefulness of this study.
The authors also present a main conclusion of this paper as an accurate overlap calibration is needed to retrieve aerosol properties from an MPL. This is by no means a new conclusion, this has been known since the MPL was first used in the 1990s. It is also why the MPLNET project has long ago established methods to deal with this issue. The methods used by MPLNET were ignored in this study and not well referenced. The authors do cite Berkoff 2003 which describes the basis of the current MPLNET method to retrieve overlap, however they do not discuss the relevance to their process shown in the paper (which is very similar, involving retrieval of the overlap from the two lidar profiles).
In addition, there are a number of errors present in this work and the authors do not present a clear understanding of the polarized MPL. Instead, a very vague and generalized description of the polarization problems is given to describe the causes of bias, for instance the authors say "This offset represents a correction to account for any slight mismatch in the transmitter and detector polarization planes and any impurity of the laser polarization state", and reference older work from non-MPL polarized lidars (that utilize an entirely different optical design) and an older polarized MPL using a different crystal polarizer. This statement is simply vague and inaccurate. The authors just apply an offset to make the polarized MPL data agree better with the Polly lidar, but appear to have no idea what is causing the bias (or how it might manifest in other ways). If the authors attempt to describe their work as an "experimental assessment of a Micro Pulse Lidar system" then they should have an expert level understanding of the instrument itself. None is presented in this paper. Again, the MPLNET project has established methods for calibrating polarized lidars that were not well referenced in this paper. The authors cite a Welton 2018 paper, but do not discuss the findings from it that bear directly on the polarization calibration of MPL instruments.
I do not understand why MPLNET is discussed in this paper, nor mentioned in the acknowledgements. Other than the fact that this lidar normally operates in the MPLNET in Spain, this particular study is from a redeployment of the MPL outside of MPLNET using the authors own processing and calibrations. It should be made very clear in this manuscript that the methods described here are not part of MPLNET, nor applicable to MPLNET as they have previously defined methodologies. If the intention is otherwise, then how that would be achieved is not discussed at all. There appear to be no NASA funded contributions to this work, so why is that included in the acknowledgements section? If this did occur it is not obvious in the paper, if not then this should be removed from the acknowledgements.

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ED: Reconsider after major revisions (04 May 2021) by Daniel Perez-Ramirez

AR by Carmen Cordoba-Jabonero on behalf of the Authors (02 Jun 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (03 Jun 2021) by Daniel Perez-Ramirez

RR by Anonymous Referee #3 (17 Jun 2021)

ED: Publish as is (18 Jun 2021) by Daniel Perez-Ramirez

AR by Carmen Cordoba-Jabonero on behalf of the Authors (18 Jun 2021) Author's response Manuscript

Short summary

An experimental assessment of a polarized micro-pulse lidar (P-MPL) in comparison to reference lidars is presented regarding the retrieval of aerosol optical properties. The evaluation is focused on both the optimally determined overlap function and volume linear depolarization ratio. A P-MPL overlap must be regularly estimated to derive suitable aerosol products (backscatter, extinction, and particle depolarization ratio). This methodology can be easily applied to other P-MPL systems.