Utilization of O<sub>4</sub> slant column density to derive aerosol layer height  from a space-borne UV–visible hyperspectral sensor: sensitivity and case  study

Park, Sang Seo; Kim, Jhoon; Lee, Hanlim; Torres, Omar; Lee, Kwang-Mog; Lee, Sang Deok

doi:https://doi.org/10.5194/acp-16-1987-2016

Articles | Volume 16, issue 4

https://doi.org/10.5194/acp-16-1987-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-16-1987-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 16, issue 4

Research article

|

23 Feb 2016

Research article |

| 23 Feb 2016

Utilization of O₄ slant column density to derive aerosol layer height from a space-borne UV–visible hyperspectral sensor: sensitivity and case study

Sang Seo Park, Jhoon Kim, Hanlim Lee, Omar Torres, Kwang-Mog Lee, and Sang Deok Lee

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Final revised paper (published on 23 Feb 2016)
Preprint (discussion started on 17 Mar 2015)

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

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RC C2476: 'Review of "Utilization of O4 slant column density..." by S.S. Park et al.', Anonymous Referee #1, 12 May 2015
- AC C9376: 'Response to Reviewer 1', Jhoon Kim, 17 Nov 2015
RC C6873: 'Interactive comment on “Utilisation of O4 slant column density to derive aerosol layer height from a spaceborne UV-visible hyperspectral sensor: sensitivity and case study” by S. S. Park et al.', Anonymous Referee #3, 15 Sep 2015
- AC C9391: 'Response to Reviewer 2', Jhoon Kim, 17 Nov 2015

Peer-review completion

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

AR by Jhoon Kim on behalf of the Authors (02 Dec 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (02 Dec 2015) by Michel Van Roozendael

RR by Anonymous Referee #3 (18 Dec 2015)

Suggestions for revision or reasons for rejection

General comments

The authors did substantial modifications on their new version of the manuscript. They took account
most of the comments highlighted during the review process. I appreciate to see more details
explicitly described in the different sections, like the methodology of the error analysis or a higher
number of study cases in the last chapter. Moreover, the section about the sensitivity of the AEH
retrieval to the different O 4 spectral bands is more concise and goes straightforward to the key
message: the importance of the 477 nm band, compared to the other ones. The error analysis
performed here look now more realistic. In particular, as expected, the analysis surface albedo and
AODs (among other parameters) show to have large impact on the AEH retrieval.
The results presented at the end on real OMI observations, focused over ocean, show very large
differences with the CALIPSO dataset. However, the authors make links with the error analysis and
insist on the different parameters to improve (in particular the surface albedo, and the aerosol
properties) prior to the retrievals. In spite of these differences, this work will be useful for the
community who works on this topic.
I still have a few remarks, mostly minor. I would appreciate the authors to address them, before the
final publication, as I believe they will help the readers.

Specific comments

1) Explanations about the LUT in Section 2.2
The authors compare their own retrieved O4 SCDs to the OMI NASA products. For that, it is
mentioned that the WinDOAS software is used, and then a Look-Up Table as described in Table 2.
However, the link between these 2 elements is not completely clear.
I believe that a few lines should be added before the beginning of the 3rd paragraph. I guess that a
number of simulations were performed with VLIDORT for different SZA, VZA values. And then a DOAS
fit was performed to deduce O4 SCD with WinDOAS. And finally, a LUT could be generated. Am I
correct? Please explain it.

2) Surface albedo value of 0.1 in Section 4
I am not sure, but this value may be a little high for OMI observations over ocean. In my view, ocean
surface is in general darker than land surface (although it can be highly variable depending on ocean
conditions, as mentioned by the authors). Depending on seasons, OMI surface albedo values over
land are usually (but not always) below than 0.1 in the visible. Could the authors explain or add 1 or
2 references justifying this value?

3) Sensitivity of AEH accuracy to AOD (Section 3.2.1)
This section is very interesting, and confirms that the feasibility to retrieve the aerosols altitude, from
passive sensors, depends on the aerosol amounts. Later on, in the manuscript, it is also mentioned
that angles (SZA, VZA) have a significant role. I believe that overall the continuum reflectance (which
directly depends on these 3 parameters) drives the AEH accuracy (as the O4 shielding effect, through
the SCD, is constrained by the continuum reflectance magnitude). In case of low continuum
reflectance, aerosols (and even clouds) have limited effects on the slant column It is somewhat
mentioned in [Acarreta et al., 2004]. You could refer to it. Moreover, such a sensitivity was found in
[Sanders et al., 2015] although a different spectral band was used.
This section and your plots look consistent with the findings of [Chimot et al., 2015], where different
approaches were employed for analysing the interplay between the OMI cloud retrievals, through the
O4 spectral band, and the presence of aerosols. Could you please verify and confirm this for
consistency?

4) Review some typos / sentences
I would recommend, to perform a final check of the manuscript and to reformulate some sentences,
where necessary. There are sometimes some incomplete sentences, or some formulations are not
clear.
Below are given some examples, but this list is, I think, not exhaustive:
Page 6, Line 125: “This new algorithm is applied to the radiance data”: I think here the author should
say it was applied to the O2-O2 SCD, available in the OMI NASA product.
Page 6, Line 135: “atmospheric molecules and aerosolS” (final s to be added to “aerosol”)
Page 14, Line 307: “On the other hand, the sensitivity of the O4I at 477 nm has significance to
estimate AEH” => “is a significant variable to estimate AEH”
Page 14, Line 328: “materials” => properties
Page 15, lines 345-346: I do not understand the statement “from OMI ... respectively”. Please
reformulate.
Page 15m Line 348: please justify the AOD uncertainty of 0.1 (reference?).
Page 16, Line 354: “for small AOD at low AEH, which has small shielding effect” => since here
aerosols are at very low altitude (close to the surface) and O4 SCD increases, I think the term
enhancement would be more appropriate than shielding. Indeed, in that case, aerosols have a
similar effect than albedo, as they increase the sensitivity of most of the O4 column. They do not
shield here the O4 column.
Page 16, Line 360: “decreases as the altitude” => do you mean aerosol altitude?
Page 17, Line 377: “scattering aerosolS” (s added)
Page 17, Line 378-379: “It effectively brings albedo effect dominant for aerosol layer”. Please
reformulate this, and use enhancement effect, as opposite to shielding effect.
Page 17, line 382: “which is corresponds to” => which corresponds to?
Page 18, Line 411: “noticeable effects ON THE phase function” (on the added)
Page 18, Line 418: “which setS”
Page 19, Line 434: “aerosol layer shut off” => aerosol layer attenuates
Page 19, Line 438: ”by the albedo effect to the O4I is larger for the absorbing aerosol” => I do not
understand the last part of this sentence. Please reformulate.
Page 19, Line 446: “”AEH increaseS and AOD increaseS”
Page 20, Lines 450-452: “However...the reference case”: Please check English and formulation
Page 20, Line 457: “less” => lower or smaller?
Page 23, Line 521: “a half and a quarter” => 50% and 25%
Page 24, Line 556: What is FMF? I did not find this term earlier in the manuscript. Further, please
define the CALIOP AEH. How did you compute it? Or was it available in the CALIOP product?
Page 25, Line 579: “on the dateS”

Referee Report: PDF

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ED: Reconsider after minor revisions (Editor review) (04 Jan 2016) by Michel Van Roozendael

AR by Jhoon Kim on behalf of the Authors (12 Jan 2016) Author's response Manuscript

ED: Publish as is (20 Jan 2016) by Michel Van Roozendael

AR by Jhoon Kim on behalf of the Authors (28 Jan 2016) Manuscript

Short summary

The sensitivities of oxygen-dimer (O₄) slant column densities (SCDs) to changes in aerosol layer height are investigated using simulated radiances by a linearized pseudo-spherical vector discrete ordinate radiative transfer (VLIDORT) model, and the differential optical absorption spectroscopy (DOAS) technique. A new algorithm is developed and tested to derive the aerosol effective height for cases over East Asia using radiance data from the Ozone Monitoring Instrument (OMI).

Utilization of O4 slant column density to derive aerosol layer height from a space-borne UV–visible hyperspectral sensor: sensitivity and case study

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Utilization of O₄ slant column density to derive aerosol layer height from a space-borne UV–visible hyperspectral sensor: sensitivity and case study