A Fitting Method of Inverting Ozone Concentration Profile Using Ultraviolet Differential Charge-Coupled Device Imaging Lidar

Round 1

Reviewer 1 Report

Ozone is one of the main pollutants in the atmosphere, and detecting its concentration spatiotemporal distribution can provide scientific basis for the prevention and control of ozone pollution. The ultraviolet differential CCD imaging lidar is a new technology for detecting ozone concentration, which can effectively avoid the geometric overlap factor of traditional differential absorption Lidar in the near range. Due to the difference between the ultraviolet differential CCD imaging lidar equation and traditional lidar equation, the original inversion method of ozone concentration is no longer suitable. Based on the characteristics of ultraviolet CCD imaging lidar detection data, the authors in the paper  innovatively proposes a fitting method for inverting the vertical profile of ozone concentration from the ultraviolet CCD imaging lidar equation. It can be found that the proposed method is feasible and reliable by the simulation results.

 This manuscript can be published with considering to the following suggestions.

 1. The expression “ultraviolet band” in the text is suggested to be replaced by“ultraviolet spectrum”.

 2. Please confirm that the font and size of the horizontal and vertical coordinates of all images in the text are consistent.

 3. The wavelengths in equations 5 and 6 are expressed by λ₁ and λ₂, while the ones in other parts of the text are represented by λ_on and λ_off. Please ensure that they are consistent.

 4. In Part 3.1, the ozone concentration and relative error inversed by fitting method under the assumption of heavily polluted aerosol are described, and it is suggested to supplement the corresponding figure.

English wiritng should be improved. There are some chinglish expressiones in the paper, and they are very difficult to understand. 

Author Response

Dear Reviewer,

Thank you very much for your hard work and good suggestions. Our modifications to your comments are as following.

 

Comments and Suggestions for Authors：

 

Ozone is one of the main pollutants in the atmosphere, and detecting its concentration spatiotemporal distribution can provide scientific basis for the prevention and control of ozone pollution. The ultraviolet differential CCD imaging lidar is a new technology for detecting ozone concentration, which can effectively avoid the geometric overlap factor of traditional differential absorption Lidar in the near range. Due to the difference between the ultraviolet differential CCD imaging lidar equation and traditional lidar equation, the original inversion method of ozone concentration is no longer suitable. Based on the characteristics of ultraviolet CCD imaging lidar detection data, the authors in the paper  innovatively proposes a fitting method for inverting the vertical profile of ozone concentration from the ultraviolet CCD imaging lidar equation. It can be found that the proposed method is feasible and reliable by the simulation results. This manuscript can be published with considering to the following suggestions.

 

1. The expression “ultraviolet band” in the text is suggested to be replaced by “ultraviolet spectrum”.

There are two parts in the manuscript that have been replaced.

2. Please confirm that the font and size of the horizontal and vertical coordinates of all images in the text are consistent.

Figures 1, 2, and 7 in the manuscript have been modified for an unified format.

3. The wavelengths in equations 5 and 6 are expressed by λ₁and λ₂, while the ones in other parts of the text are represented by λ_on and λ_off. Please ensure that they are consistent.

The relationship between the backscattering coefficient and extinction coefficient of any two wavelengths described in formulas 5 and 6，which is not limited to λ_on and λ_off. So formulas 5 and 6 have not been modified in the manuscript.

4. In Part 3.1, the ozone concentration and relative error inversed by fitting method under the assumption of heavily polluted aerosol are described, and it is suggested to supplement the corresponding figure.

Figure 6 has been added to invert the ozone concentration and relative error under the assumption of heavily polluted aerosols.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments for author File: Comments.pdf

Minor editing of English language required.

Author Response

Dear Reviewer,

Thank you very much for your hard work and good suggestions. Our modifications to your comments are as following.

 

Comments and Suggestions for Authors：

This paper discussed a fitting method of inversion ozone concentration profile by ultraviolet differential CCD imaging lidar. Some results at different aerosol extinction coefficients, different ozone concentrations and different aerosol wavelength indexes were simulated. The value of retrieved ozone concentration profile with a relative error of about 4% is obtained at ground. The results presented in the paper are interesting but they have no performance improvements compared to traditional device. In my opinion, the innovation and contribution of this paper are limited for this work to be published in Photonics. My main comments are discussed below.

The CCD imaging lidar, in which the camera is spatially separated to observe the laser beam at a certain distance, is a different configuration compared with the traditional lidar, and it is a developing technique by ultraviolet differential CCD imaging lidar to measure ozone concentration profile.

1. Their research group has firstly proposed a method to detect ozone concentration profile based on ultraviolet differential CCD imaging lidar in reference [21]. What is the difference compared with this paper?

Reference [21] is based on the CCD imaging lidar equation to simulate and optimize the hardware system parameters, which is the preparation work before establishing the hardware system. The paper studies the inversion method of ozone concentration based on CCD imaging lidar detection data. Therefore, main content of the two papers is different. Due to the addition of six references, the original reference [21] has been changed to a reference [27].

2. Why did the echo signals have no range square dependence of the ultraviolet CCD imaging lidar equation? What is the relationship with range?

The hardware configuration of CCD imaging system and the backscattering lidar system are different; the sidescattering lidar equation is also different from the backscattering lidar equation. In order to better illustrate the difference, the instrument introduction has been added in Section 2. From the instrument diagram and the sidescattering lidar equation, it can be seen that there is no square relationship between the echo signal and distance. The derivation process is shown in reference [14].

3. The main difference between the fitting method proposed in this paper and the traditional method is whether to make full use of the lidar detection data. The fitting method proposed in this paper improves the data utilization rate. It is not clearly interpreted in the paper. Will it need more computational time?

The paper further explains how fitting inversion methods improve data utilization compared to traditional inversion methods in section 3.2. Although this method make full use of the lidar detection data, the computation time is very short and can be completed in milliseconds.

4. △z is an important parameter, how to choose or decide this parameter to make sure that the ozone concentration is uniform? So are w and v.

On the one hand, the smaller the Δz is, the higher the spatial resolution is, and the easier it is to meet the uniformity of ozone, on the other hand, the smaller the Δz is, the larger the random error is. Therefore, the value of Δz should take into account these two factors, which is usually taken as several tens of meters. The values of w and v are selected by experience.

5. Five simulation signal profiles obtained at five different values of k are analyzed. Why did k always take as 1? The lines when k=1 in Fig.3 (a), (c) and (e) are not visible. Signal profiles are not different when concentration is high?

Simulation signals should reflect the actual situation as much as possible, 5 values of k are taken to represent the diversity of simulation signals. When inverting simulation signals (including measured signals), k is unknown, k needs to be assigned a value. Therefore, it is assumed that k is a fixed empirical value of 1 to invert the ozone concentration profile. From the error of the retrieved ozone concentration, it can be seen that taking 1 for k is reasonable.

Figure 1 is added in the paper, the original Figure 3 has become Figure 4. Due to the small differences in the simulated five ozone concentration profiles when k takes different values, the five profiles in Figures 4 (a), 4(c), and 4(e) overlap and are difficult to distinguish. The echo signal is related to the scattering and extinction of ozone molecules, atmospheric molecules and aerosols. When the ozone concentration is high, the proportion of aerosols in the echo signal decreases, and k is the wavelength index of aerosols. Therefore, when ozone concentration is high, different values of k have little impact on simulating the ozone concentration profile.

6. The atmospheric visibility is greater than 30km. Why are the retrieval accuracy of the ozone concentration profiles computed within the altitude of 3km? What is the relationship between atmospheric visibility and the altitude?

According to the Rayleigh scattering theory, the extinction coefficient of atmospheric molecules is inversely proportional to the fourth power of wavelength, while the extinction coefficient of aerosols is negatively correlated with wavelength, as shown in formula 6 in the text. Therefore, molecules and aerosols have strong extinction and rapid signal attenuation in the UV band. Even if atmospheric visibility is greater than 30 km, the laser detection distance is relatively close in ultraviolet spectral region. Our UV differential CCD imaging lidar instrument has a maximum detection distance of 3 km. Atmospheric visibility is related to the detection altitude of ultraviolet differential CCD imaging lidar. Qualitatively, the higher the visibility is, the higher the detection altitude is. But the quantitative relationship is relatively complex.

7. The value of retrieved ozone concentration profile with a relative error of about 4% is obtained at ground. I think it could not get a conclusion that the retrieved ozone concentration profile is fitted.

Indeed, one test is not enough. Subsequently, numerous comparative experiments have been conducted, with errors within 5%. Corresponding modifications were made in section 4.2.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors propose a fitting method of inversion ozone concentration profile by ultraviolet differential CCD imaging lidar. The results of the simulation and case demonstrate the relationship between many atmospheric parameters and ozone concentration. The content of this paper is attractive. However, there are some contents that need to be added and explained.

(1)    Introduction: the background is not sufficiently provided in the introduction and should be elaborated. The relevant research content with the ultraviolet differential CCD imaging lidar should be supplemented. Please add some of the research done by other researchers.

(2)    Case: please supplement the composition of the ultraviolet differential CCD imaging lidar system used. Besides, the description and interpretation of the experimental results are inadequate.

 

It is recommended that the author revise and polish the article.

Author Response

Dear Reviewer,

Thank you very much for your hard work and good suggestions. Our modifications to your comments are as following.

 

Comments and Suggestions for Authors：

The authors propose a fitting method of inversion ozone concentration profile by ultraviolet differential CCD imaging lidar. The results of the simulation and case demonstrate the relationship between many atmospheric parameters and ozone concentration. The content of this paper is attractive. However, there are some contents that need to be added and explained.

1. Introduction: the background is not sufficiently provided in the introduction and should be elaborated. The relevant research content with the ultraviolet differential CCD imaging lidar should be supplemented. Please add some of the research done by other researchers.

The introduction has added some of the research done by other researchers, such as CCD imaging system for hyperspectral total ozone unit designed by Liang Shaolin, and A new retrieval method for Ozone concentration at the troposphere based on differential absorption lidar proposed by Fan Guangqiang, etc. There is no relevant reference on ultraviolet differential CCD imaging lidar to detect ozone concentration except the papers published by our research group.

2.  Case: please supplement the composition of the ultraviolet differential CCD imaging lidar system used. Besides, the description and interpretation of the experimental results are inadequate.

The introduction to the ultraviolet differential CCD imaging lidar system has been added in section 2. The experimental results were further described and explained in section 4.2.

 

Author Response File: Author Response.pdf