Review Reports - Calibration of Automatic Sun Photometer with Temperature Correction in Field Environment

Round 1

Reviewer 1 Report

Review Comments

[Manuscript Title]
Calibration of automatic sun photometer with temperature correction in field environment

[Summary]
The authors proposed a calibration method for sun photometer with temperature correction. After the temperature correction, which calibration coefficients were obtained for the bands that the influence of temperature are negligible, relative error and absolute error much reduced, namely, the quality of AOD estimation much improved.

[Broad Comments]
The presentation is clear, I think, and I have only minor comments listed below.

[Specific Comments]

Line 29: …sun photometer CE318 [1]. Especially in …
Rewrite as “…sun photometer CE318 [1], especially in …”.

Line 81: 3.2 Voltage data screening
It is section 3.1.

Line 82: CE318-T593 is installed …, it is affected …
Some conjunctive word (because, since, and so on) is needed at the beginning of the sentence.

Line 86: expressed by DN
Please write the formal name of DN.

Line 100-101: Equation (1)
Is it exp(-m×τλ)?

Line 184: RE of the actual AOD
The word “actual” is confusing. Is that true value? Or, estimated value? I guess the latter because there are two “actual” values before and after the calibration.

Figure 6
I think the word “percentage” (max = 100) of the vertical axis is a little confusing. It might be better to use “fraction” or “ratio” (max = 1).

Author Response

Dear Reviewer,

Thank you very much for your time involved in reviewing the manuscript entitled “Calibration of automatic sun photometer with temperature correction in field environment” (Manuscript ID: remotesensing-1493055) and your very encouraging broad comments：“The presentation is clear, I think, and I have only minor comments listed below.” on it.

We appreciate your clear and detailed feedback. We discuss each of your comments individually along with our corresponding responses in the reminder of this letter and hope that the explanation has fully addressed all of your concerns. To facilitate this discussion, we first retype your comments and then present our responses in red.

Point 1: Line 29: …sun photometer CE318 [1]. Especially in … Rewrite as “…sun photometer CE318 [1], especially in …”.

Response 1: Thanks for your valuable advice. And we modified ‘E’ to ‘e’ and added ‘,’ before ‘e’ in the line 30. And due to another reviewer’s suggestion for this paragraph, we changed the previous sentence on Line 29 to the current sentence: “The measurement accuracy of field spectroradiometers such as the sun photometer CE318 is easily affected by the ambient temperature [1, 2], especially in a typical continental climate area like Dunhuang with a relatively large temperature difference between day and night.” in the line 29-32.

Point 2: Line 81: 3.2 Voltage data screening. It is section 3.1.

Response 2: Thanks for your careful checks. We corrected it in the line 89.

Point 3: Line 82: CE318-T593 is installed …, it is affected …

Some conjunctive word (because, since, and so on) is needed at the beginning of the sentence.

Response 3：Thanks for your valuable advice. We added “Since” at the beginning of this sentence, as shown in line 90.

Point 4: Line 86: expressed by DN

Please write the formal name of DN.

Response 4：This is really a good suggestion. We added “digital number” before “DN”, as shown in line 94-95.

Point 5: Line 100-101: Equation (1)

Is it exp(-m×τλ)?

Response 5：Yes, it is . Thank you very much for your careful inspection. We modified the Equation (1) in the line 108-109.

Point 6: Line 184: RE of the actual AOD

The word “actual” is confusing. Is that true value? Or, estimated value? I guess the latter because there are two “actual” values before and after the calibration.

Response 6：Thanks for your advice. We modified “the actual AOD” to “the estimated AOD” in the full manuscript.

Point 7: Figure 6

I think the word “percentage” (max = 100) of the vertical axis is a little confusing. It might be better to use “fraction” or “ratio” (max = 1).

Response 7：Thanks for your great advice. We modified “percentage” to “ratio” in Figure 6. Also, we modified “percentage” to “ratio” in the other positions of this paper, which is the line 21 and line 238 respectively.

We would like to take this opportunity to thank you for all your time involved and this great opportunity for us to improve the manuscript. We hope you will find this revised version satisfactory.

Sincerely,

Shuyu Chen

Address: School of Optoelectronics, Beijing Institute of Technology, Beijing

E-mail: 3120190517@bit.edu.cn

Author Response File: Author Response.pdf

Reviewer 2 Report

This is a general review.

line 39 - Write out the element names when appearing for the first time.
It's not a bad idea to label the main components of the sun photometer in Fig 1
line 82 - remove "too"
Figures in the results section - perhaps add minor ticks for easy readability
Figure 6 - label each panel along with the caption description you have

Author Response

Dear Reviewer,

Point 1: line 39 - Write out the element names when appearing for the first time.

Response 1: Thanks for your careful checks. Due to another reviewer’s advice, the element (Si, InGaAs) appeared in the line 16 for the first time. We added their names (Si: silicon, InGaAs: indium gallium arsenide) in the line 16.

Point 2: It's not a bad idea to label the main components of the sun photometer in Fig 1.

Response 2: Thanks for your valuable advice. After consulting the information of CE318, we added a sentence: “It mainly consists of a sensor head and a collimator, a protection case with solar panel and a robot that controls two mutually perpendicular rotation axes” and a reference “[10]” after this sentence in the line 72-74. The most important, we marked the main components of CE318 with different color boxes and notes on Figure 1.

Point 3: line 82 - remove "too".

Response 3：Thanks for your suggestions on the details of the article. And we removed “too” in the line 90.

Point 4: Figures in the results section - perhaps add minor ticks for easy readability.

Response 4：Thanks for your valuable suggestions on the figures in this paper. We added minor ticks on Figure 2 to Figure 4 in the results section. Also, we added minor ticks on Figure 5 and Figure 6 in the validation section for easy readability.

Point 5: Figure 6 - label each panel along with the caption description you have

Response 5：Thanks for your valuable advice about Figure 6. The corresponding caption description was added in the upper right corner of every panel. And every panel was labeled at the bottom.

We would like to take this opportunity to thank you for all your time involved and this great opportunity for us to improve the manuscript. We hope you will find this revised version satisfactory.

Sincerely,

Shuyu Chen

Address: School of Optoelectronics, Beijing Institute of Technology, Beijing

E-mail: 3120190517@bit.edu.cn

Author Response File: Author Response.pdf

Reviewer 3 Report

In the introduction, you mentioned that the ambient temperature affects the calibration coefficients. I would recommend that you mention this in more detail in the manuscript along with the physical background for reader's understanding.
In the methodology part, the wavelength 870 nm and 440 nm were selected under the assumption that these two bands were not affected by temperature. However, there are no validations and/or tests to confirm that this assumption is true.
It would be nice to improve figure 3. It's hard to understand because of the similar colors and many legends.

Author Response

Dear Reviewer,

Point 1: In the introduction, you mentioned that the ambient temperature affects the calibration coefficients. I would recommend that you mention this in more detail in the manuscript along with the physical background for reader's understanding.

Response 1: Thanks for your valuable advice. We mainly made the following changes to this manuscript:

1, In the paper submitted last time, the first paragraph is : “During the measurement in the field environment, ambient temperature has an impact on the calibration coefficients of sun photometer CE318 [1]. Especially in a typical continental climate area like Dunhuang with a relatively large temperature difference between day and night. The maximum working temperature difference of CE318 can exceed 70 °C[2]. Some studies have shown that the CE318 can cause large data deviations when working in environments with large temperature difference [2,3]. Therefore, it is quite important to perform temperature correction on CE318.”. And consulting the relevant papers, we modified this paragraph to : “ The measurement accuracy of field spectroradiometers such as the sun photometer CE318 is easily affected by the ambient temperature [1, 2], especially in a typical continental climate area like Dunhuang with a relatively large temperature difference between day and night. For the sun photometer CE318, the measurement error of Si detector at 1020 nm can reach about 0.3% [3] and InGaAs detector at 1639 nm can reach about 1% [4] respectively when the ambient temperature changes by 1 °C. The maximum working temperature difference of CE318 at the Dunhuang site can exceed 70 °C [5]. This may cause a huge measurement error. If the measurement error due to temperature difference is not considered, the incorrect calibration coefficients and retrieval results will be obtained by the observation data of CE318. Therefore, it is quite important to perform temperature correction on CE318.”

2, In this modified paragraph, we added reference [3] and [4]. In the reference [3], we can know that the measurement error of Si detector at 1020 nm of CE318 can reach about 0.3% from the figure of photosensitivity temperature characteristics of Si detector. In the reference [4], we can know that the measurement error of InGaAs detector can reach about 1% from the figure of photosensitivity temperature characteristics of InGaAs detector.

3, In order to make the manuscript more harmonious, we added the paragraph: “As shown in Figure 2(a), is -0.3031 and is 41.7067 at 1020 nm. is -3.5293 and is 204.2777 at 1639 nm from Figure 2(b). Therefore, the absolute value of temperature correction coefficients at 1639 nm are bigger than those at 1020 nm respectively. In other words, InGaAs detector at 1639 nm of CE318 is more susceptible to temperature than Si detector at 1020 nm of CE318, which is also a verification of the previous theory [3, 4].” in the line 170-175.

Point 2: In the methodology part, the wavelength 870 nm and 440 nm were selected under the assumption that these two bands were not affected by temperature. However, there are no validations and/or tests to confirm that this assumption is true.

Response 2: Thank you very much for your valuable suggestions on this part. As for this part, we mainly made the following changes to this manuscript:

1, After consulting the relevant papers, we added a sentence : “ The gas absorption of 870 nm and 440 nm are less than other bands of CE318 according to Giles [7]. What’s more, Si detector at 300-900 nm is less affected by temperature compared to Si detector at 1020 nm [1-3, 7] and InGaAs detector at 1639 nm [4]. ” in the line 146-149.

2, And we added references [1]-[4] and [7]. From the reference [1]-[3] and [7], we can know that Si detector at 300-900 nm is less affected by temperature compared to Si detector at 1020 nm. From the reference [4], we can know that InGaAs detector at 1639 nm is much affected by temperature. From the reference [7], we can know that the gas absorption of 870 nm and 440 nm are less than other bands of CE318.

Point 3: It would be nice to improve figure 3. It's hard to understand because of the similar colors and many legends.

Response 3：Thank you very much for your precious advice on Figure 3. And we replaced the solid dots of the same shape in Figure 3 with solid dots of different shapes and changed colors of dots. Also, we changed the shape of the solid dots in Figure 4 and Figure 5.

We would like to take this opportunity to thank you for all your time involved and this great opportunity for us to improve the manuscript. We hope you will find this revised version satisfactory.

Sincerely,

Shuyu Chen

Address: School of Optoelectronics, Beijing Institute of Technology, Beijing

E-mail: 3120190517@bit.edu.cn

Author Response File: Author Response.pdf