A Study of a Miniature TDLAS System Onboard Two Unmanned Aircraft to Independently Quantify Methane Emissions from Oil and Gas Production Assets and Other Industrial Emitters

Round 1

Reviewer 1 Report

The article describes two independent deployment methods (fixed-wing and multi-rotor) for quantifying methane emissions utilizing the in situ TDLAS sensor. And the
controlled release experiments are introduced in the article. The paper is interesting for the community, I have a few comments as below

Point 1: What is the speed of the fixed-wing and multi-rotor in the controlled release experiments, how long does it take to complete one test, the authors may need to provide more details.

Point 2: As the authors mentioned, the perimeter flight pattern is similar to the helix flight pattern used for the fixed wing, what is the main reason for the difference in the results measured by the two methods when the wind is greater than 3 m/s?

Point 3: From table 7, the authors expect absolute differences less than 16% in offshore applications, such as the North Sea. Is this measurement accuracy suitable for emission rates less than 3kg/hr?

Point 4: Can the authors provide typical methane emissions in a large offshore oil and gas producing region, such as the North Sea. Or whether the methane release rates offshore are included in the controlled release experiment

Author Response

Thank you for your review.

I addressed the following comments:

1. We added time it takes to complete each flight pattern type in the corresponding section.
2. Fixed wing uses drone derived wind measurements using wind triangle equation/ kalman filters on board. Rotary drones use a ground based anemometer to estimate wind at each height of the surveys and a roughness parameter input. 
3. We have determined a 2.5 kg/h offshore detection limit using the fixed wing drone due to stand off distance. So we would expect the same percent error down to 2.5 kg/h but not less than that. 
4. I added figure 1 to the introduction. 

Reviewer 2 Report

The article is interesting and should be published after minor corrections. In my opinion:

1. Drawings no. 5, no. 9, no. 10 and no. 11 are poorly visible and illegible. Please improve their quality

2. Was the p value determined in the case of regression between metered rate in kg / hr versus detected emission calculated in kg / hr

3. Conclusion was written very briefly. It is worth underlining how important this topic is and what significance is the research carried out.

4. The bibliography is quite limited, can I add scientific publications on topics related to the publication?

Author Response

Thank you for your time reviewing. 

I have addressed the comments as follows:

1. I have updated the figures with new figures with larger text that are more easy to read and interpret.
2. The p value was not calculated. 
3. We rewrote and added to the conclusion making it take the point home fully.
4. We added more literature review to the introduction covering current techniques in the field of methane and carbon emissions. 

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.