Detection of Volatile Organic Compounds (VOCs) in Indoor Environments Using Nano Quadcopter

Round 1

Reviewer 1 Report

The paper is very actual and presented results are very important for CBRN community. In my opinion, the paper is ready for publication in current form.

Author Response

We express our gratitude to the reviewers for dedicating their valuable time and expertise to critically assess this work.

Reviewer 1

We sincerely appreciate your thoughtful evaluation of our paper. Your recognition of its topical relevance and the significance of the presented results to the CBRN community is truly encouraging. We value your expert judgment, and your assertion that the paper is publication-ready in its current state is a testament to the effort we have invested in its preparation. Thank you once again for your positive assessment.

Author Response File: Author Response.docx

Reviewer 2 Report

This study is to present the feasibility test of detecting gases in areas that are difficult to access for humans. The paper explained an enhanced odor source detection system using a commercial quadcopter with gas sensor.

The system also requires location measurement system in the given room space. That means the proposed system can be applicable in the closed room space not in the open room space. The authors need to compare the situations between the proposed system and the conventional gas sensor system, which uses many gas sensors on various location in the given space.

The authors also need to present the effect of the rotor wind to the gas concentration measurement of the gas sensor.

Author Response

We express our gratitude to the reviewers for dedicating their valuable time and expertise to critically assess this work. We appreciate your detailed observations about our study.

Reviewer 2

Comment 1:

This study is to present the feasibility test of detecting gases in areas that are difficult to access for humans. The paper explained an enhanced odor source detection system using a commercial quadcopter with gas sensor.

The system also requires location measurement system in the given room space. That means the proposed system can be applicable in the closed room space not in the open room space.

Response 1:

Perfect observation, this study aims to present the feasibility test for detecting gases in areas that are challenging for human access. The article elaborates on an enhanced odor source detection system using a commercial quadcopter with a gas sensor. Additionally, the system requires a location measurement system within the designated room space. This implies that the proposed system is applicable in enclosed spaces, as opposed to open spaces.

Comment 2:

The authors need to compare the situations between the proposed system and the conventional gas sensor system, which uses many gas sensors on various location in the given space.

Response 2:

We appreciate your suggestion and recognize its value for enhancing our study. Information about comparing the situations between the proposed system and the conventional gas sensor system was included in the manuscript on line 40.

Comment 3:

The authors also need to present the effect of the rotor wind to the gas concentration measurement of the gas sensor.

Response 3:

Certainly, the influence of the propellers' movement on the airflow around the gas sensor is indeed a significant issue that requires special attention from researchers in this field. The work conducted by Luo et al. (2016) refers to this problem as the "aerodynamic olfactory effect."

A study by Rossi and Brunelli (2017) proposed an alternative to mitigate the impact of the propellers by suggesting the placement of sensors, both with rigid and mobile supports, on the bottom of the aircraft. However, this solution proved unfeasible due to a substantial alteration in the aircraft's inertia and mass, necessitating counterweights that exceeded the vehicle's payload capacity. Furthermore, another proposal from the study was to use the vehicle in "butterfly mode." While this approach is practical, it significantly increases the testing time and faces limitations on flight time imposed by the aircraft model used in the project. Additionally, the advantage of three-dimensional environmental scanning is wasted as the aircraft needs to land for each measurement.

The study conducted by Burgués et al. (2019) concluded that, indeed, the gas distribution near the drone is drastically altered, but it is still possible to extract relevant characteristics for gas source location. In the study, measurements of gas detection were taken at three different positions relative to a known source: 25 cm above, 65 cm above, and 50 cm in front, with both engines on and off. The results showed that the frequency of detection events increased significantly in the positions above the source and decreased in the front position, while the amplitude decreased in the positions above and remained unchanged in the front position.

Hence, we consider the impact of the propeller wave on odor dispersion when determining the optimal gas sensor placement on the Crazyflie.

Author Response File: Author Response.docx

Reviewer 3 Report

The paper discusses Detection of volatile organic compounds (VOC) in indoor 2 environments using nano quadcopter.

The following are suggestions towards improvements in the paper:

1. The gaps identified through the literature survey could be explicitly written.

2. The contributions and objectives of the paper can be detailed.

3. The methodology of the paper can be described in the form of work flow diagram.

4. The techniques and tools used could be discussed in detail.

5. There could be more observations and inferences drawn based on the results.

6.This could result in concrete conclusions.

Author Response

We express our gratitude to the reviewers for dedicating their valuable time and expertise to critically assess this work. We appreciate your detailed observations about our study.

Reviewer 3

Comment 1:

The gaps identified through the literature survey could be explicitly written.

Response 1:

Based on our literature review, we have identified several significant research gaps. Firstly, previous studies utilizing gas gradient-based plume tracking have not yielded effective results. Furthermore, the research found in the literature requires initial adjustments and complex data processing, demanding significant computational resources and a high level of expertise in data analysis to achieve practical relevance. Most of these works do not provide the ability to quickly and accurately assess the location of odor sources, which represents a considerable gap in the field. Additionally, studies offering real gas reading data from experiments with drones and commercially available sensors are scarce. Moreover, a promising area for exploration lies in the in-depth investigation of the feasibility of using nano quadcopters in enclosed environments for gas leak detection, ensuring that the rotor's motion does not interfere with data collection by the onboard gas sensor.

Comment 2: The contributions and objectives of the paper can be detailed.

Response 2:

The central objective of this article is to enhance the detection of volatile gas leaks in indoor environments using Navigation Autonomous Vehicles (NAVs). In addition to the primary goal, we also have the following specific objectives:

• Analysis and evaluation of the hardware to be used in the project, including the model of the aerial vehicle, the local positioning system, and the chemical gas detection sensor.
• Integration of the sensor into the aircraft and the development of a communication interface between the two.
• Conducting tests to characterize the gas sensor's response.
• Assessment of the data to be extracted from the gas sensor readings to improve odor source localization efficiency.
• Development of the computational algorithm that will guide the aircraft in mapping the environment and declaring the gas source's location.
• Planning of experimental tests and the evaluation of the obtained results.

To accomplish these objectives, we conducted comprehensive experiments involving real-time monitoring and addressing the challenges related to path selection using microquadcopters and commercially available gas sensors. The specific configuration of the aircraft, careful sensor selection, and the strategy for gas release in the environment have proven to be pivotal elements for achieving and strengthening the results obtained. The sensor integrated into the Unmanned Aerial Vehicle (UAV) records environmental data, which is subsequently processed and used to generate reports, enabling real-time and offline air quality analysis in the monitored environment. The technology presented in this research demonstrates particular utility in hard-to-reach areas, such as tunnels or confined spaces housing gas pipelines or storage tanks.

Comment 3:

The methodology of the paper can be described in the form of work flow diagram.

Response 3:

Thanks for the comment, the work flow diagram was included in the manuscript.

Comment 4:

The techniques and tools used could be discussed in detail.

Response 4:

Thanks for the comments. Details about the programs used for autonomous flight and the deck drove to interface the gas sensor with crazyflie 2.1 was included in the manuscript.

Comment 5:

There could be more observations and inferences drawn based on the results.

Response 5:

Thank you for your comment; we have incorporated additional observations and inferences derived from the results.

Comment 6: .This could result in concrete conclusions

Thank you for your comment, conclusion has been improved for the next review.

Author Response File: Author Response.docx

Reviewer 4 Report

There are some suggestions for pictures. First, pictures are not clear enough and all the simulation results need to be vectorgraph. Second,  the physical picture's background is too cluttered. Third, in Figure 4 , the two graphs can be displayed as subgraphs.

The article is not innovative enough. And the article lacks universality, only aocohol is not enough to explain the conclusion, there are supposed to show variety VOC's experimental results.

Author Response

We express our gratitude to the reviewers for dedicating their valuable time and expertise to critically assess this work. We appreciate your detailed observations about our study.

Reviewer 4

Comment 1: There are some suggestions for pictures. First, pictures are not clear enough and all the simulation results need to be vectorgraph.

Response 1: We understand your concerns about the clarity of the images and the format of simulation results. We will review the images to ensure they are sharper and also consider converting the simulation results into vector formats to provide a more precise and readable presentation.

Comment 2: Second,  the physical picture's background is too cluttered.

Response 2: Thank you for sharing your perspective and your observations regarding the background of the physical image. We will review and consider alternatives to improve the clarity of the background, ensuring that it does not distract from the main content.

Comment 3: Third, in Figure 4 , the two graphs can be displayed as subgraphs.

Response 3: We understand your idea of presenting the two figures as subplots, which can enhance the clarity and organization . We are implementing this improvement.

Comment 4: The article is not innovative enough.

Response 4: We appreciate your feedback on our paper. We regret that the perceived level of innovation did not meet your expectations. Our innovation is rooted in the use of experimental tests to enhance the detection of volatile gas leaks within indoor environments, employing Autonomous Navigation Vehicles (NAVs). Our work encompasses real-time monitoring, addressing challenges related to trajectory selection, and the careful selection of the most suitable NAV, as well as commercially available gas sensors.

The research objectives and the advantages of applying UAVs over conventional systems were emphasized in the manuscript to give more visibility to the work's contributions to the scientific community.

Comment 5: And the article lacks universality, only aocohol is not enough to explain the conclusion, there are supposed to show variety VOC's experimental results.

Response 4: Indeed, it is correct, we only tested for alcohol vapor. We value your observation about the need for greater universality in the content, recognizing that the inclusion of a wider range of experimental results for Volatile Organic Compounds (VOC) would be beneficial. However, we believe that gases with similar characteristics, a fluid denser than air like alcohol, would exhibit the same behavior; in other words, we expect the behavior to be similar. Nevertheless, for gases that are less dense than air, it is prudent not to make this generalization.

 We appreciate your valuable contribution and the opportunity to improve our work.

Author Response File: Author Response.docx