A GPS-Free Bridge Inspection Method Tailored to Bridge Terrain with High Positioning Stability
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsPlease see the attached file.
Comments for author File: 
Comments.pdf
Overall, the English is generally good; however, refining some expressions and tightening overly long sentences would further improve clarity and readability.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsSummary:
With the development of drone technology in recent years, many studies have discussed how to leverage drones equipped with sensors and cameras to conduct inspections un-der bridges. To address positioning challenges caused by the lack of GPS signals under the bridges, triangulation methods with on-site pre-installed UWB sensors were used extensively to determine drone locations. However, the practical hurdles of deploying anchors under bridges are often overlooked, including variable terrain and potential electromagnetic interference from deploying a large number of UWB sensors. This study introduces a handover mechanism to address long-distance positioning challenges and an improved two-stage algorithm to enhance its suitability for bridge terrain with higher stability. By integrating these concepts, a practical bridge inspection system was devised, and realistic under-bridge experiments were conducted to validate the method's efficacy in real-world settings.
Comments(Minor):
1. Please explain more about how to settle UWB, and what kind of rules you are matching? Please add the explanation in the caption of Figure 3. What is UWB short for?
2. What models did you use in Figure 4? Object detection and Mask segmentation.
3. Please explain what software you are using in Figure to photogrammetry or 3D-reconstructure?
4. What is DUT short for?
5. Please match the title font format.
6. Please do not add the reference 28 and 32 at the starting of the paper, even they are highlights.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors
This manuscript takes on an important and very practical challenge: how to carry out UAV-based bridge inspections in places where GPS signals aren’t available. The authors propose a system that combines UWB anchors with a handover mechanism and an enhanced two-stage SVD positioning algorithm. The real bridge experiments add credibility to the work, and the use of AI for defect detection within a management platform makes the approach even more useful. Overall, I see this as a valuable contribution to the field of robotic inspection, and I recommend it for publication once the authors address the points outlined below.
- Experiments on two bridges are commendable, but the validation seems limited to a small number of test scenarios. Were tests conducted under varying conditions (e.g., strong wind, occlusions, moving traffic, multipath interference)?,
- The RMSE results are given, but the robustness of the system is not deeply analyzed. For example, what happens when UWB signals are obstructed by beams or vehicles?
- The experiment for the handover mechanism was conducted with an experimenter carrying the tag. While this proves the concept, it would be valuable to see the same experiment conducted with the drone in flight to account for factors like wind and flight dynamics, which are a part of the actual application.
- For Bridge B, 27 anchors were used for 166 m length. What would be the scaling requirements for bridges of several kilometers, as suggested in the highlights? Additionally, maybe, a cost and logistics discussion would help practitioners assess feasibility.
- Was any evaluation metric (e.g., mAP, precision-recall) reported for the defect detection performance?
- How sensitive is the positioning accuracy to anchor placement errors (e.g., RTK errors or misalignments)?
- Did you compare (if possible and logical) the enhanced two-stage method with SLAM or sensor fusion approaches in similar scenarios?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
