Research of a Fiber Sensor Based on Fiber Bragg Grating for Road Surface Monitoring

Round 1

Reviewer 1 Report

This paper presents a road surface monitoring approach using fiber optics sensors (FOS). Such sensor technologies allow measuring stress, deformation, deflection, humidity, traffic characteristics, temperature, which directly affect the reaction of the pavement under loads caused by vehicles and the environment. I have a few comments and suggestions that may help improve the clarity and impact of the research paper:

1. Real-time monitoring of road surface is a powerful tool for assessing road infrastructure conditions. Using built-in sensors is usually expensive and can only provide road surface information on a fixed location. In a recent paper “Real-time identification system of asphalt pavement texture based on the close-range photogrammetry”, an ACRP system was developed to provide real-time pavement surface information. The authors are encouraged to discuss this paper and compare built-in sensors with image-based monitoring approaches in terms of accuracy, efficiency, and application scenarios.

2. The durability and resilience of the fiber optics sensors remain unclear. What is their expected lifespan under typical conditions? How well do they withstand heavy traffic loading, a factor that is often a crucial consideration in road surface monitoring? Furthermore, it would be beneficial to know the operational temperature range of these sensors. Providing these details will offer a clearer picture of the practicality and robustness of the proposed system.

3. The paper could delve deeper into the data management aspect of the system. Specifically, how is the data collected by the fiber optics sensors stored, and how is it transferred for analysis? Given the proliferation of wireless technology, it would be interesting to know if there is a provision for wireless data transfer from the sensors to the computer or a central data repository. Such information would significantly add to the comprehension of the system's operation and data handling capabilities.

4. Lastly, it would be beneficial to discuss potential practical applications of this sensor technology in the field. For instance, how might these sensors be integrated into existing infrastructure? What are the specific challenges that could be encountered during such an application, and how might they be addressed? This will not only enhance the real-world relevance of your research but also potentially provide a roadmap for future studies in this area.

The paper contains occasional grammatical errors and typos. These can distract the reader and may affect the overall readability of the paper. It is recommended that the authors proofread the paper thoroughly or consider employing a professional language editing service to correct these mistakes.

Author Response

Response to Reviewer 1 Comments

 

1. In the research paper [4], the authors propose In order to obtain the asphalt pavement texture information in real time and accurately monitor the anti-skid performance of the road pavement, an automatic close-range photogrammetry system (ACRP System) was proposed and established based on the three cameras close-range photogrammetry (CRP) technology. Automatic image acquisition and 3D reconstruction were achieved by the ACRP system. By setting up an automatic close-range photogrammetry platform to fix the positions of three cameras, the camera parameters can be acquired as known values for the following texture reconstruction work. Thus, the camera calibration process can be omitted so that the efficiency of the entire process is improved. In addition, the shadowless light source effect is introduced to eliminate the possibly exists shadow. By adjusting the camera pitch and the depression angle, the asphalt pavement texture information would be completely covered by the three cameras, which ensures the accuracy of the following texture reconstruction. Sand patch testing method and laser scanning method (ZGScan) were used to collect the on-site data as comparison test of the asphalt pavement texture.

This proposed method can be also used in real-time identification of pavement texture information and the establishment of high precision map, both of which have positive impacts on the braking and driving safety of the autonomous vehicles.

 

2. Since we know that the road surface consists of asphalt concrete mixtures and gravel with different particle sizes and, thus, are considered inhomogeneous structures, it is quite difficult to develop an accurate theory and numerical methods to describe the inhomogeneity of these mixtures, and the theoretical and experimental results obtained do not always correspond to each other. The uncertainty of the composition of the asphalt concrete mixture, the temperature sensitivity and viscoelastic characteristics of road materials affect the characteristics of sensors and the accuracy of measurement, which, in turn, affects the assessment of the characteristics of the road surface. The fiber sensor based on FBG is difficult to integrate directly into the road surface due to the rigid construction of the road surface and operating conditions due to the risk of damage to the optical fiber. FBG are quite fragile and can easily break under any load. To increase the reliability, elasticity and durability of sensors based on FBG for road surface monitoring, usually packed in one or more protective packaging layers.

There are numerous studies of methods of packaging fiber sensors and sensors based on FBG, including steel rod [31], fiber-reinforced polymer (FRP) [32], steel sheet [33], bending device [34], pipe [35], polypropylene (PP) [36], glue [37], geotextiles [38] and cables [39].

In this work, gratings with organic modulation and ceramic coating were used for proper protection, embedded in a round profile made of fiberglass-reinforced plastic, which guarantees the accuracy of measurements of both deformations and temperature.

The sensor's operating temperature range is -40 °C to +80 °C

3. A the interrogator system of fiber sensors was used to collect data on deformation and temperature. By relatively long data collection and calculations, we obtain a curve of temperature and strain dependence. An interrogator for fiber Bragg gratings (optical signal measuring converter) is a device that combines software and hardware and fiber–optic means and provides the creation of a luminous flux, analysis and control of spectral characteristics, control and conversion of optical parameters into a measurable value using special algorithms. The interrogator creates a connection with the top-level control systems, serves as the basis for the creation of a new generation of monitoring systems. The interrogator serves as a key instrument of measurement systems based on fiber sensors, simultaneously registering the readings of each of the connected sensors and transmitting the measured readings to top–level devices (in the simplest case, the operator's server). The interrogator is manufactured in several versions and can work with fiber sensors based on FBG. The interrogator was created at Lublin Technical University. The general concept of the fiber optic sensor polling system is shown in Figure 4.

Figure 4 – General concept of the fiber sensor interrogator system

 

The schematic block diagram of the entire interrogator system is shown in Figure 5.

Figure  5 –  Schematic block diagram of the entire interrogator system

 

Various configuration options of the interrogator systems using FBG are shown in Figure 6.

a)

b)

c)

Figure 6 – Various configurations of the interrogator systems a) and b) using conventional fiber sensors based on FBG  c) using optical sensors based on tilted fiber Bragg grating

4. Since the research was conducted in laboratory conditions, practical applications of sensor technology in the field will be considered in the following studies and publications. When installing a fiber sensor in the field, you can follow the following recommendations:

– accurate and careful installation in the asphalt layer is necessary to obtain accurate results;

– preservation of sensors based on the FBG in the process of laying in the asphalt layer, special protection is needed from very high asphalt temperatures and from heavy loads on the seal;

– to ensure the accuracy of measurements, it is necessary to exclude voltage deviation, i.e. to level the surface where we install the sensor;

– to obtain reliable data and improve the monitoring of the condition of the pavement, it is possible to provide for the installation of sensors of various layers of asphalt (surface layer, base layer);

– to avoid signal loss when pulling up, cables must be connected together;

– the asphalt mixture should be laid so that the intensity of the coating is not too high to protect the sensors from severe operating conditions. The road surface must be compacted without vibration.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Based on the overall quality of this study, a major revision is needed.

Comments:

(1) Introduction. What is the research gap? Please clarify it.

(2) Highlight your contribution and novelty in the introduction,

(3) Please summarize the common methods of Structural Health Monitoring (SHM) Methods for pavement in the introduction and compare them to fiber sensors. You can learn it from "Field investigation and numerical analysis of an inverted pavement system in Tennessee, USA."

(4) How can you keep your sensors within the pavement alive?

(5) Any improvement of the fiber sensors from you to sense the pavement structural health？

(6) Please improve the conclusions. Clarify your conclusions point by point.

The language should be polished.

Author Response

Response to Reviewer 2 Comments

1. The uncertainty of the composition, temperature sensitivity and viscoelastic characteristics of road materials make the structural analysis of the pavement very difficult compared to other civil structures, such as bridges, tunnels and buildings. For this reason, the question arose of improving the fiber sensor based on the fiber Bragg grating (FBG). The novelty of this study is to modernize the fiber sensor based on FBG so that it displays deformation, stress and displacement, temperature and other parameters with much greater accuracy, which would provide a reliable scientific basis for modifying the theory. As well as the use of a fiber sensor based on FBG for simultaneous measurement of deformation and temperature when monitoring the road surface.
2. Various types of sensors can also be used to monitor road surfaces in real time. Different kinds of sensors can be used to monitor pavements. They can be classified in two categories: electrical sensors and optical fiber sensors. Classical electrical sensors used for pavement instrumentation include displacement sensors, used to measure vertical displacements, strain gages, used to measure horizontal strains in bound pavement layers, temperature probes, and pressure cells, used to measure vertical stresses or pressures in unbound pavement layers. Fiber sensors have more attractive advantages compared to traditional sensors. Embedded fiber sensors usually cost a lot and provide information about the road surface only in fixed places, but taking into account all the advantages of fiber sensors can be used as an effective means for monitoring. In this paper, the sensory method of monitoring road surfaces is considered.

 

3. In the research paper [4], the authors propose In order to obtain the asphalt pavement texture information in real time and accurately monitor the anti-skid performance of the road pavement, an automatic close-range photogrammetry system (ACRP System) was proposed and established based on the three cameras close-range photogrammetry (CRP) technology. Automatic image acquisition and 3D reconstruction were achieved by the ACRP system. By setting up an automatic close-range photogrammetry platform to fix the positions of three cameras, the camera parameters can be acquired as known values for the following texture reconstruction work. Thus, the camera calibration process can be omitted so that the efficiency of the entire process is improved. In addition, the shadowless light source effect is introduced to eliminate the possibly exists shadow. By adjusting the camera pitch and the depression angle, the asphalt pavement texture information would be completely covered by the three cameras, which ensures the accuracy of the following texture reconstruction. Sand patch testing method and laser scanning method (ZGScan) were used to collect the on-site data as comparison test of the asphalt pavement texture.

In [4], the authors propose two methods for obtaining information about the texture of the pavement: the contact measurement method and the non-contact measurement method. Contact measurement refers to field test using traditional equipment, including sand patch testing method (volume method), outflow meter method (drainage method), British pendulum tester method, dynamic friction tester method, GripTester method, et al. Non-contact measurement method mainly includes digital gray image method, industrial CT scanning method, laser measurement method, close-range photogrammetry (CRP) method, et al. These methods all involve digital reconstruction of 3D model of pavement surface texture. 

 

4. Since we know that the road surface consists of asphalt concrete mixtures and gravel with different particle sizes and, thus, are considered inhomogeneous structures, it is quite difficult to develop an accurate theory and numerical methods to describe the inhomogeneity of these mixtures, and the theoretical and experimental results obtained do not always correspond to each other. The uncertainty of the composition of the asphalt concrete mixture, the temperature sensitivity and viscoelastic characteristics of road materials affect the characteristics of sensors and the accuracy of measurement, which, in turn, affects the assessment of the characteristics of the road surface. The fiber sensor based on FBG is difficult to integrate directly into the road surface due to the rigid construction of the road surface and operating conditions due to the risk of damage to the optical fiber. FBG are quite fragile and can easily break under any load. To increase the reliability, elasticity and durability of sensors based on FBG for road surface monitoring, usually packed in one or more protective packaging layers.

There are numerous studies of methods of packaging fiber sensors and sensors based on FBG, including steel rod [31], fiber-reinforced polymer (FRP) [32], steel sheet [33], bending device [34], pipe [35], polypropylene (PP) [36], glue [37], geotextiles [38] and cables [39].

In this work, gratings with organic modulation and ceramic coating were used for proper protection, embedded in a round profile made of fiberglass-reinforced plastic, which guarantees the accuracy of measurements of both deformations and temperature.

5. The developed fiber sensor based on FBG in combination with the technology of far infrared sensors, both for simultaneous determination of temperature and deformation, and for synchronous determination of temperature and pressure. The results obtained from the sensors showed that the change in displacement as a percentage with respect to the wavelength varies for 5 temperature values from -40 to 80℃, which proves that the displacement changes linearly and proportionally to the wavelength, and this is due to the plasticity of the fiber, which increases with increasing temperature and increases moisture in the fiber, therefore, the offset decreases
6. For durability, elasticity and accuracy of strain measurement during the experiment, a fiber sensor based on FBG with a ceramic coating embedded in a round profile made of glass-fiber reinforced plastic was used.

A the interrogator system of fiber sensors was used to collect data on deformation and temperature. By relatively long data collection and calculations, we obtain a curve of temperature and strain dependence.

The results of the study showed that the synchronicity, repeatability and linearity of the characteristics of the fiber sensor are excellent. The difference between the experimental and theoretical results is about 7%.

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

My comments have been well addressed by the authors. Thanks.

Reviewer 2 Report

Thank you!