# Runway Pavement Structural Analysis Using Remote Laser Doppler Vibrometers
## 1 Introduction  
Extended exposure to prolonged heavy loads from both traffic and environmental factors leads to continuous degradation of the structural performance of airfield pavements [1]. Structural analysis is crucial for airfield pavement evaluation and plays a critical role in ensuring airfield operation safety and efficiency [2]. Traditionally, the evaluation of airport pavement structural performance has been divided into two main categories: destructive and non-destructive testing methods [3]. Destructive tests, encompassing core sampling and splitting tensile strength experiments, provide insights into the material and structural properties [4]. While they offer outstanding accuracy, these tests introduce damage and pose safety risks to the pavement structure [5]. On the other hand, non-destructive testing relies primarily on various types of deflectometers. As classified by [PERSON] et al., deflectometers, based on their load application, can be subdivided into static, steady-state, falling weight, and dynamic categories [6]. Of these, Heavy Weight Deflectometers (HWDs), as falling weight deflection measuring equipment, are predominantly selected for gauging airport pavement deflection, which is attributed to their straightforward operation and minimal disruption to pavement structural integrity [7]. Using the deflection bowl information derived from HWD assessments [8], the modulus of pavement structure can be retroactively determined [9; 10; 11], leading to a precise evaluation of pavement structural health. Dynamic deflectometers, such as Traffic Speed Deflectometers (TSD) [12] and Laser Dynamic Deflectometers (LDD) [13; 14], can achieve measurement speeds of up to 90 km/h [15], enabling high-speed continuous structural performancetesting. Nevertheless, these methods encounter challenges, including interruptions in airfield operations, limited coverage of inspection locations, and extensive time required for data collection and analysis [7; 8; 9; 10; 11; 12; 13; 14; 15]. To address the limitations of traditional pavement assessment methods, smart runway technology has been introduced and undergone significant advancement due to the relentless advancements in sensor technology and communication systems [16]. This is achieved by embedding sensors within airport runways to capture the dynamic response of the pavement during aircraft movement [17; 18]. For instance, the U.S. Federal Aviation Administration (FAA) embedded a wide array of sensors at Denver International Airport, including strain gauges and seismic detectors, which were used to monitor strain data and evaluate the structural performance of the pavement [19; 20; 21]. [PERSON] and his associates analyzed the correlation between rigid pavement deflection and temperature shifts based on sensor data from three rigid pavement slabs at Hartsfield-Jackson Airport in Atlanta [22]. Similarly, [PERSON] et al. installed strain gauges on runways at Newark Liberty International Airport to monitor the risk of pavement slippage and shoving failure caused by interlayer delamination [23; 24]. Furthermore, [PERSON] deployed FBG sensors on rigid pavement panels to analyze the relationship between vertical shear strain and bottom tensile strain under load [25]. The U.S. Army Corps of Engineers Research and Development Center implemented earth pressure cells, asphalt strain gauges, multi-depth deflectometers, and other sensors in a runway pavement repair project in 2019 to monitor runway conditions [26]. [PERSON] et al. developed a framework and key technology for smart runways using a variety of embedded sensors [27]. These innovations were implemented in the construction of runways at both Shanghai Pudong International Airport and Chengdu Tianfu International Airport [17; 27].