Potential of satellite spectral imagery applications for monitoring flexible pavement aging

The efficiency and functionality of road networks deeply influence the economic and social development of a country. In contrast, when road infrastructure no longer fulfills the required standards, it could represent a serious concern in terms of safety of the transportations system. Indeed, during their lifetime, flexible pavements are subject to continuous aging and degradation due to both environmental factors and traffic loads. To maintain a high level of service and safety, it is essential to monitor this phenomenon to ensure timely scheduling of effective maintenance. Traditional monitoring techniques mainly consist in visual inspection of road segments along with different in situ measurements expressing the superficial condition and the bearing capacity of the pavement. Nevertheless, the final assessment of damage is often qualitative and limited to the observation points. In addition, these methods are expensive, labor intensive and time consuming and results inefficient at a large-scale level.

In this context, the use of remote sensing techniques has progressed in recent years as it offers a highly-productive nondestructive method for evaluating road conditions. These new techniques hold many advantages and provide an opportunity for frequent, comprehensive, and quantitative surveys of transportation infrastructures. Remote sensors can acquire the emitted and reflected energies of the target in different parts of the electric spectrum, and they can be used in the identification and characterization of distresses and aging processes of asphalt mixtures. These technologies can be implemented from various platforms, such as UAVs, airplanes and satellites, characterized by different resolutions and used for different applications.

In particular, the use of satellite imagery is remarkably promising as it enables continuous, large-scale observation of flexible pavement networks, with the possibility to have access to historical datasets, thereby allowing a long-term assessment of the pavement conditions. Despite the limited ground resolution characterizing most of multispectral and hyperspectral satellites, the collected imagery enables quantitative monitoring of flexible pavements through analysis of surface reflectance characteristics across visible (VIS), near infrared (NIR), and shortwave infrared (SWIR) wavelengths. In fact, in these regions variations in asphalt reflectance spectra are directly associated with material aging, oxidation, asphalt content reduction and aggregate exposure. It has been found that the reflectance spectrum tends to generally increase over time due to the aging phenomenon. In addition, the loss of hydrocarbons causes the vanishing of the absorption properties at 1700 nm and 2300 nm, while the aggregate exposure results in the appearance of absorption features at 520, 670 and 870 nm. These changes are evaluated by using two main indicators: the VIS2 (830 nm-490 nm) and the SWIR range (2120 nm-2340 nm).

This study reports on the feasibility of using satellite spectral products to monitor the aging of flexible pavements. Following a pro & cons analysis of this survey methodology compared to other techniques, the promising results obtained by an application over three large, paved areas located inside an airfield is presented. This research was conducted within the framework of I4DP_SCIENCE RESCUE_SAT project (Agreement n. 2025-2-HB.0), in collaboration with the Italian Space Agency (ASI).