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High temporal frequency monitoring of transport infrastructures is crucial for implementing effective maintenance prioritisation strategies and prevent major failures. To this extent, ground-based non-destructive testing (NDT) methods have been successfully applied for decades, reaching very high standards of data quality and accuracy. However, routine and systematic campaigns are required over relatively long inspection times for data collection and implementation into reliable infrastructure management systems (IMSs). On the other hand, satellite remote sensing techniques, such as the Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) method, have proven effective in monitoring ground displacements of transport infrastructures (roads, railways and airfields), with a much higher temporal frequency of investigation and wider inspection catchment areas. Nevertheless, the integration of information from i) satellite remote sensing and ii) ground-based NDT methods is still an area to be explored in civil engineering. Within this framework, this paper aims to review significant stand-alone applications in these two areas of technology for transport infrastructure monitoring. Furthermore, recent advances, main challenges and future perspectives arising from their integration are discussed. Contents of this paper are organised within the context of an invited keynote talk given at the 2021 IEEE Asia-Pacific Conference on Geoscience, Electronics and Remote Sensing (AGERS – 2021).

Railways are important assets requiring continuous and effective monitoring. Within this context, non-destructive testing (NDT) methods are gaining momentum including, amongst others, the ground-penetrating radar (GPR) technique. GPR has proven its viability at providing effective condition-based assessment of railway ballast and identifying several different sources of decay. In this paper, the main challenges related to the data collection and processing stages for railway ballast investigations are reported. In addition, a review of main survey protocols and data processing strategies, including state-of-the-art research in this area of endeavor is presented, in terms of the issues related to the configuration of the track-bed structure (i.e., the effects of rails and sleepers on the signal) and the main inspection targets (i.e., ballast fouling, water content and segregation of the aggregates).

Early-age cracking is a major issue in design and construction of concrete pavements. This occurrence depends upon various factors i.e., design features, concrete mixture materials, jointing techniques, and environmental circumstances. This may however occur despite adequate design, construction, and jointing operations are correctly followed. Interactions of the above key factors are assessed using comprehensive analytical methods which are demanding in terms of data input and computational requirements. This research presents a streamlined probabilistic methodology for probabilistic risk assessment of early cracking in airfield concrete pavement design. The method provides a strength-to-stress ratio (SSR) index for identification of critical cracking conditions. A risk chart is presented with reference to the designed SSR value, and the required reliability level of the design process.

Deformations monitoring in airport runways and the surrounding areas is crucial, especially in cases of low-bearing capacity subgrades, such as the clayey subgrade soils. An effective monitoring of the infrastructure asset allows to secure the highest necessary standards in terms of the operational and safety requirements. Amongst the emerging remote sensing techniques for transport infrastructures monitoring, the Persistent Scatterers Interferometry (PSI) technique has proven effective for the evaluation of the ground deformations. However, its use for certain demanding applications, such as the assessment of millimetric differential deformations in airport runways, is still considered as an open issue for future developments. In this study, a time-series analysis of COSMO–SkyMed satellite images acquired from January 2015 to April 2019 is carried out by employing the PSI technique. The aim is to retrieve the mean deformation velocity and time series of the surface deformations occurring in airport runways. The technique is applied to Runway 3 at the “Leonardo da Vinci” International Airport in Rome, Italy. The proposed PSI technique is then validated by way of comparison with the deformation outcomes obtained on the runway by traditional topographic levelling over the same time span. The results of this study clearly demonstrate the efficiency and the accuracy of the applied PSI technique for the assessment of deformations in airport runways.

Use of non-destructive testing (NDT) methods has tremendously increased over the last decades in a wide range of civil and environmental engineering applications. Research on stand-alone use of electric, electromagnetic, optical and acoustic NDT techniques has rapidly progressed and potentials of these methods have been comprehensively explored and evaluated, making the majority of techniques established in many areas of endeavour. Research focus areas have been mostly on developing new theories, the advancement of hardware and software components, and on introducing novel surveying protocols, data processing and interpretation methods. Accordingly, the standard of quality and accuracy of data has reached very high levels with available technology.\ud Parallel to this, the integration between sensing technologies, in terms of collecting and modelling multi-source, multi-scale and multi-temporal data, has become a very challenging task in research. This concept is in fact being acknowledged as a fundamental area of research development that could highly contribute towards the enhancement of the capabilities of existing NDT methods in new and non-conventional scenarios. This trend is motivated by the need to provide more effective solutions for the investigation of complex scenarios. At the same time, a balance among project costs and time requirements on one hand, and resource management-related constraints due to the involvement of multiple methods, equipment and interdisciplinary expertise in the other, must be maintained.

Applications of non-destructive testing methods such as ground penetrating radar (GPR), 3D laser scanners, accelerometer sensors and vibration detecting sensors amongst many others have been used to assess and monitor masonry arch bridge spans (brick and stone) in the past few years. This paper reports the application of high to low frequency GPR antenna systems (2000 MHz, 600 MHz and 200 MHz) and a 3D laser scanner on a historic masonry arch bridge (the Old Bridge, Aylesford - 860 years old) located in Kent, England. The position of different layers of the deck structure was established with the identification of the original stone base of the bridge and location of a number of structural ties (anchors – remedial work carried out previously). Results of the 3D laser scan of the bridge were crucial to initiate long-term monitoring of the structure.

Deicing and anti-icing operations are frequently carried out on aircrafts at their current parking stand after completion of ground operations. Use of individual stands can be often challenging as this may also considerably affect operations, especially in highly-trafficked airports at winter-critical areas. Hence, a lack of or an incorrect location of these stations may have tremendous economic and operational impact. This research reports a multi-stage design method for construction of a 29,000 m2 deicing station in a critical soil site. The main aim of the project is to identify sustainable interventions in order to avoid short- A nd long-term economic, environmental, and operational issues. An assessment based on the use of fundamental geotechnical parameters is first implemented to create thematic maps of the identified construction area, followed by a comparative analysis of potential intervention scenarios. A combination of lightweight filling and advanced materials has been proposed to ensure homogeneity and suitable bearing capacity of the laying ground.

This work proposes an experimental-based model for the assessment of the stiffness of a road flexible pavement using ground-penetrating radar (GPR – 2 GHz horn antenna) and light falling weight deflectometer (LFWD) non-destructive testing (NDT) methods. It is known that the identification of early decay and loss of bearing capacity is a major challenge for effective maintenance of roads and the implementation of pavement management systems (PMSs). To this effect, a time-efficient methodology based on quantitative and qualitative modelling of road stiffness is developed. The viability of using a GPR system in combination with LFWD equipment is also proven.