Editorial for Special Issue "Radar Systems for the Societal Challenges"

The special issue (SI) “Radar Systems for the Societal Challenges” is an updated survey of recent advances in radar systems, encompassing several application fields and related to the impact on society. In fact, radar technology is now pervasive in society and is crucial for tackling social and economic issues for the wellbeing of the population. In fact, in addition to the classical application fields, i.e., navigation, air traffic control, and surveillance, emerging applications are now arising, which range from diagnostics and monitoring in civil engineering and cultural heritage, to medical applications, monitoring of environmental parameters, and security in urban areas. These new applications are possible thanks to the improved capabilities of radar systems, accompanied by new advanced modeling and data processing, able to tackle electromagnetically complex scenarios. Most of the works present in this SI can be categorized according to the relevant application fields. The first batch regards the use of radar systems in monitoring for environmental protection; in this area, a recent focus is on sea monitoring and observation, using radar systems on different platforms. In this frame, the first paper from Abileah et al. [1] investigates the possibilities offered by current and future satellite radar altimetry missions for the study of inland water bodies, probing into the peculiarities of the expected radar returns and their potential usage. Two other papers show the use of X-band radar systems for sea state monitoring. The first one presents a comparison between drifter and X-band wave radar for sea surface current estimation [2], while the other aims at improving the operational capabilities of X-band radar systems by performing advanced data processing for wind parameter estimation, starting from X-band radar collected in challenging rainy conditions [3]. The last paper of this batch regards the use of a new observation modality ensured by an X-Band airborne interferometric synthetic aperture radar (SAR) system for sea surface observation [4]. Radar systems are now a significant observational tool in the field of Cultural Heritage monitoring, as shown by the paper from Masini et al. [5], which presents a significant example of integration of ground penetrating radar and electrical resistivity tomography for the archaeological investigation in Kaifeng (Henan, China). In [6], the capabilities of SAR interferometry have been demonstrated for monitoring ground deformation and structural instabilities over the ancient city walls (Ming Dynasty) in Nanjing City, China. Two recent fields of application of radar systems are security and healthcare. For these fields, different radar technologies are now under development and this SI presents a good survey of these research and technological efforts. In particular, good examples of the development and adaptation of the CW Doppler radar to the human detection and activity classification in through-wall configuration and for vital signs monitoring are presented in [7,8], respectively. The paper from Yang et al. [9] deals with the micro-Doppler radar signatures exploitation in order to identify passengers with different baggage, which is helpful to improve the efficiency