A comprehensive review of hybrid-powered drones for long-distance water sampling and in-flight physicochemical analysis insights

Abstract Unmanned aerial vehicles (UAVs) are increasingly employed in environmental monitoring due to their operational flexibility, cost-effectiveness and high spatial resolution. UAV-based water sampling has emerged as a vital approach for the biological and physicochemical assessment of aquatic ecosystems. Although previous reviews have examined water-sampling mechanisms or propulsion technologies independently, a unified and integrated assessment remains absent. This paper presents a systematic review of long-range UAV platforms for water-sampling applications, with particular emphasis on the combined evaluation of water-sampling mechanisms, in-flight physicochemical sensing technologies and hybrid propulsion architectures. The reviewed literature is categorised into three principal areas: UAV-based water-sampling systems, in-flight physicochemical analysis technologies and hybrid UAV configurations, including fuel-cell-powered and other hybrid-propulsion systems. These advances pave the way for sustainable and efficient aerial platforms for water-sampling applications. Finally, the paper identifies key research gaps and outlines potential directions for future innovation in UAV-based water sampling.