Research on airborne relaying in wireless sensor networks explores the use of unmanned aerial vehicles (UAVs), drones, or airborne sensor nodes to act as mobile relays, data collectors, or communication back-haul links for ground or underground sensor deployments. These airborne relays enhance connectivity, address coverage holes, extend network lifetime, and reduce energy consumption for static sensor nodes by allowing short-range transmissions to a moving carrier rather than long multi-hop links. Recent works integrate trajectory optimization, relay position planning, and adaptive scheduling to maximize throughput, minimize delay, and conserve energy under variable link conditions and aerial mobility constraints. They also account for real-world challenges such as path-loss variations, mobility energy cost, and coordination of multiple aerial relays or swarms to support large-scale or hard-to-reach sensing environments.