A Systematic Review of Planning and Routing Strategies for UAV-Based Search and Rescue Operations: Methods, Evidence, and Research Gaps

This paper reports a systematic literature review of planning and routing strategies for unmanned aerial vehicles (UAVs) in search and rescue (SAR). The review followed a documented protocol and is reported according to PRISMA 2020 and PRISMA-S. From 3,642 database records and 96 titles from exploratory searches and the research group's collection, 54 studies were assessed in full text, and 46 primary studies published from 2021 to 2026 were included. Each study was classified by its presence model, detection model, and objective, and by route structure, revisiting, energy, coordination, risk, and validation. Quality, risk of bias, and level of evidence were also assessed. Coverage routing is the largest strategy family (16 studies), and metaheuristics are the most common method class (13). Risk of bias is high in 26 studies, 23 studies are purely synthetic, and only three flew real aircraft. Eight studies build a cell-wise presence map but treat detection as certain, only two calibrate detection against empirical data, and no study places ground risk in the cost of travel. Seventeen studies report an optimality reference, but only six extend it to the application scale. A pooled effect cannot be computed, so 52 observations from 31 studies are synthesized by stratum. Of twelve tracked gaps, seven were narrowed, four were confirmed, and one was maintained. The main gap is the combination of modeling elements. The median study meets three of nine tracked requirements, and the closest study meets eight but keeps closed routes and unbounded revisiting. No multi-vehicle routing formulation has had its predicted detection probability compared with field measurements. This extended version reports the complete protocol and the per-study classifications.