Systematic validation of 3D ground-based radars for tracking birds and bats

Grace Chang , Jennifer Pettis Schallert, Stephanie Schneider, Rachael Young, Sharon H. Kramer, Lizette Crooks, Jesse Lewis, Frank Spada

Ground-based radar (GBR) is increasingly used to quantify bird and bat movement in support of ecological studies, environmental monitoring, and collision risk assessment, yet few studies have systematically validated radar-derived tracks against targets with known positions. We evaluated the performance of two commercially available 3D GBRs using controlled drone flights that were designed to simulate biologically relevant movement patterns ranging from straight-line transiting to highly dynamic chasing behavior. Target detection rate, positional deviation, mean absolute positional deviation, and root mean square deviation were computed for radar-derived positions compared to drone positions across horizontal and vertical dimensions. Both radars successfully detected moving targets and produced georeferenced tracks generally consistent with drone positions within tens of meters. Detection performance varied with radar power, flight trajectory relative to radar orientation, and flight track continuity. Flights near the limits of the radar viewshed and behaviors with dynamic maneuvering produced greater tracking variability. Positional discrepancies were primarily driven by georeferencing uncertainty, and track continuity and smoothness. Drone-radar positional discrepancies in the vertical dimension were generally within estimated drone position uncertainties, supporting the use of 3D GBRs to characterize flight height distributions relevant to collision risk modeling. These findings demonstrate that GBR can provide accurate, quantitative bird and bat movement data at spatial and temporal scales difficult to achieve with visual or optical methods alone, while underscoring the importance of careful siting, georeferencing, and conservative interpretation of tracks near radar viewshed limits or during highly dynamic flight behavior. As infrastructure development continues to expand globally, validated GBR systems can strengthen ecological monitoring and support more defensible decisions that balance infrastructure needs with wildlife conservation.