Low-Altitude sUAS Flights for Remote Sensing of Submillimeter Hairline Cracks: A Case Study

Abstract

Recent advancements in small uncrewed aircraft systems (sUAS) have enhanced their use in infrastructure monitoring, targeting distresses such as cracks, spalling, delamination, rutting, and rust. While automatic sUAS flights are typically operated at 15–30m altitudes with RGB sensors (12 to 61 megapixels), capturing visible distresses, detecting submillimeter hairline cracks remains challenging. This study explores the feasibility of achieving submillimeter-resolution orthophotos from low-altitude sUAS flights to detect hairline cracks on bridge decks. Data were collected from two bridge decks: a newly constructed deck with hairline cracks averaging 0.25mm in width and a one-year-old deck with grooved cracks (0.35–0.7mm) at altitudes of 4.6m, 10.7m, and 12.2m. Findings show that while low-altitude sUAS flights are challenging to execute, the processed orthophotos provide sufficient resolution for fine crack detection, extending their potential in high-precision infrastructure inspections.