Sheet erosion is an important process in soil degradation and surface soil loss, but quantification remains difficult because soil is removed in a thin layer. In this study, we tested a method for tracking sheet erosion at high temporal resolution by combining Structure-from-Motion (SfM) with time-lapse cameras capable of nighttime imaging and a colored surface-soil tracer. A study plot measuring 7.5 m in width and 10 m in length was established, and white tracer lines were applied. Images were acquired at 30-min intervals from 24 August to 6 November 2025. Daytime and nighttime orthomosaics were generated using a UAV-derived digital elevation model (DEM) and camera position and orientation data. A sheet erosion index, E, was derived from temporal changes in normalized tracer brightness. Nighttime images acquired in infrared mode allowed identification of the white tracer lines and tracking of their temporal changes even with few tie points. During non-rainfall periods, the standard deviation of normalized tracer brightness showed positive relationships with solar radiation and negative relationships with relative humidity during daytime, whereas no clear relationships with meteorological variables were observed at night. This indicates that nighttime observations under infrared imaging were less affected by meteorological conditions and allowed more stable tracer detection. In addition, E showed strong relationships with rainfall duration and total rainfall, but weak relationships with rainfall intensity and microtopographic conditions. Although the proposed method does not directly quantify absolute erosion, it has potential for relative assessment of sheet erosion dynamics, especially under stable nighttime conditions.