This study presents, for the first time, high‑resolution concurrent vertical profiles of temperature, humidity, water vapour, and fog/cloud droplet microphysics during a stratus‑fog‑stratus transition over the Yellow Sea (15–16 May 2025). The primary observational platform relied on a novel Lightweight Cloud Particle Imager sonde (LCPIS) deployed on an unmanned aerial vehicle (UAV) system. The event progressed through three distinct stages: pre‑fog stratus, dense fog (minimum visibility ~100 m), and lifting to stratus. Pre‑fog stratus featured a shallow mixed layer (<em>Ri</em> < 0.25) capped by a strong inversion (<em>Ri</em> > 0.25), trapping moisture below 300 m. During the fog transition, the inversion base stabilized at 270 m with a lapse rate of 5.0 °C·(100 m)⁻¹, while the saturated layer extended to the surface. Within the fog layer, the Richardson number (<em>Ri</em>) was negative, indicating vigorous turbulent mixing, while <em>Ri</em> > 0.25 near the fog top formed a dynamically stable cap. After dissipation, <em>Ri</em> turned positive and evaporated moisture re‑formed stratus. Peak droplet number concentration (<em>NC</em>) increased from 50–100 cm<sup>-3</sup> (pre‑fog) to 100–120 cm<sup>-3</sup> (fog), liquid water content (<em>LWC</em>) doubled from 0.1–0.2 to 0.2–0.45 cm<sup>-3</sup>, and mean diameter ranged 10–20 μm. Microphysical peaks occurred at ~200 m in both pre‑fog and fog stages. Key transition indicators include downward extension of the saturated layer to the surface, rise of the zero dew‑point depression height, and <em>NC</em> stabilization with <em>LWC</em> increase. This study provides the first synchronized vertical observations of thermodynamic, water vapour and microphysical parameters during a stratus-fog-stratus transition, offering a robust observational basis for improving sea fog forecasting.