Ocean surface water currents by large-scale particle image velocimetry technique

摘要

This study investigates the capability of camera technology and Large Scale Particle Imaging Velocimetry (LSPIV) measurement techniques to access the sea surface velocity conditions in spatiotemporal dimensions in a tidal inlet, located in the southern North Sea. LSPIV shows reliable results for various applications in riverine and hydrographic studies, nonetheless LSPIV is up to date less prominent in offshore maritime studies. Characterized by high dynamic velocity ranges, changing water levels, waves and directions of flow within tidal cycles, the maritime domain implies varying boundary conditions compared to inland study areas. We present application possibilities, procedures as well as computer vision and data fusion approaches based on remote sensing in the oceanographic environment. Video data of the sea surface, observed from high-resolution visual camera, are analyzed for natural tracers within tidal cycles. Quality assessments were applied for prevailing environment conditions as well as concurrent observations with an Acoustic Doppler Current Profiler (ADCP) and current meter in the water column for hydrographic conditions. The LSPIV method showed reliable results for the fluctuation of water flow direction. Velocity mean magnitudes permitted to access surface flow for a dynamic range of 0.15-1.5 m/s. Comparing LSPIV and in situ measurements, we achieved deviations in the range of ± 0.5 m/s within a tidal cycle and with a good correlation (R² = 0.82) given appropriate light conditions. The optical method applied here within offers a complementary alternative for modern environmental monitoring enabling space- and time-resolved hydrographic information for the oceanographic research domain.