Method for UAV-based 3D topography reconstruction of tidal creeks

It is common to obtain the topography of tidal flats by the Unmanned Aerial Vehicle (UAV) photogrammetry, but this method is not applicable in tidal creeks. The residual water will lead to inaccurate depth inversion results, and the topography of tidal creeks mainly depends on manual survey. The present study took the tidal creek of Chuandong port in Jiangsu Province, China, as the research area and used UAV oblique photogrammetry to reconstruct the topography of the exposed part above the water after the ebb tide. It also proposed a Trend Prediction Fitting (TPF) method for the topography of the unexposed part below the water to obtain a complete 3D topography. The topography above the water measured by UAV has the vertical precision of 12 cm. When the TPF method is used, the cross-section should be perpendicular the central axis of the tidal creek. A polynomial function can be adapted to most shape of sections, while a Fourier function obtains better results in asymmetrical sections. Compared with the two-order function, the three-order function lends itself to more complex sections. Generally, the TPF method is more suitable for small, straight tidal creeks with clear texture and no vegetation cover.