Dai, W.Q.; Li, H.; Chen, X.D.; Xu, F.; Zhou Z.; and Zhang, C.K., 2020. Saltmarsh expansion in response to morphodynamic evolution: Field observations in the Jiangsu coast using UAV. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 433–437. Coconut Creek (Florida), ISSN 0749-0208.Most studies on the biological features and the morphodynamic indications of saltmarshes focused on individual plant groth, such as the stem height and the biomass. However, the understandings of the the planemetric patterns are limited. In this study, UAV (Unmanned Aerial Vehicle)-based observations are conducted in six saltmarsh areas along the Jiangsu coast, China. 3D point clouds, consequent DEM (digital elevation model) and colour orthomosaics are generated using the SfM (Structure from Motion) techniques. We track the variations in the locations of the saltmarsh front as well as the sizes and the distributions of patchs. The saltmarshes are distributed as a whole piece in the landside, while they turn to scattered patches to the sea. We find the locations of the saltmarsh front as a function of bed elevations and season. The area of a single patch is between 0 and 90 m2. The number of the patches increases then decreases from landside to the seaside. For tidal flats in progradation, saltmarsh slowly expands seaward following the sediment accretion. This study highlights the abilities of the drone and the SfM technologies to measure the salt marsh distributions, and further to analyze the geometric characteristics and biomorphodynamics of tidal saltmarsh flats.

Due to challenging conditions of field survey techniques, it is difficult to measure the topography of tidal flats, an important parameter to understanding the evolution and dynamics of the constantly changing zone. This study used remotely sensed sediment moisture estimates to retrieve tidal flat elevation. The method is based on the observation that the intertidal zone is gradually exposed from land to sea at low tide, meaning that higher elevations contain less moisture. Here, we investigate the nature of the relationship between reflectance and moisture content from Landsat Enhanced Thematic Mapper Plus images and the study areas as a proxy for mapping the elevation of an exposed tidal flat surface. Statistical analysis confirmed a negative correlation between moisture and elevation; however, the correlation coefficient was relatively weak, and the slope of the intersecting tidal creek was found to be a crucial factor affecting this relationship. After segmenting the slope to correspond to areas of tidal flat and nontidal flat surfaces, the correlation coefficient of the moisture and elevation increased significantly. A retrieval model was then developed to generate the tidal flat elevations of different slope grades. After verification, the retrieval accuracy of the model was up to 17.3 cm. This research study demonstrated that the remotely sensed moisture method is suitable for monitoring the surface elevation of tidal flats.

Dai, W.Q.; Li, H.; Zhou, Z.; Cybele, S.; Lu, C.Z.; Zhao, K.; Zhang, X.Y.; Yang, H.T., and Li, D.Y., 2018. UAV Photogrammetry for Elevation Monitoring of Intertidal Mudflats. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 236–240. Coconut Creek (Florida), ISSN 0749-0208. Elevation is a significant factor in analyzing the topographical evolution of intertidal mudflats. However, the difficult access to the site due to the muddy sediment and the tidal creeks make the traditional observations more arduous. Unmanned aerial vehicle (UAV) platforms are nowadays a low-cost source of data for surveillance, mapping and 3D modeling. A multi-rotary UAV was set up with a camera to acquire multi-view images of mudflats in the Yancheng Rare Birds Nature Reserve, China. The procedure for deriving 3-D model was based on the Structure from Motion (SfM) algorithm for Mu...

Yang, H.; Li, H.; Gong, Z.; Dai, W., and Lu, S., 2020. Relations between the number of GCPs and accuracy of UAV photogrammetry in the foreshore of the sandy beach. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1372–1376. Coconut Creek (Florida), ISSN 0749-0208.The combination of UAV (Unmanned Aerial Vehicles) and SFM (Structure from Motion) algorithm is an advanced method. This method makes the observations of sandy beaches more efficient and accurate. The DEM (Digital Elevation Model) from this method can encode elevation data and create highly detailed digital terrain models with a root mean square error (RMSE) of only 10 cm. But needing too many GCPs (Ground Control Points) to guarantee the accuracy of DEM is a main drawback of this method. This paper is aimed to solve this problem and assess how the number of GCPs will impact the accuracy of UAV photogrammetry to find the optimum number of GCPs.