## 2 Study Area and Materials  
The large (about 500 km\({}^{2}\)) Tiaozini tidal flats are located in the core intertidal area of the Radial Sand Ridges (RSRs) of the Jiangsu coast, China. The widths of the tidal flats here are about 14-20 km, and the slope is only 5%\(\infty\)-10%o [3]. The RSRs are controlled by a large-scale tidal wave system that is determined by the land boundaries of China and the Korean Peninsula. The tidal wave first enters the Southern Yellow Sea, and part of the wave is reflected by the Shandong Peninsula, forming an anticlockwise rotational tidal wave system. The rotational wave meets the following progressive wave from the southern Yellow Sea, resulting in the formation of large-scale fan-shaped sand ridges [26]. The tidal water from both north and south meet in Tiaozini every day, forming the largest tidal range. The maximum tidal range (9.39 m) was observed for the south channel Tiaoyugang in Tiaozini [27]. Due to such a complex hydrodynamic environment, these tidal creeks (Xidagang, Dongdagang, and Tiaoyugang in Figure 1) swing violently [28; 29]. Based on a comparison of the before-and-after remote sensing images, the amplitude can reach 3-5 km over half a year. The tidal Creek migration inevitably leads to geomorphic changes. In addition, the reclamation activity in this area (completed for 67 km\({}^{2}\) (Figure 1)) inevitably exerts a profound impact on the surrounding environment, such as the geomorphology, the dynamic conditions, sediment transport mechanisms, biotic habitat, etc. [4]. In order to effectively assess and support the impact of reclamation activities, the topographic monitoring of tidal flats is urgently needed.  
This study collected 18 HJ-1A/B charge coupled device (CCD) images and three Landsat images acquired at different tidal stages from 31 December 2013 to 28 May 2014 [13]. These images were used to construct the initial DEM via the waterline method. The remote sensing images are HJ-1 CCD data that have a nadir pixel resolution of 30 m, a width of view of 360 km, and a temporal resolution of two days [30]. Four bands are B1 (0.43-0.52 um), B2 (0.52-0.60 um) and B3 (0.63-0.69 um), and B4 (0.76-0.90 um). In particular, the 21 March 2014 HJ-1 image (Table 1) under the lower tidal conditions and [PERSON]'s initial DEM acquired by the waterline method were input into an ANN simulation model as training data. Two other images (11 February 2012 and 11 July 2013) (Table 1) were applied as test data for the ANN model to simulate the corresponding DEMs at the same time. All the HJ-1 images are clear under good atmospheric conditions. A topographic map (1:50,000) of the Jiangsu coastal zone was collected for geometric rectification of these HJ-1 satellite images. The correct accuracy was controlled within a pixel. A QUAC (QUick Atmospheric Correction) [31] of the HJ-1 images was also carried out in this study. This method provides the automated atmospheric correction of the reflective spectral region (0.4-2.5 um) in the ENvironment for Visualizing Images (ENVI) software (Exelis VisualInformation Solutions, Inc., Boulder, CO, USA) and creates an image of the retrieved surface reflectance, scaled into two-byte signed integers using a reflectance scale factor of 10,000. QUAC was carried out in the ENVI software Toolbox using the following steps: QUAC initiation, radiometric correction, atmospheric correction, and quick atmospheric correction. Two real-time tide stations (Dongdagang and Xintaoyugang) were established around the north and south sides (Figure 1). The tidal level data were applied to the assignment of these waterlines. Three measuring sections in February 2012 and July 2013 were collected to evaluate the accuracy of the DEMs simulated by the ANN model. The Chinese National Height Datum 1985 (CNHD 1985) was adopted for the tide stations, sections, and DEMs. The coordinate system was WGS_1984_UTM_Zone_51N in ArcGIS software.