Muddy intertidal flats are important resources for coastal development activities, such as coastal shoal reclamation and mudflat cultivation. Understanding changes in intertidal flat topography is essential for intertidal zone development, management, and protection. As an essential topographic factor, the slope of an intertidal flat can effectively express profile morphology in the cross-shore direction, reflect topographic undulation in the long-shore direction, and be indicative of intertidal flat erosion and deposition. Previously, intertidal flat slopes have been estimated by the two-temporal average gradient (TTAG) method using two spatially separated waterlines derived from satellite remote sensing data and their relevant water elevations. However, this method does not adequately reflect the profile morphology of different coastline types, especially sinuous coastlines, and is highly sensitive to the selected waterlines. This study proposes an effective strategy for estimating slope considering not only the characteristics of the vertical terrain undulation but also the horizontal plane-form shape of the coastline. Using waterlines extracted from sequential satellite images and their corresponding tidal height information, the slopes were estimated utilizing a profile morphology discriminant inferential (PMDI) method on straight coasts and a digital elevation model (DEM) method on sinuous coasts. We obtained the following results: (a) for straight coasts, by judging the various shapes of the coastal profiles and curve-fitting separately, the PMDI method achieved significant improvements in accuracy and robustness of slope estimates compared to results obtained using the TTAG method; and (b) for sinuous coasts, the DEM-based method performed better for addressing the intersecting waterline issue and accurately retrieved the slope, although this accuracy is strongly dependent on the areal coverage of the DEM and the precision of the terrain inversion. Using this new paired methodology, we estimated that the average slope of the intertidal flats in the Mid-Jiangsu Province between the Sheyang Estuary, the Liangduo Estuary, and the Lianxing Port was 0.96‰. In general, the slopes from north to south in this coastal area exhibited a steep-gentle-steep pattern, which was consistent with in situ observed data. We conclude that stratifying the coastlines according to their plane-form shapes and applying different methods to straight and sinuous coastlines can result in a more robust estimation of coastal slope for muddy intertidal flats than previous TTAG methods. This work demonstrates the utility of satellite-based remote sensing for retrieving critical coastal geomorphological information in dynamic terrains where in situ data are difficult to obtain.

潮间带泥泞的公寓是沿海开发活动的重要资源，例如沿海浅滩填海和滩涂养殖。了解潮间带平坦地形的变化对于潮间带的开发，管理和保护至关重要。作为一个重要的地形因素，潮间带的坡度可以有效地表达跨岸方向的剖面形态，反映长岸方向的地形起伏，并指示潮间带的侵蚀和沉积。以前，潮汐平面坡度已通过两时平均梯度（TTAG）方法进行了估算，使用了两个从卫星遥感数据及其相关水位中得出的空间上分离的水线。但是，这种方法不能充分反映不同海岸线类型的剖面形态，特别是蜿蜒的海岸线，并且对选定的水线高度敏感。这项研究提出了一种有效的估算坡度的策略，不仅要考虑垂直地形起伏的特征，还要考虑海岸线的水平面形状。使用从连续卫星图像中提取的水线及其相应的潮汐高度信息，使用直线形态上的剖面形态学判别推断（PMDI）方法和蜿蜒海岸上的数字高程模型（DEM）方法估算坡度。我们获得了以下结果：（a）对于直海岸，通过分别判断海岸轮廓的各种形状和曲线拟合，与使用TTAG方法获得的结果相比，PMDI方法在坡度估计的准确性和稳健性方面有了显着提高；（b）对于曲折的海岸，基于DEM的方法在解决相交的水线问题和准确提取坡度方面表现更好，尽管该精度很大程度上取决于DEM的面积覆盖范围和地形反演的精度。使用这种新的配对方法，我们估计射阳河口，凉多河口和连兴港之间的江苏省中部潮间带平均坡度为0.96‰。通常，该沿海地区从北向南的坡度表现出陡峭-温和陡峭的格局，这与现场观测数据一致。我们得出的结论是，根据海岸线的平面形状对海岸线进行分层并将不同的方法应用于笔直和弯曲的海岸线，可以比以前的TTAG方法更可靠地估计潮间带泥滩的海岸坡度。这项工作证明了基于卫星的遥感在难以获取原位数据的动态地形中检索关键的海岸地貌信息的实用性。