# Analysis of Coastal Zone Data of Northern Yantai Collected by Remote Sensing from 1990 to 2018
## 3 Results  
### Characteristics of Coastline Changes  
#### 3.1.1 Variation of Coastline Length  
According to the seven remote sensing images of the study area from 1990 to 2018, the total length of the coastline in each period was obtained by visual interpretation (Figure 4). In order to ensure the accuracy of the extracted coastline data, GF-2 images with a resolution of 4 m were used in this study. The results of coastline extraction were verified by UAV photography, and the accuracy of coastline extraction was calculated. The results showed that the typing accuracy of the coastline extracted in this study reached 97.02% and the length accuracy of the coastline reached 94.78%. In the chart, it is clear that 2015 is a time node for the change of coastline length. Before 2015, the port areas headed by Penglai, Longkou, and Zhifu developed rapidly. The coastline length showed a continuous growth trend, that is, it increased by 174.15 km, an increase of 41.53%. In 2015, the relevant departments began to take effective measures to repair the islands and coastlines in view of the excessive exploitation and utilization of the ocean and coastal zones and the impact of natural disasters, such as typhoons and \begin{table}
\begin{tabular}{c c} \hline \hline
**The First Type** & **Classification Definition** \\ \hline Cultivated land & Land reclaimed, cultivated and managed regularly. \\ Forests/gresses cover & It mainly includes mangroves, other woodlands, and grasslands. \\ Building areas & Including housing construction area, independent housing construction \\  & and abandoned housing construction. \\ Roads & It includes railways, highways, urban roads, and rural roads. \\  & An engineering entity or ancillary building facility built for a purpose of \\ Structures & use, in which production and living activities are not carried out directly \\  & within it(GB/T 50504-2009). Including hardened surface, industrial \\  & facilities, salt ponds, dykes, and other structures. \\ Manually excavated land & Ground surface covered by human waste or exposed by human \\  & excavation for a long time. \\ Desert/bare land & Desert and bare surface and low coverage grassland. \\  & It refers to the spatial range of the water body’s growth and declines \\  & over a long period of time. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Classification system of coastal surface cover in Yantai. Figure 3: Different images taken by an unmanned aerial vehicle (UAV). ocean storm surges [32]. The length of the coastline showed a relatively stable small growth trend with a cumulative increase of 6.93 km, an increase of approximately 1.16% in 2015. According to the trend map of coastline length change in the study area from 1990 to 2018, the coastlines of several periods were selected randomly to calculate the intensity of coastline change (Table 3). In the past 30 years, the changing intensity of coastline length in the study area is approximately 1.54%. The changing intensity of coastline length in the study area was the greatest during 2010-2015 with a value of 3.47%. The changing intensity of coastline length in the study area was the smallest during 2015-2018 with a value of 0.39%. Figure 5 shows the coastline type and length information in different years of the counties and municipalities in the study area. From 1990 to 2018, the natural, artificial, and estuarine boundary lines in the northern part of Yantai changed significantly. The length of natural boundary lines decreased rapidly from 315.42 km to 202.79 km, then slowly decreased to 201.13 km. On the contrary, the length of the artificial boundary line increased rapidly at first and then increased slowly. Its size increased from 101.94 km in 1990 to 396.47 km in 2018. The length of the estuary boundary line increased, but the overall change is not significant. From 1990 to 2015, the length of the artificial boundary line in the study area continued to increase.