Coastline Extraction And Changes Analysis In Tianjin Binhai New Area Based On Landsat Image

The coastal zone is in the position at the junction of land and sea,with abundant natural resources.Due to the influence of human exploitation,the coastal zone changes constantly.Since 2006,The government implemented the 15th five-year plan for economic and social development of Tianjin Binhai New District,the coastline has changed rapidly and the scale of land reclamation has gradually expanded,which has a huge impact on the stability of the coastal ecosystem and the sustainable development of resources.Therefore,it is significant to adopt appropriate methods to dynamically monitor coastlines and reclamation areas.Land observation satellite has the characteristics of high time resolution,high space resolution and wide observation range.It can make up for the disadvantage of traditional surveying which is limited by region and the low timeliness of aerial photogrammetry pictures,and is widely used in coastal line extraction.Although there are many methods for automatically extracting coastlines using remote sensing images,the extraction effects of different coastlines are quite different.Due to the small spectral difference between water and silt in the image,the extraction effect of silt shoreline based on pixel single threshold is poor,and the degree of automation is low.Based on Landsat images,this paper extracted the coastline of Binhai New Area in Tianjin by utilizing NDWI,pixel area and spatial relationship characteristics,combined with membership function.Based on a certain number of checkpoints along the coastline,the extraction accuracy of a scene image were compared with the two means,edge detection and density segmentation based on NDWI.Furthermore,the method of multi-feature extraction combined with membership function was used to obtain the shoreline of Tianjin Binhai New Area in five periods from 2003 to 2020,and the accuracy of extracting shoreline on the five periods was evaluated.Finally,the paper analyzed the changes of the coastline and the reclamation of Binhai New Area and the internal mechanism and causes of the reclamation situation.The following results show that:(1)The method of multi-feature extraction combined with membership function can achieve high extraction accuracy for the coastline in different periods in the study area.In the five stages of images,the extraction accuracy of checkpoints on artificial shoreline is all higher than 85%and the highest is 92.3%;the extraction accuracy of checkpoints on silt shoreline is all higher than 71.4%and the highest is 87%,and the average extraction accuracy of five stages of images is 84.9%.(2)Compared with the other two methods of edge detection and density segmentation based on NDWI,the means of multi-feature extraction combined with membership function improves the accuracy of coastline extraction.The extraction accuracy of Canny operator on silt shoreline is higher than that of the density segmentation based on NDWI,and it is close to the extraction accuracy of artificial shoreline.Through the accuracy analysis of the extraction results of the coastline in the study area in 2013,the accuracy of the method of multi-feature extraction combined with the membership function to extract the artificial coastline and the silt coastline is 92%and 80%,the total extraction accuracy is 87.5%.The accuracy of the density segmentation methods based on NDWI is 78%and 46.7%,the total extraction accuracy is 80%.In edge detection,the accuracy of Canny operator is 88%and 66.7%,the total extraction accuracy is 66.3%.(3)By using multi-feature extraction combined with membership function,it is concluded that the coastline of Binhai New Area has changed significantly in recent20 years,and human influence is the dominant factor.From 2003 to 2020,the natural coastline decreased by 10.86km,nearly 72.7%,and the artificial coastline increased by 211.78km,nearly 1.5 times,with a total reclamation area of 329.29km~2.Since the implementation of marine development policy in Tianjin Binhai New Area in 2005,the increase of coastline and reclamation has been the largest.Therefore,effective monitoring and management of coastline has important guiding significance for the rational development of coastal areas.