全球多尺度海岸线数据在珠江口岸线的精度评价及适用性分析

以珠江口为研究区，对全球自洽分层高分辨率地理数据库（GSHHG）中的全分辨率、高分辨率、中分辨率、低分辨率和粗分辨率等5种海岸线数据开展评价与适用性分析，评估5个尺度海岸线数据的长度及其分形维数差异，并选择珠江口两岸部分区域为例，以不同时期陆地资源卫星Landsat影像为基础，对比不同尺度GSHHG海岸线数据与实际数据之间的差异。结果表明：1）5个尺度海岸线数据的长度及分形维数具有显著差异，分辨率越高，岸线长度越长，其分形维数也越大；2）通过与1978和2018年2个时期基于Landsat影像提取的岸线数据对比表明：GSHHG海岸线数据与实际数据在岸线长度及形态特征上总体一致，但GSHHG海岸线的形态特征与1978年海岸线更接近，反映的是较为早期的海岸线特征。最后建议在进行海岸线变迁与现状调查时，需要根据海岸线长度、岸线形态复杂程度等谨慎选择海岸线数据。

Assessment of Precision and Usability of a Global Multi-Scale Coastline Dataset Using the Pearl River Estuary as a Test Model

The Global, Self-consistent, Hierarchical, High-resolution Geography (GSHHG) Database, provided by the National Centers for Environmental Information and widely used worldwide, includes global multi-scale coastline data. Although many scientists have utilized this database in their studies, the database itself has not been thoroughly evaluated. The different scales available through the GSHHG database include full resolution, high resolution, intermediate resolution, low resolution, and crude resolution. The Pearl River estuary was selected as our study site. These studies involve the use of the GSHHG database, Landsat MSS from 1978, and Landsat OLI from 2018 to evaluate the differences in coastline length and fractal dimensions among GSHHG datasets collected at five different resolution levels. This study also selected eastern and western sub-regions to compare differences between coastline maps from the GSHHG and Landsat datasets. In addition, the coastline extracted from resampled Landsat OLI data from 2018 (80 m), covering the eastern part of the Pearl River Estuary was compared with the same coastline data extracted from Landsat OLI at 30 m spatial resolution. Coastline lengths according to full resolution, high resolution, intermediate resolution, low resolution, and crude resolution data are 1509.47 km, 1398.12 km, 1212.54 km, 692.00 km, and 326.40 km, respectively. The corresponding fractal dimensions from the GSHHG database were 1.2983, 1.2832, 1.2588, 1.0990, and 1.0262 for full resolution, high resolution, intermediate resolution, low resolution, and crude resolution, respectively. Separate eastern and western segments of the Pearl River Estuary demonstrate that for a given area, full resolution of GSHHG data provides the longest and most detailed rich coastline data relative to the coastline data extracted from the Landsat data and GSHHG database. The length of the coastline extracted from the 1978 Landsat MSS was most similar to the length obtained from high-resolution GSHHG. The data on the morphology of the coastline in the 1978 Landsat MSS were much closer to the full resolution, high resolution, and intermediate resolution data obtained from GSHHG. Compared to the coastline data extracted from 80 m Landsat OLI and 30 m Landsat OLI, a 17.68% length difference was found. Fractal dimension differences were 1.7%. The results show that: (1) The length and fractal dimensions of coastline data produced at five different resolutions are substantially different. Higher-resolution data produce longer coastline lengths and more complex coastline morphologies; (2) Using coastline data extracted from Landsat data in 1978 and 2018 as references, GSHHG coastline dataset was found to be generally consistent with real data shoreline length and morphological characteristics. The morphological characteristics of the GSHHG coastline are closer to the real data from 1978, which does not reflect the current situation of the Pearl River Estuary. The GSHHG database only includes one phase of data, implying that scientists cannot accomplish studies related to coastline change without using additional data. Nevertheless, studies on comparisons between different regions of coastline could select data based on the characteristics of a study area. It is suggested that scientists select coastline data based on coastline length, complexity, and morphology when studying coastline changes in response to situations of interest.