首页 >  2022, Vol. 26, Issue (2) : 358-372

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DOI:

10.11834/jrs.20211287

收稿日期:

2021-05-12

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Sentinel时序影像的长江流域地表水体提取
刘宇晨1,2,高永年3
1.中国科学院南京地理与湖泊研究所 流域地理学重点实验室, 南京 210008;2.中国科学院大学, 北京 100049;3.河海大学 地球科学与工程学院, 南京 211100
摘要:

传统水体提取算法大多基于某一时期单景遥感影像,无法表现出水体随着时间和空间高度可变的特性,虽然国内外已出现部分时序水体数据产品,但其空间分辨率及水体边界的精度仍无法满足一些研究和应用的需要。本文以地表环境复杂的长江流域为研究区,基于GEE(Google Earth Engine)云平台,使用Sentinel-2 MSI年内长时序影像集结合像元的“时间特征”,提出一种在大尺度环境下更具普适性、可操作性且效果更好的高精度水体提取算法,即基于时序影像数据结合多指数和“时间特征”并融合DEM的算法。该算法选择自动提取水体指数(AWEI)、改进型归一化差值水体指数(MNDWI)、归一化植被指数(NDVI)和增强型植被指数(EVI)进行多指数逻辑组合来提取水体;同时利用NIR波段反射率值和SRTM数字高程模型生成的坡度数据集来辅助抑制高反射率噪声和阴影噪声。通过目视解译采取验证样本点进行全流域水体精度验证,正确提取率达96%以上;在亚像元层面进行精度评估,混合边缘像元占像元总数的3.37%,错分误差0.46%,漏分误差0.21%,表明本文算法对混合像元具有较好的抑制效果;对比传统基于光谱特征的NDWI、MNDWI水体指数,多指数结合时间特征的算法在抑制阴影噪声方面效果更佳;对比现有部分水体数据产品,本文算法在一定程度上既能保证水体区域整体的完整性,也保留了水体的局部细节,在细小水体的提取上具有一定优势。由长江流域水体遥感提取结果可得,流域内水体空间分布不匀,且各水体类型时空变化特征明显,2017年—2020年永久性水体增加的67.41%是由季节性水体转化而来,季节性水体与非水体之间的相互转化最为显著,季节性水体增加的74.64%是由非水体转化而来,同时季节性水体减少的56.25%转化为了非水体。实验结果表明:本研究算法在提取不同时空位置和不同环境下的水体具有一定的普适意义,可有效避免水体与其他地物混合造成的“同物异谱”和“同谱异物”现象,同时对复杂背景噪声有着良好的抑制作用,具有较高的准确度和精度。

Surface water extraction in Yangtze River Basin based on sentinel time series image
Abstract:

Traditional water extraction algorithms are mostly based on single-scene remote sensing image of a certain period and cannot show the highly variable characteristics of water bodies over time and space. Although some time series water products have appeared in China and abroad, their spatial resolution and water boundary accuracy still cannot meet the needs of some studies and applications. This paper takes the Yangtze River Basin with complex surface environment as the research area based on the Google Earth Engine (GEE) cloud platform. The Sentinel-2 MSI annual long time series image sets are combined with the “temporal characteristics” of pixels, and a high-precision water extraction algorithm with more universality, operability, and better effect in large-scale environment is proposed. Specifically, an algorithm based on time series image data is combined with multi-index and “temporal characteristic” fusion Digital Elevation Model (DEM). This algorithm selects automated water extraction index, Modified Normalized Difference Water Index (MNDWI), normalized difference vegetation index, and enhanced vegetation index for multi-index logical combination to extract water bodies. Near-infrared band reflectivity value and slope data set generated by SRTM DEM are used to assist in suppressing high reflectivity noise and shadow noise. The accuracy of water bodies in the whole basin is verified with the validation sample points, and the correct extraction rate is more than 96% through visual interpretation. The accuracy evaluation at the subpixel level shows that the mixed edge pixels account for 3.37% of the total pixels, the misclassification error is 0.46%, and the omission error is 0.21%, indicating that the proposed algorithm has a good inhibitory effect on the mixed pixels. Compared with the traditional NDWI and MNDWI water index based on spectral characteristics, the multi-index combined with temporal characteristic algorithm has better effect in suppressing shadow noise. Compared with some existing water products, the proposed algorithm can ensure the integrity of the whole water area and retain the local details of the water body. It has certain advantages in the extraction of small water bodies. Results of the remote sensing extraction of water bodies in the Yangtze River Basin show that the spatial distribution of water bodies in the basin is uneven, and the temporal and spatial changes in various water body types are obvious. From 2017 to 2020, 67.41% of the increase in permanent water bodies is transformed from seasonal water bodies, and the mutual conversion between seasonal water bodies and nonwater bodies is the most obvious. In addition, 74.64% of the increase in seasonal water bodies is converted from nonwater bodies, and 56.25% of the decrease in seasonal water bodies is converted to nonwater bodies. Experimental results show that the proposed algorithm has a certain universal importance in extracting water bodies in different spatiotemporal locations and different environments and can effectively avoid the phenomenon of “the same objects with different spectra” and “the same spectra with different objects” caused by the mixing of water and other ground objects. This algorithm has a good inhibitory effect on complex background noise and has high accuracy and precision.

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