Landsat长时间序列的阳澄湖湖面围网时空变化

Abstract

准确提取湖泊围网区域的时空分布信息对湖泊的保护和可持续发展具有重要意义。本文以阳澄湖为研究区域，收集该地区1984年—2017年所有的Landsat 5和Landsat 8影像（共计396景），提出了结合光谱和纹理特征的围网提取新算法，同时利用时间序列滤波消除年际间因数据不一致造成的偏差。以高清影像人工解译作为参考，阳澄湖围网提取结果的生产者精度在72.57%—88.53%，用户者精度在79.79%—98.10%，围网面积变化与文献记录吻合。结果表明，阳澄湖围网经历了“无围网期”（1984年—1994年）、“快速增长期”（1994年—1998年）、“巅峰期”（1999年—2002年）、“快速下降期”（2003年—2006年）和“稳定期”（2007年—2017年）5个阶段，最高达到100 km2，目前稳定在30 km2；通过研究围网区植被指数发现，2002年之后围网区浮水植物的种植面积增大；通过对比水质数据发现，2002年至今持续15年的围网拆除并未使阳澄湖恢复到80年代无围网养殖时期的Ⅱ类水，其水质依然处于Ⅲ—Ⅳ类。因此在湖泊养殖开发过程中，政府应该坚持可持续发展道路，在不破坏湖泊水质的基础上发展湖泊经济。

Accurate extraction of temporal-spatial information of the enclosure culture area is important to the protection and sustainable development of a lake. In this study, we presented a new method to extract enclosure culture area with long-term Landsat time series. First, we collected all the available Landsat 5 and 8 scenes over Yangcheng Lake from 1984 to 2017 (a total number of scenes of 396). Then, a new algorithm using spectral and texture information was proposed to extract the enclosure culture area. Furthermore, a temporal filter was designed to smooth the time-series results for eliminating the deviation caused by data inconsistency between years. Finally, the manually determined enclosure culture area based on the Google Earth high-resolution image was used as the ground truth reference. Results showed that the producer's accuracies of the final results were between 72.57% and 88.53%, whereas the user's accuracies were between 79.79% and 98.10% for three selected years (i.e., 2002, 2010, and 2015). The enclosure culture area in Yangcheng Lake had experienced five stages: no-enclosure culture (1984-1994), rapidly growing (1994-1998), peak (1999-2002), rapidly declining (2003-2006), and stability (2007-2017), with the largest area up to 100 km2 and the current area maintained to 30 km2. By studying the vegetation index (normalized difference vegetation index in this study) of the enclosure culture area, we found that the amount of float vegetation grown significantly after 2002. Comparison with the water quality data showed that the water quality of Yangcheng Lake had not improved significantly since it reached IV level in 2003, although the enclosure culture area had been decreasing since 2002. Therefore, in the development of lake culture, the government should insist on sustainable development and develop the lake economy while maintaining the lake water quality. © 2019, Science Press. All right reserved.