基于遥感影像分析1989—2019年黄河内蒙古段河冰时空变化

获取河冰时空分布信息对黄河流域防凌减灾工作及沿岸地区可持续发展具有重要意义。收集黄河内蒙古段1989—2019年冬季河冰遥感影像数据；提出了归一化未封冻水体指数（NDUWI）用以剥离被归一化雪指数（NDSI）误分为河冰的水体像元，确定了该指数划分河冰、水体像元的阈值，并利用NDUWI结合NDSI的方法提取河冰信息进而分析河冰时空分布及变化特征，探讨了海勃湾水库调度及河床演变对河冰分布的影响。结果表明：黄河内蒙古段河冰主要分布在研究区中游（巴彦高勒—三湖河口）。1989年以来，研究区内河冰经历“平稳期”（1989—1997年）、“扩张期”（1998—2000年）、“萎缩期”（2001—2019年）3个阶段，其中2000年出现河冰面积峰值，并于2019年减小至最小。各子段中，海勃湾至巴彦高勒（R1段）2015年前河冰分布稳定，2015年起受海勃湾水库建成影响，河冰面积大幅萎缩；巴彦高勒至头道拐（R2~R4段）河冰面积变化特征大体与全段变化相同。空间上，2015年后R1段以纵向萎缩为主，巴彦高勒至三湖河口（R2段）左岸河冰萎缩，右岸河冰堆积仍有偎堤风险；三湖河口至包头（R3）段全段河冰漫滩现象严重，2016年起得以缓解；包头至头道拐（R4）段以局部漫滩为主，2016年开始以主槽封冻为主。上游海勃湾水库建成后的常规运用可有效减小下游黄河内蒙古段的河冰漫滩现象。研究成果可为黄河内蒙古段水库防凌调度及堤防安全隐患排查提供参考。

A satellite-based analysis on spatial-temporal distribution and variation of river ice in Inner Mongolia reach of the Yellow River from 1989 to 2019 based on remote sensing image interpretation

Accurate extraction of temporal-spatial information of the river ice is important to the ice prevention and sustainable development of Inner Mongolia section in Yellow River basin. Based on the remote sensing image data （93 scenes） of the winter river ice in the Inner Mongolia section of the Yellow River from 1989 to 2019， this study proposes Normalized Difference Unfrozen Water Index（NDUWI） to replace the single-band reflectance value of stripping water information in SNOMAP algorithm， and determines the threshold value of dividing river ice and water pixel. The information of river ice in the Inner Mongolia section of the Yellow River is extracted by the modified SNOMAP algorithm， and the spatial and temporal distribution and variation characteristics of river ice is analyzed. The results show that the middle reach of the study area （Bayangaole-Sanhu Estuary） is abounded with more river ice than the other reach. Since 1989， river ice of the study area sequentially underwent “stabilized phase” （1989—1997）， “expansion phase” （1998—2000）， and “shrinkage phase” （2001—2019）. Among all sub-sections， the distribution of river ice of R1 section prior to 2015 was stable； since 2015， the frozen section of the river has witnessed reduced in length； the area variations of river ice of the R2 section and R3 section are similar to that of the full section. The shrinkage rate of the left bank of R2 section is faster than that of its right bank， and the distribution of river ice of R3 section is primarily concentrated on its both banks. The significant fluctuation of river ice of R4 section is steadily decelerating with the passage of time. The distribution of river ice is mainly driven by the change of river regime. The research results can be used as reference for reservoir traffic control in the upper reaches of Inner Mongolia section of the Yellow River and the determination of potential risk dike sections.