River mask before and after the Elwha dam removals, WA.

Two dams located on the Elwha River in Washington state were removed from 2011 to 2014. This resource contains a river mask prior to the removal in 2011 and three subsequent mask files from 2013, 2015, and 2017 showing the morphological evolution of the channel. The output river mask raster data were created using publicly available aerial imagery from the National Agricultural Imagery Program. First, supervised classification was performed to classify all water, non-water (vegetation, bare soil, and urban), water shadow, and non-water shadow pixels. The clear water and shadow water pixels were then reclassified as one, and finally, pixels around bridge cross sections, and additional misclassified pixels were manually corrected for each time period.

位于华盛顿州埃尔瓦河（Elwha River）上的两座大坝于2011年至2014年间被拆除。本数据集包含2011年大坝拆除前的河流掩膜（river mask）数据，以及2013、2015和2017年的三期后续掩膜文件，用于展示河道的形态演变过程。本次产出的河流掩膜栅格数据（raster data），依托美国国家农业影像项目（National Agricultural Imagery Program）的公开航空影像制作生成。首先通过监督分类（supervised classification）对所有像素进行类别划分，涵盖水体、非水体（植被、裸土与城镇用地）、水体阴影及非水体阴影四类像素。随后将清澈水体与阴影覆盖下的水体像素合并为同一类别；最后针对各时期的数据集，对桥梁断面周边像素及其他额外误分类像素进行人工修正。