Sand classifications along the Colorado River in Grand Canyon derived from 2002, 2009, and 2013 high-resolution multispectral airborne imagery

These data are remote sensing image-based classification maps of unvegetated river-derived sand along the Colorado River. One map is based on imagery acquired in May 2013 and is a classification of sand located above the wetted river channel in the imagery which was acquired at the approximate contemporary low-flow river discharge of 8,000 cubic feet per second (227 cubic meters per second) and extends from Glen Canyon Dam at Lake Powell to Separation Canyon at Lake Mead, a total distance of approximately 255 river miles (410 river kilometer). Three other maps are based on imagery acquired in May 2002, 2009, and 2013, respectively, and are classifications of sand located above the wetted river channel (at river discharge of approximately 8,000 cubic feet per second, or 227 cubic meters per second) and below the approximate maximum contemporary flood stage of the river at a discharge of 45,000 cubic feet per second (1,274 cubic meters per second). Those three maps extend from Lees Ferry (approximately 15 miles downstream of Glen Canyon Dam) to Diamond Creek, a total distance of approximately 226 river miles (364 river kilometers). These three maps only have sand classified within large sand deposition zones (SDZs) in the river corridor. Sand transported by the Colorado River through Grand Canyon is stored on the river bed and in recirculation zones, or eddies, that typically house separation or reattachment sandbars in the lee of debris fans (Schmidt, 1990; Hazel et al., 2006). Alternatively, sand can also be found lining pools and channel margins upstream of debris fans (Schmidt, 1990). The SDZs were identified by delineating individual large eddies and adjacent debris fans, pools and channel margins which contain a majority of the areas of exposed unvegetated river-derived sand that can be classified by multispectral image analysis. The more comprehensive 2013 sand map extends outside of the SDZs and encompasses all river-derived sand within the entire width and length of the river corridor above the low-flow river stage. Each classification map was derived from a combination of unsupervised and supervised image classification methods followed by exhaustive image interpretation and map editing to identify river-derived sand that was not vegetated and not obviously colonized by biologic soil crust. The sand classifications have the same 0.2-meter ground resolution as the imagery. No formal accuracy assessment has been completed at this time for these data.

本数据集为基于遥感影像生成的科罗拉多河沿岸无植被河道源沙分类图。其中一幅分类图基于2013年5月获取的影像，针对该影像中过水河道上方的沙体进行分类，影像获取时的河道流量近似当前枯水流量，为8000立方英尺每秒（227立方米每秒），覆盖范围从鲍威尔湖处的格兰峡谷大坝（Glen Canyon Dam）延伸至米德湖处的分离峡谷，河道总长约255河道英里（410河道公里）。另外三幅分类图分别基于2002年、2009年及2013年5月获取的影像，针对过水河道上方（对应河道流量约8000立方英尺每秒，即227立方米每秒）且低于当前河道近似最大洪水水位（流量为45000立方英尺每秒，即1274立方米每秒）区间内的沙体进行分类；这三幅图的覆盖范围从利斯渡口（Lees Ferry，即格兰峡谷大坝下游约15英里处）延伸至钻石溪，河道总长约226河道英里（364河道公里），且仅对河道廊道内大型沙沉积区（Large Sand Deposition Zones, SDZs）内的沙体完成分类。经科罗拉多河输运并流经科罗拉多大峡谷的沙体，会沉积于河床及回流区（或称涡流区）中，这些区域通常在碎屑扇背风侧发育分离沙洲或贴附沙洲（Schmidt, 1990; Hazel et al., 2006）；此外，沙体还可分布于碎屑扇上游的水塘及河道岸线区域（Schmidt, 1990）。大型沙沉积区（SDZs）通过勾绘划定单个大型涡流及相邻的碎屑扇、水塘与河道岸线来识别，这些区域涵盖了大部分可通过多光谱影像分析完成分类的裸露无植被河道源沙区域。覆盖范围更广的2013年沙体分类图突破了SDZs的范围，涵盖了枯水水位以上河道廊道全宽及全长内的所有河道源沙。每一幅分类图均通过结合非监督与监督影像分类方法，辅以详尽的影像解译与图件编辑，以识别未被植被覆盖且未明显被生物土壤结皮定植的河道源沙。该沙体分类结果与原始影像保持一致的0.2米地面分辨率。目前尚未针对本数据集开展正式的精度评估工作。