1975 UMRS Land Cover/Land Use -- Open River 2

The Great River Environmental Action Team (GREAT) was a federal/state multi-agency cooperative program established in the late 1970's to evaluate current resource management practices and develop management strategies for the Upper Mississippi River (UMR). One of the problems facing the GREAT project was the lack of available information on many of the river's components. One project implemented by GREAT was the creation of a land cover/land use (LCU) database derived from color infrared aerial photography collected in 1975. Mississippi River Pools 3 through 10 were photographed at a scale of 1:9,600, and Lock and Dam 10 to the Ohio River were photographed at a scale of 1:24,000. The program's photo interpreters delineated whatever features could be viewed on the photos, using a minimum mapping unit that was less than half an acre. A contractor was hired to transfer the photo overlays for Pools 3 through 14 onto 1:24,000-scale USGS quadrangles, then automate the data using the geographic information system (GIS) program PIOS. The data were also distributed as map books that contained 1:6,000-scale enlargements of the photos and their overlays. During the data transfer process; the contractor hired to automate the data generalized it to a 2.5 acre minimum mapping unit. Documentation archived by the GREAT project described this automation process as; some polygons smaller than 2.5 acres and linear features were incorporated into nearby polygons. Others were manually enlarged so that the data contained within would be preserved. All generalizations were made in accordance with the guidelines established for the GREAT projects. The digital data sets were then enhanced by the GREAT project. Unfortunately no record of the enhancements or an archive of the original digital dataset are known to exist. The enhanced digital data, copies of the aerial photo overlays, copies of most of the map books, and some of the photos themselves were archived and preserved by the various agencies that participated in the GREAT project. These data were then passed to the Upper Midwest Environmental Sciences Center (UMESC) in the late 1980's and 1990's when the center became the administrator for the Upper Mississippi River System's Long Term Resource Monitoring Program (LTRMP). Comparisons of the archived digital data set to the photos and their overlays displayed discrepancies that were difficult to document. The 1975 data set is viewed by many as an important baseline data set, so in 1999 UMESC decided to use the archived photo overlays to (1) address the data discrepancies by reautomating Pools 3 through 14, and (2) complete the data set by automating Lock and Dam 14 to the Ohio River.大河环境行动小组（Great River Environmental Action Team，GREAT）是一项于20世纪70年代末设立的联邦/州级多机构合作项目，旨在评估密西西比河上游（Upper Mississippi River，UMR）现行的资源管理实践并制定相应管理策略。GREAT项目面临的核心挑战之一，是该河流诸多组成部分缺乏可用的相关信息。该项目实施的一项重要工作，是基于1975年采集的彩色红外航空摄影影像，构建土地覆盖/土地利用（land cover/land use，LCU）数据库。其中，密西西比河第3至10号航道段的摄影比例尺为1:9600，而从10号船闸大坝至俄亥俄河的区域摄影比例尺为1:24000。项目的影像解译人员对影像上可识别的所有地物进行勾绘，采用的最小制图单元小于0.5英亩。项目方聘请承包商将第3至14号航道段的影像叠加图层转绘至比例尺为1:24000的美国地质调查局（United States Geological Survey，USGS）标准图幅中，随后通过地理信息系统（Geographic Information System，GIS）软件PIOS实现数据自动化处理。该数据集还以地图册形式分发，其中包含比例尺为1:6000的航空影像及其叠加图层的放大图。在数据转绘过程中，负责数据自动化处理的承包商将最小制图单元统一调整为2.5英亩，对数据进行了概化处理。GREAT项目归档的文档对该自动化处理过程描述如下：将面积小于2.5英亩的面要素与线性要素并入邻近的面要素，部分要素则通过手动放大以保留其内部包含的属性数据。所有概化处理均严格遵循GREAT项目制定的相关规范。随后GREAT项目对该数字数据集进行了增强处理，遗憾的是，目前未发现该增强处理的相关记录，也无原始数字数据集的归档副本。经增强处理的数字数据、航空影像叠加图层副本、大部分地图册副本以及部分原始航空影像，由参与GREAT项目的各合作机构进行了归档保存。上述数据于20世纪80年代末至90年代被移交至中北部环境科学中心（Upper Midwest Environmental Sciences Center，UMESC），该中心彼时已成为密西西比河上游系统长期资源监测项目（Long Term Resource Monitoring Program，LTRMP）的管理方。将归档的数字数据集与原始航空影像及其叠加图层进行比对后，研究人员发现了难以溯源的数据偏差。诸多研究者将1975年的数据集视为重要的基准数据集，因此UMESC于1999年决定利用归档的影像叠加图层开展两项工作：一是对第3至14号航道段重新进行自动化处理以修正现存的数据偏差，二是对14号船闸大坝至俄亥俄河的区域开展自动化处理以完善整套数据集。