Wickham J, Stehman S V, Neale A C, Mehaffey M
National Exposure Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, MD: 343-05, Research Triangle Park, NC 27711.
College of Environmental Science and Forestry, State University of New York, 322 Bray Hall, 1 Forestry Dr., Syracuse, NY 13210.
Int J Appl Earth Obs Geoinf. 2020 Feb;84:1-9. doi: 10.1016/j.jag.2019.101955.
The emergence of high-resolution land cover data has created the opportunity to assess the accuracy of impervious cover (IC) provided by the National Land Cover Database (NLCD). We assessed the accuracy of the 900 m NLCD2011 %IC for 18 metropolitan areas throughout the conterminous United States using reference data from 1 m land cover data developed as part of the United States Environmental Protection Agency's EnviroAtlas project. Agreement was assessed from two perspectives: 1) sensitivity to the size of the assessment unit used for the comparison, and 2) utility of NLCD %IC to serve as a proxy for high-resolution IC. The former perspective was considered because statistical relationships can be sensitive to assessment unit size and shape, and the latter perspective was considered because high resolution (reference) %IC data are not available nationwide. The utility of NLCD %IC as a proxy for the high resolution data was assessed for seven lattice (square) cell sizes ranging from 1 ha to 200 ha using four EnviroAtlas IC indicators: 1) %IC per 100 ha (1 km); 2) %IC by Census block group; 3) %IC within a 15 m (radius) of the riparian zone, and; 4) %IC within a 50 m (radius) of the riparian zone. Agreement was quantified as per assessment unit deviation (NLCD %IC - reference %IC) and summarized as Mean Absolute Deviation (MAD) and Mean Deviation (MD) both within and across the 18 metropolitan areas. Ordinary least squares (OLS) regression (y = reference %IC and x = NLCD %IC) was also used to evaluate the quality of the NLCD %IC data. MAD was ≤ 5% for six of the seven lattice cell sizes. MAD was also ≤ 5% for Census block groups > 100 ha and for both riparian units. These results suggest that uncertainty attributable to the measurement of %IC was no greater than the uncertainty related to the effect of IC on aquatic resources that have been derived from studies of aquatic condition (e.g., benthic fauna) over a range of %IC. Overall, agreement was variable from one metropolitan area to the next. Agreement improved as assessment unit size increased and declined as the level of urbanization (NLCD %IC) increased. NLCD %IC tended to underestimate reference %IC overall, but NLCD %IC was sometimes greater than reference %IC in urbanized settings.
高分辨率土地覆盖数据的出现为评估美国国家土地覆盖数据库（NLCD）提供的不透水覆盖（IC）的准确性创造了机会。我们使用作为美国环境保护局环境地图集项目一部分开发的1米土地覆盖数据中的参考数据，评估了美国本土18个大都市区900米NLCD2011不透水覆盖百分比（%IC）的准确性。从两个角度评估一致性：1）对用于比较的评估单元大小的敏感性，以及2）NLCD不透水覆盖百分比（%IC）作为高分辨率不透水覆盖（IC）代理的效用。考虑前一个角度是因为统计关系可能对评估单元的大小和形状敏感，考虑后一个角度是因为全国范围内没有高分辨率（参考）不透水覆盖百分比（%IC）数据。使用四个环境地图集不透水覆盖（IC）指标，针对从1公顷到200公顷的七个格网（正方形）单元大小，评估了NLCD不透水覆盖百分比（%IC）作为高分辨率数据代理的效用：1）每100公顷（1平方千米）的不透水覆盖百分比（%IC）；2）按人口普查街区组划分的不透水覆盖百分比（%IC）；3）河岸带15米（半径）范围内的不透水覆盖百分比（%IC），以及；4）河岸带50米（半径）范围内的不透水覆盖百分比（%IC）。一致性通过每个评估单元偏差（NLCD不透水覆盖百分比 - 参考不透水覆盖百分比）进行量化，并汇总为18个大都市区内部和之间的平均绝对偏差（MAD）和平均偏差（MD）。还使用普通最小二乘法（OLS）回归（y = 参考不透水覆盖百分比，x = NLCD不透水覆盖百分比）来评估NLCD不透水覆盖百分比（%IC）数据的质量。七个格网单元大小中的六个，平均绝对偏差（MAD）≤5%。对于面积大于100公顷的人口普查街区组以及两个河岸单元，平均绝对偏差（MAD）也≤5%。这些结果表明，归因于不透水覆盖百分比（%IC）测量的不确定性不大于与不透水覆盖（IC）对一系列不透水覆盖百分比（%IC）的水生资源影响（例如底栖动物）相关的不确定性。总体而言，不同大都市区之间的一致性各不相同。随着评估单元大小的增加，一致性提高；随着城市化水平（NLCD不透水覆盖百分比）的增加，一致性下降。总体而言，NLCD不透水覆盖百分比（%IC）往往低估参考不透水覆盖百分比（%IC），但在城市化环境中，NLCD不透水覆盖百分比（%IC）有时会大于参考不透水覆盖百分比（%IC）。
