Maine_Elevation_DEM_Statewide

This is a tiled collection of 1-meter resolution elevation data developed under the 2025 Maine GeoLibrary Seamless Elevation project and sourced from the USGS 3D Elevation Program (3DEP). The 3DEP data holdings serve as the elevation layer of The National Map and provide foundational elevation information for earth science studies and mapping applications in the United States. 3DEP data are used for hydrologic modeling, resource monitoring, mapping and visualization, and many other applications. The elevations in this DEM represent the topographic bare-earth surface. USGS standard one-meter DEMs are produced exclusively from high resolution light detection and ranging (LiDAR) source data of one-meter or higher resolution. One-meter 3DEP DEM surfaces are seamless within individual collection projects, but not across projects. Substantial differences in measured elevation values often occur along the boundaries of different collections. The largest of these differences are presumably caused by changes in bare-earth elevation occurring between LiDAR collections. Lesser differences may have other causes, including changes in vegetative cover. Under the 2025 Maine GeoLibrary Seamless Elevation project, DEM data were processed to eliminate or mitigate discrepancies between adjacent 3DEP collections, yielding a seamless and complete coverage for the state of Maine. Statewide coverage was provided by 3DEP LiDAR projects executed from 2016 through 2023. Areas of overlap were identified between all collections, and boundaries, or cutlines, between collections were established using an algorithm that searches for optimal cutlines by minimizing the sum of differences between DEM values along the length of candidate cutlines. The search for optimal cutlines was further constrained to avoid water bodies whenever possible due to differences in water body elevation between LiDAR collections. When stitching together elevation data from adjacent collections, differences along the cutline were further mitigated by feathering elevation values within 10 meters to either side of the cutline (elevation values within 10 meters of a cutline were computed as weighted averages of the overlapping DEMs, with weights determined by distance from the cutline). Seamless processing altered 3DEP elevation values only within 10 meters of defined cutlines. Outside of these areas, elevation values in this seamless dataset match the original 1-meter 3DEP data.The spatial reference used for tiles of this 1-meter seamless DEM data is Universal Transverse Mercator (UTM), zone 19N, in units of meters, and in conformance with the North American Datum of 1983 (NAD83). Bare earth elevation values are in meters and are referenced to the North American Vertical Datum of 1988 (NAVD88). The public distribution of certain high-resolution 3DEP products and their derivatives is restricted for Penobscot Nation Tribal lands. The Penobscot Nation shared access to restricted 3DEP elevation data for seamless processing, but Tribal lands were subsequently removed from seamless output prior to public release.本数据集为2025年缅因州地理库无缝高程项目开发的1米分辨率高程分幅瓦片数据集，数据源自美国地质调查局（USGS）3D高程计划（3D Elevation Program, 3DEP）。3DEP数据馆藏作为《国家地图集》（The National Map）的高程图层，为美国的地球科学研究与制图应用提供基础高程信息。3DEP数据可用于水文建模、资源监测、制图与可视化等诸多场景。本数字高程模型（Digital Elevation Model, DEM）中的高程值代表地形裸地表层。美国地质调查局标准1米分辨率DEM仅由分辨率不低于1米的高分辨率激光雷达（Light Detection and Ranging, LiDAR）源数据生成。1米分辨率3DEP DEM数据在单个采集项目内部可实现无缝拼接，但跨项目间无法保证无缝性。不同采集项目的边界处往往存在显著的高程测量值差异，这类差异的主要成因推测为激光雷达采集时段内裸地高程的变化，次要成因则可能包括植被覆盖的改变。在2025年缅因州地理库无缝高程项目框架下，研发人员对DEM数据进行处理，以消除或缓解相邻3DEP采集项目间的高程差异，最终实现缅因州全域的无缝完整覆盖。本次全域覆盖所用的3DEP激光雷达采集项目均完成于2016年至2023年间。研究人员识别了所有采集项目间的重叠区域，并通过算法确定各项目间的边界或割线：该算法通过最小化候选割线沿线DEM数值差值的总和，寻找最优割线。由于不同激光雷达采集项目间水体高程存在差异，最优割线的搜索过程会额外约束，尽可能避开水体区域。在拼接相邻采集项目的高程数据时，研发人员还通过对割线两侧10米范围内的高程值进行羽化处理，进一步缓解割线沿线的高程差异：割线两侧10米范围内的高程值由重叠DEM数据加权平均计算得到，权重由该点到割线的距离决定。无缝处理仅会改变划定割线10米范围内的3DEP原始高程值，在此区域之外，本无缝数据集的高程值与原始1米分辨率3DEP数据完全一致。本1米分辨率无缝DEM数据瓦片采用的空间参考为通用横轴墨卡托（Universal Transverse Mercator, UTM）19N分带，单位为米，符合1983年北美大地基准（North American Datum of 1983, NAD83）规范。裸地高程值以米为单位，基准为1988年北美垂直基准（North American Vertical Datum of 1988, NAVD88）。部分高分辨率3DEP产品及其衍生数据的公开分发，在彭诺布斯科特族部落领地范围内受到限制。彭诺布斯科特族曾授权使用受限的3DEP高程数据用于无缝处理，但在最终公开发布前，部落领地范围已从无缝输出结果中移除。