Maine Orthoimagery Regional SPOT 2004 (Imagery Layer)

These data are panchromatic satellite data from the French SPOT-5 satellite. They represent a black-and-white "picture" of Earth from the satellite using 5-meter pixels (5m x 5m squares) as the minimum unit for imaging. The collection dates are mostly during the leaf-on season in 2004. Two scenes are from winter collects and snow/ice can be seen. This dataset was created through orthorectification of SPOT imagery using USGS Digital Orthophoto Quadrangles and Maine DEMs in ERDAS OrthoBASE 8.7. The orthorectified imagery was then warped using Space Imaging's proprietary Autowarp software. Autowarp computes tie points between two images based on correlation between similar points in the images and then applies a locally varying warp based on the tiepoints. The program was given an initial set of ground control points to create a coarse quadratic warp which was then refined through the addition of more points selected by the program. This work was done by Space Imaging and Sanborn staff. Certain high-elevation areas were further orthorectified by i-cubed to reduce horizontal error. Color balancing for the mosaic was done using GIMP image processing software by Maine DEP GIS staff. Note that balancing was done to enhance vegetated areas. In most cases, this means loss of contrast in urban areas. The raw data are much darker, but would provide more detail in urban areas than these processed data (at the expense of loss of contrast in vegetated areas). These data are part of the MELCD 2004 landcover and impervious mapping project for Maine. The data are LICENSED to the following entities: -Federal Government organizations when working with Maine on joint projects -All State Government departments and agencies within Maine -Regional county and local governments within Maine -K-12 schools, State Colleges and Universities within Maine. These data were the base imagery for the MELCD 2004 project. They were merged with LandSat TM data to create sharpened multispectral data for landcover mapping.本数据集为法国SPOT-5卫星获取的全色（panchromatic）卫星影像数据，以5米像素（5m×5m正方形单元）作为成像最小单位，呈现了卫星拍摄的地球黑白影像。数据采集日期大多集中于2004年的植被展叶季，另有两景影像采集于冬季，可观测到积雪或冰面。 本数据集通过对SPOT影像进行正射校正（orthorectification）处理得到，处理过程中采用了美国地质调查局（USGS）数字正射影像图幅与缅因州数字高程模型（DEM），并使用ERDAS OrthoBASE 8.7软件完成操作。经正射校正的影像随后通过太空成像公司（Space Imaging）的专有Autowarp软件进行了局部几何形变校正。Autowarp软件通过影像间相似点的相关性计算两景影像间的同名控制点（tie points），随后基于这些控制点执行局部自适应的几何形变校正。该软件首先通过初始地面控制点（ground control points，GCP）集生成粗略的二次多项式形变校正结果，随后通过软件自动选取的新增控制点对校正结果进行精细化优化。 此项处理工作由太空成像公司与Sanborn公司的工作人员完成。部分高海拔区域由i-cubed公司进一步开展正射校正，以降低水平定位误差。 镶嵌影像的色彩平衡处理由缅因州环境保护局（Maine DEP）地理信息系统（GIS）工作人员使用GIMP图像处理软件完成。需注意，本次色彩平衡旨在增强植被区域的视觉效果，多数情况下会导致城区区域的对比度下降。原始影像整体偏暗，但相较于本处理后的影像，其能在城区呈现更多细节，代价是植被区域的对比度会有所损失。 本数据集属于缅因州2004年MELCD土地覆盖与不透水面制图项目的一部分。本数据集的授权使用对象包括以下主体： - 与缅因州开展联合项目的联邦政府机构 - 缅因州内所有州政府部门及机构 - 缅因州内的区域县级及地方政府 - 缅因州内的K-12学校、州立学院及大学 本数据集为MELCD 2004项目的基础影像数据，研究人员将其与LandSat TM影像数据融合，生成用于土地覆盖制图的增强型多光谱影像。