High-Resolution Orthorectified Imagery from 1999, Resampled to 10 meter, Niwot Ridge LTER Green Lakes Valley Project Area, Colorado

Orthophoto has been resampled to 10 meter. The 1:12,000 photos were flown by Rocky Mountain Aerial, the LTER project manager is Don Cline.
The Green Lakes Valley orthophoto was produced using 8 black and white photograph stereopair diapositives, flown at 1:12,000 scale in September, 1994 by Rocky Mountain Aerial, Denver, Colorado. Two flightlines were used to create this orthophoto, as there was not enough information in one flightline to include the entire GLV watershed. The diapositives were scanned in using ASIs high resolution drum scanner. An evenly spaced 25-m cellsize DEM was created from dtm.xyz using the outer boundary of the photographs. This DEM was used to register the 1:12,000 stereopairs to the UTM coordinate system with a horizontal location accuracy of 25-m. Once the 1:12,000 photographs were registered and rectified a .5-m cellsize digital orthophoto was produced for the Green Lakes Valley. There were a few problems with orthophoto generation in this area, mostly because of the steep terrain. Firstly, the stereopairs were NOT flown to generate othophotos, they were flown to generate DEMs. Because of this there was not enough overlap for generation of a seamless orthophoto. As the photos were warped to fit a planimetric base, there were a few areas with no data in the middle of the orthophoto. These areas were minimized because of ASIs expertise, but they show up as small black bars in the middle of the orthophoto. There are also some layover problems because of the steep terrain. This is caused by a steep mountain on the edge of the photo that lays over in one direction on one photo and lays over in another direction on the photo beside it. NOTE: This EML metadata file does not contain important geospatial
data processing information. Before using any NWT LTER geospatial
data read the arcgis metadata XML file in either ISO or FGDC compliant
format, using ArcGIS software (ArcCatalog > description), or by
viewing the .xml file provided with the geospatial dataset.

正射影像（Orthophoto）已重采样至10米分辨率。本次使用的1:12000比例尺航片由Rocky Mountain Aerial公司航拍，长期生态研究（Long-Term Ecological Research, LTER）项目负责人为Don Cline。

绿湖谷（Green Lakes Valley）正射影像由8张黑白立体像对透明正片制作而成，该批航片于1994年9月由科罗拉多州丹佛市的Rocky Mountain Aerial公司以1:12000的比例尺航拍。由于单条航线无法覆盖完整的绿湖谷（GLV）流域，本次正射影像制作共使用了两条航拍航线。上述透明正片通过ASI高分辨率滚筒扫描仪完成数字化扫描。基于航片的外边界，从dtm.xyz文件中生成了格网间距均匀、像元尺寸为25米的数字高程模型（Digital Elevation Model, DEM）。利用该DEM将1:12000比例尺的立体像对配准至通用横轴墨卡托（Universal Transverse Mercator, UTM）坐标系，平面定位精度达25米。完成1:12000比例尺航片的配准与纠正后，即可为绿湖谷生成像元尺寸为0.5米的数字正射影像。

该区域的正射影像制作过程中存在若干问题，主要源于地形陡峭。其一，本次立体像对的航拍初衷并非用于制作正射影像，而是为了生成DEM。正因如此，像片重叠度不足，无法生成无缝正射影像。由于航片需经扭曲以适配平面基准，正射影像中部存在部分数据缺失区域。得益于ASI的专业技术，此类区域已被尽量缩减，但仍会在正射影像中部呈现为小型黑色条带。此外，受陡峭地形影响，还存在部分叠掩（layover）问题：该问题源于航片边缘的陡峭山体，在一张航片上山体沿某一方向发生叠掩，而在相邻航片上则沿另一方向出现叠掩。

注意：本生态元数据语言（Ecological Metadata Language, EML）文件未包含重要的地理空间数据处理信息。在使用任何NWT LTER地理空间数据前，请通过ArcGIS软件（ArcCatalog > 描述）查看符合ISO或FGDC格式的ArcGIS元数据XML文件，或直接查看随地理空间数据集一同提供的.xml文件。