Orthorectification and Mosaicking of Color Aerial Photography for the Main Eight Hawaiian Islands: Molokai (328w-0516)

Habitat maps of the main Hawaiian Islands were created by visual interpretation of aerial photos and hyperspectral imagery using the Habitat Digitizer extension. Aerial photographs are valuable tools for natural resource managers and researchers since they provide an excellent record of the location and extent of habitats. However, spatial distortions in aerial photographs due to such factors as camera angle, lens characteristics, and relief displacement must be accounted for during analysis to prevent incorrect measurements of area, distance, and other spatial parameters. These distortions of scale within an image can be removed through orthorectification. During orthorectification, digital scans of aerial photos are subjected to algorithms that eliminate each source of spatial distortion. The result is a georeferenced digital mosaic of several photographs with uniform scale throughout the mosaic. Features near land are generally georeferenced with greater accuracy while the accuracy of features away from land is generally not as good. Where no land is in the original photographic frame only kinematic GPS locations and image tie points were used to georeference the images. After an orthorectified mosaic is created, photointerpreters can accurately and reliably delineate boundaries of features in the imagery as they appear on the computer monitor using a software interface such as the Habitat Digitizer.

本研究借助生境数字化仪（Habitat Digitizer）扩展工具，通过航空摄影照片与高光谱影像的目视解译，完成了夏威夷主要岛屿的生境地图制作。航空摄影照片可精准记录生境的位置与分布范围，是自然资源管理者与科研人员极具价值的研究与管理工具。然而，航空摄影照片会因相机倾角、镜头特性以及地形起伏像点位移等因素产生空间畸变，分析过程中必须对这类畸变进行校正，否则将导致面积、距离及其他空间参数的测量结果出现偏差。影像内的尺度畸变可通过正射校正予以消除：在正射校正环节中，需通过专用算法对航空摄影照片的数字扫描件进行处理，以消除所有来源的空间畸变，最终得到经过地理配准的多幅照片数字镶嵌图，且整张镶嵌图的比例尺保持一致。紧邻陆地的地物通常可获得更高的地理配准精度，而远离陆地的地物配准精度则相对较低。若原始摄影画幅未包含陆地，则仅可通过动态GPS定位数据与影像连接点对影像进行地理配准。完成正射校正镶嵌图制作后，影像解译人员可借助生境数字化仪等软件界面，在计算机显示器上精准且可靠地勾绘影像中各类地物的边界。