Orthorectification and Mosaicking of Color Aerial Photography for the Main Eight Hawaiian Islands: Maui (313-0524)

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.

本数据集依托Habitat Digitizer扩展模块（Habitat Digitizer extension），通过对航空照片与高光谱影像开展目视解译，完成了夏威夷主要岛屿的生境地图绘制。航空照片可为自然资源管理者与科研人员提供生境位置及分布范围的精准记录，是极具实用价值的研究工具。然而，航空照片会因拍摄角度、镜头特性以及地形起伏位移等因素产生空间畸变，若在分析阶段未对其进行校正，将导致面积、距离及其他空间参数的测量结果出现偏差。图像内部的这类尺度畸变可通过正射校正（orthorectification）予以消除：正射校正过程中，需通过算法对航空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拼接数字镶嵌图，且整张镶嵌图的尺度保持一致。近岸地物的地理配准精度通常较高，而远海地物的配准精度则相对较低；若原始摄影画幅未包含陆地，则仅通过运动学GPS定位点与影像连接点完成影像的地理配准。正射校正镶嵌图制作完成后，影像解译人员可借助Habitat Digitizer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。