Photogrammetric scans of aerial photographs of North American glaciers, 1991. Roll 2 thumbnails

Introduction: Between 1958 and 1999, Austin Post led the USGS collection of aerial imagery of North American glaciers. These images are primarily vertical stereo black and white images, although single oblique images, as well as color images have been collected. The glaciers of North America were the subjects, and the digital products made available here serve to document the changes that have occurred to the glaciers over the past 5 decades. The purpose of this project is to preserve the data contained within these film images in a digital format for future analysis of North American glacier change. File Layout: 1. The first level contains an overall data set of image metadata from 1964 - 1997 (nagapData.csv) and an R script (searchData.R) with instructions on how to search and subset the data. fileLayout.pdf shows the file structure and folder contents visually. There are also three kml files with flight path information by decade. 2. The second level is the year in which the pictures were taken. There are 32 years with images from 1964 – 1997. The majority of these folders are jpegs with notes provided by Austin Post. They also contain a year-specific csv (YYYY.csv) that contains image metadata for the entire year (date, roll numbers, location name, longitude, latitude, altitude, media, and comments). The overall data set (nagapData.csv) is the aggregate of each individual “YYYY.csv” file. 3. The glacier photos are located at the third level (this level). The folders at this level are distinguished by camera roll number (1, 2, etc.), and image type (thumbnail, jpeg, or tif); some also contain fiducial and oblique image folders. This level primarily contains image files of aerial photos as either thumbnails, jpegs, or tifs. It also includes a csv with image metadata specific to each roll (date, roll numbers, location name, longitude, latitude, altitude, media, and comments), a text file (info.txt) with camera specifications unique to each image, and a text file (histo.txt or matchReport.txt) with color information and scanner specifications unique to each image.

引言：1958年至1999年间，奥斯汀·波斯特（Austin Post）牵头负责美国地质调查局（USGS）的北美冰川航空影像采集工作。该批影像以垂直立体黑白影像为主体，同时亦采集了单张倾斜影像与彩色影像。本数据集的研究对象为北美冰川，此处公开的数字化成果旨在记录近50年来该区域冰川的演变情况。本项目的核心目标是将这些胶片影像中的数据以数字化格式永久保存，以供未来开展北美冰川变化相关研究分析使用。

文件结构：
1. 第一层级包含1964年至1997年的影像元数据集（nagapData.csv），以及一份用于指导数据检索与子集筛选的R脚本（searchData.R）。fileLayout.pdf以可视化形式展示了整体文件结构与文件夹内容。此外还包含三份按十年划分的飞行路径信息KML文件。
2. 第二层级以影像拍摄年份命名。1964年至1997年间共有32个年份包含可用影像。此类文件夹中大多存储着奥斯汀·波斯特标注的JPEG格式影像文件，同时还包含一份对应年份的专属CSV文件（YYYY.csv），其中收录了该年度全部影像的元数据，包括拍摄日期、胶卷编号、地点名称、经度、纬度、拍摄高度、介质类型及备注信息。整体数据集文件nagapData.csv即为所有单个"YYYY.csv"文件的汇总集合。
3. 冰川影像存储于第三层级（即当前层级）。该层级的文件夹以相机胶卷编号（1、2等）与影像类型（缩略图、JPEG或TIF）进行分类命名，部分文件夹还包含框标影像与倾斜影像子文件夹。本层级主要存储航空照片的影像文件，格式涵盖缩略图、JPEG及TIF。此外还包含一份针对每个胶卷的专属影像元数据CSV文件（包含拍摄日期、胶卷编号、地点名称、经度、纬度、拍摄高度、介质类型与备注信息）、一份记录各影像专属相机参数的文本文件（info.txt），以及一份记录各影像专属色彩信息与扫描仪参数的文本文件（histo.txt或matchReport.txt）。