Photogrammetric scans of aerial photographs of North American glaciers, 1977. Roll 5 tiffs

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.

## 介绍
1958年至1999年间，奥斯汀·波斯特（Austin Post）牵头开展了美国地质调查局（United States Geological Survey, USGS）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，同时也采集了单张倾斜影像与彩色影像。本次采集以北美冰川为核心对象，本平台提供的数字化成果旨在记录近50年来北美冰川发生的变化。本项目旨在将这些胶片影像中的数据以数字化格式留存，以供未来开展北美冰川变化相关分析研究。

## 文件结构
1. 第一层级包含1964年至1997年的影像元数据总数据集（nagapData.csv）以及一份用于指导数据检索与子集提取的R脚本（searchData.R）。fileLayout.pdf以可视化形式展示了文件结构与文件夹内容，此外还有三份按年代划分飞行路径信息的KML（Keyhole Markup Language, KML）文件。
2. 第二层级为影像拍摄年份。本次数据集涵盖1964年至1997年间的32个年份。大部分此类文件夹中包含奥斯汀·波斯特提供注释的JPEG（Joint Photographic Experts Group, JPEG）影像，同时还包含一份年度专属CSV（Comma-Separated Values, CSV）文件（YYYY.csv），用于存储全年的影像元数据，包括拍摄日期、胶卷编号、地点名称、经度、纬度、海拔、媒介类型与备注信息。总数据集nagapData.csv由各单独的"YYYY.csv"文件汇总整合而成。
3. 第三层级（即当前层级）存放冰川影像。该层级的文件夹按照相机胶卷编号（1、2等）与影像类型（缩略图、JPEG或TIFF（Tagged Image File Format, TIFF））进行区分，部分文件夹还包含基准影像与倾斜影像子文件夹。本层级主要存储航空影像的各类文件，包括缩略图、JPEG与TIFF格式文件。此外还包含一份针对每个胶卷的CSV元数据文件，内容涵盖拍摄日期、胶卷编号、地点名称、经度、纬度、海拔、媒介类型与备注信息；一份记录单张影像专属相机参数的文本文件（info.txt）；以及一份包含单张影像专属色彩信息与扫描仪参数的文本文件（histo.txt或matchReport.txt）。