Photogrammetric scans of aerial photographs of North American glaciers, 1977. 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.

## 介绍
1958年至1999年间，奥斯汀·波斯特（Austin Post）主持了美国地质调查局（United States Geological Survey, USGS）的北美冰川航空影像采集工作。本次采集的影像以垂直立体黑白影像为主，同时也包含单张倾斜影像与彩色影像。本数据集以北美冰川为研究对象，公开的数字化成果旨在记录过去50年间北美冰川的变化情况。本项目的核心目标是将这些胶片影像中的数据以数字化形式留存，以供未来开展北美冰川变化相关研究分析使用。

## 文件布局
1. 一级目录包含1964年至1997年的全局影像元数据集（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3个按年代划分飞行路径信息的KML文件。
2. 二级目录以影像拍摄年份命名。本次数据集涵盖1964年至1997年的32个拍摄年份。多数年份文件夹内包含奥斯汀·波斯特所标注的JPEG格式影像文件，同时还附带按年份命名的CSV文件（YYYY.csv），其中存储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、海拔、介质类型与备注信息。全局元数据集nagapData.csv即为所有单个YYYY.csv文件的整合汇总。
3. 冰川影像文件存储于三级目录（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TIFF）进行区分，部分文件夹还包含框标影像与倾斜影像的子文件夹。本层级主要存储航空影像文件，格式涵盖缩略图、JPEG与TIFF。此外还包含按胶卷划分的专属元数据CSV文件，内容包括拍摄日期、胶卷编号、地点名称、经度、纬度、海拔、介质类型与备注信息；另有单张影像专属的相机参数文本文件（info.txt），以及包含色彩信息与扫描仪参数的文本文件（histo.txt或matchReport.txt）。