Photogrammetric scans of aerial photographs of North American glaciers, 1991. Roll 4 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.

### 数据集简介
1958年至1999年，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项目。本次采集的影像以垂直立体黑白影像为主，同时也收录了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，本次公开的数字化成果旨在记录近50年来这些冰川的演变过程。本项目的核心目标是将这些胶片影像中的原始数据以数字化格式永久保存，为后续北美冰川变化研究提供支撑。

### 文件布局
1. **一级目录**：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整体文件结构与目录内容；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。多数此类目录下存储有奥斯汀·波斯特标注的JPEG格式影像，同时还包含一个对应年份的专属元数据CSV文件（"YYYY.csv"），其中记录了全年所有影像的元数据，包括拍摄日期、胶卷编号、地点名称、经度、纬度、飞行高度、影像介质及备注信息。总数据集"nagapData.csv"即为所有单个"YYYY.csv"文件的聚合体。
3. **三级目录**：即当前层级，存储冰川影像。该层级的目录按相机胶卷编号（1、2等）与影像类型（缩略图、JPEG或TIF）进行划分，部分目录还包含框标影像与倾斜影像的子目录。本层级主要存储航空影像文件，格式包括缩略图、JPEG与TIF。此外还包含针对每个胶卷的专属元数据CSV文件（记录内容涵盖拍摄日期、胶卷编号、地点名称、经度、纬度、飞行高度、影像介质及备注），一份用于记录单张影像专属相机参数的文本文件（"info.txt"），以及一份用于记录单张影像色彩信息与扫描仪参数的文本文件（"histo.txt"或"matchReport.txt"）。