Photogrammetric scans of aerial photographs of North American glaciers, 1972. 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.

## 数据集简介
1958年至1999年间，奥斯汀·波斯特（Austin Post）主导了美国地质调查局（United States Geological Survey, USGS）的北美冰川航空影像采集工作。该类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。本数据集以北美洲冰川为研究对象，此处提供的数字化成果旨在记录近50年来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。

## 文件结构
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。另有三份按年代划分的飞行路径信息KML（Keyhole Markup Language）文件。
2. 二级目录以影像拍摄年份命名，涵盖1964年至1997年间共32个年份的影像数据。多数此类目录中包含由奥斯汀·波斯特撰写注释的JPEG（Joint Photographic Experts Group）影像文件，同时还附带一份对应年份的元数据CSV文件（`YYYY.csv`），该文件包含全年影像的元数据信息，具体包括拍摄日期、胶卷编号、地点名称、经度、纬度、海拔、影像介质与备注说明。总数据集`nagapData.csv`即为所有单年度`YYYY.csv`文件的汇总。
3. 冰川影像位于三级目录（即当前层级）。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TIFF（Tagged Image File Format））进行划分，部分目录还包含基准标记（fiducial）影像与倾斜影像子目录。本层级主要存储各类航空影像文件，格式包括缩略图、JPEG与TIFF。此外还包含一份针对单卷胶卷的元数据CSV文件，其内容涵盖拍摄日期、胶卷编号、地点名称、经度、纬度、海拔、影像介质与备注说明；另有一份文本文件`info.txt`，用于存储单张影像专属的相机参数信息；以及一份`histo.txt`或`matchReport.txt`文本文件，用于存储单张影像专属的色彩信息与扫描仪参数。