Photogrammetric scans of aerial photographs of North American glaciers, 1992

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 (this 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. 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) with color information unique to each image.

## 引言
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。该类影像以垂直立体黑白影像为主，同时亦采集了单幅倾斜影像与彩色影像。本次数据集以北美冰川为研究对象，此处公开的数字化产品旨在记录近50年来这些冰川发生的变化。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。

## 文件布局说明
1. 第一层级包含1964年至1997年的影像元数据总集（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. 第二层级（即当前层级）为影像拍摄年份文件夹。本次数据集涵盖1964年至1997年间的32个拍摄年份。多数文件夹内存储的是奥斯汀·波斯特附带标注说明的JPEG影像，同时还包含针对该年度的专属元数据CSV文件（YYYY.csv），其中记录了全年影像的元数据信息，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。总数据集文件nagapData.csv即为各年度“YYYY.csv”文件的汇总。
3. 冰川影像存储于第三层级。该层级的文件夹按相机胶卷编号（1、2等）与影像类型（缩略图、JPEG或TIF）进行划分，部分文件夹还包含框标影像与倾斜影像文件夹。该层级主要存储航空照片的影像文件，格式包括缩略图、JPEG或TIF。此外还包含针对每个胶卷的专属元数据CSV文件（记录内容为拍摄日期、胶卷编号、地点名称、经度、纬度、海拔、媒介类型与备注）、一份存储单张影像专属相机参数的文本文件（info.txt），以及一份存储单张影像专属色彩信息的文本文件（histo.txt）。