UAV-derived Digital Surface Models and orthoimages for three alpine glaciers

UAV-derived DSMs and orthoimages Unmanned Aerial Vehicle (UAV) surveys were conducted between 2015 and 2016 on the Sankt Annafirn, Findelen- and Griesgletscher, situated in the Swiss Alps. Three surveys at the Sankt Annafirn allowed for a full glacier coverage, four surveys at Griesgletscher allowed an almost full glacier coverage and seven surveys at Findelengletscher allowed for a partial coverage of the glacier tongue (see individual datasets for exact extent). For each survey, a high resolution orthoimage and a Digital Surface Model (DSM) was created. UAV surveys: Prior flight, Ground Control Points (GCPs) were deployed on the glacier surface and measured with a differential GPS (Trimble R7 or Leica GPS 1200). They allowed precise georeferencing of the UAV-derived datasets. UAV flight plans were planned with the software *eMotion 2* and a SenseFly eBee was used as surveying platform. The images were then processed with the software Agisoft Photoscan Pro 1.1.6 . The location and dates of each survey can be found in the table together with the number of flights performed (Nflights), the number of acquired images (Nimages), the number of GCPs set (NGCPs) and the surveyed area. A folder for each dataset is available (see folder name in table), which contains: - An orthoimage *glacier_date_photoscan_oi_CH1903+_LV95_0.1m.tif* - A Digital Surface Model *glacier_date_photoscan_dsm_CH1903+_LV95_0.1m.tif* - The Agisoft Photoscan automatic processing report *glacier_date_photoscan_report.pdf* where: - *glacier* is the name of the surveyed glacier - *date* is the date of the UAV image acquisition - *photoscan* is the name of the photogrammetric software - *oi* or *dsm* the type of dataset - *CH1903+_LV95* is the coordinate system and datum of the dataset - *0.1m* is the resolution of the dataset in meter - *.tif* is the extention of the dataset Details about the UAV surveys, the image processing and the accuracy of the UAV-derived products can be found in this publication below. Paper Citation: - _Gindraux et al. 2017. Accuracy Assessment of Digital Surface Models from Unmanned Aerial Vehicles’Imagery on Glaciers, Remote Sensing, 9, 186, 1-15, [doi: 10.3390/rs9020186](https://doi.org/10.3390/rs9020186)._ The folder UAV_flight_paths.zip contains all UAV flights performed on the Sankt Annafirn, Findelengletscher and Griesgletscher. The flights were planned with the software eMotion2 and have the .afp extention.

无人机获取的数字表面模型与正射影像数据集说明：2015至2016年间，研究团队于瑞士阿尔卑斯山区的圣安娜菲尔恩冰川（Sankt Annafirn）、芬德伦冰川（Findelengletscher）与格里茨冰川（Griesgletscher）开展了无人驾驶航空器（Unmanned Aerial Vehicle, UAV）航拍调查。其中，圣安娜菲尔恩冰川共开展3次航拍，实现冰川全域覆盖；格里茨冰川开展4次航拍，实现近乎全域覆盖；芬德伦冰川开展7次航拍，仅覆盖冰川舌区域（具体范围详见各数据集文档）。

针对每一次航拍调查，均生成了高分辨率正射影像与数字表面模型（Digital Surface Model, DSM）。

### 无人机航拍流程
航拍作业前，研究人员在冰川表面布设地面控制点（Ground Control Points, GCPs），并采用差分GPS（Trimble R7或Leica GPS 1200）完成测量，以此实现无人机获取数据的精准地理配准。航拍飞行计划由*eMotion 2*软件制定，航拍平台采用SenseFly eBee无人机。后续影像数据通过Agisoft Photoscan Pro 1.1.6软件完成处理。

### 数据集信息与文件结构
所有调查的点位、日期、飞行架次（Nflights）、获取影像数量（Nimages）、布设地面控制点数量（NGCPs）以及调查区域均可在附表中查询。每个数据集对应一个专属文件夹（文件夹名称详见附表），文件夹内包含以下文件：
1. 正射影像文件：`glacier_date_photoscan_oi_CH1903+_LV95_0.1m.tif`
2. 数字表面模型文件：`glacier_date_photoscan_dsm_CH1903+_LV95_0.1m.tif`
3. Agisoft Photoscan自动处理报告：`glacier_date_photoscan_report.pdf`

各文件名字段含义说明如下：
- `glacier`：被调查冰川的名称
- `date`：无人机影像获取日期
- `photoscan`：摄影测量软件名称
- `oi`或`dsm`：数据集类型
- `CH1903+_LV95`：数据集采用的坐标系与基准面
- `0.1m`：数据集的空间分辨率（单位：米）
- `.tif`：数据集文件扩展名

### 相关参考文献
有关无人机航拍流程、影像处理方法以及无人机产出产品的精度详情，可参阅下述论文：
> Gindraux等，2017年。《冰川无人机影像数字表面模型精度评估》，《遥感》，9卷，186期，1-15页，[doi: 10.3390/rs9020186](https://doi.org/10.3390/rs9020186)。

### 附加航线数据
文件夹`UAV_flight_paths.zip`包含了圣安娜菲尔恩冰川、芬德伦冰川与格里茨冰川的所有无人机飞行航线数据，该类航线文件由eMotion2软件生成，文件扩展名为`.afp`。