SiDroForest: Orthomosaics, SfM point clouds and products from aerial image data of expedition vegetation plots in 2018 in Central Yakutia and Chukotka, Siberia

This orthomosaics and Structure from Motion (SfM) point clouds dataset is a part of the SiDroForest data collection (van Geffen et al., 2021). The aim of SiDroForest is to gain a clear picture of the current vegetation dynamics in the pan-arctic region of Siberia. The dataset presented here contains orthomosaics and structure from motion (SfM) point clouds and point cloud products for plots visited in Siberia during a 2-month fieldwork expedition in 2018 by the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research in Germany (Kruse et al., 2019).
During the fieldwork, 53 vegetation plots were covered by Unmanned Aerial Vehicle (UAV) flights and Red Green Blue (RGB) photographs were taken with a consumer grade DJI Phantom 4 quadcopter and MAPIR Survey3W RGNIR camera with a standardized flight plan (double-gridded in near-nadir position and circular facing the plot center at take-off elevation) on a 50 x 50 m area (further details in Kruse et al., 2019, Brieger et al., 2019).
From these UAV images, SfM point clouds and orthoimages were constructed. The UAV data and the products that were constructed are described below.

Data Collection
Because of the availability of multiple overlapping images from different camera viewpoints, point cloud processing and generation of 3-dimensional (3D) products and successive generation of orthoimages were possible. We manually rejected images that have been taken during take-off and landing, and blurry, under- or overexposed images from further processing. The remaining images were then used to generate the 3D point cloud and related products directly from the point cloud data.

本数据集包含正射镶嵌影像（orthomosaics）与运动恢复结构（Structure from Motion, SfM）点云，属于SiDroForest数据采集项目（van Geffen等，2021）的一部分。SiDroForest项目的目标是清晰掌握西伯利亚泛北极区域当前的植被动态。本次发布的数据集涵盖2018年德国阿尔弗雷德·魏格纳研究所·亥姆霍兹极地与海洋研究中心（Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research）在西伯利亚开展的为期2个月野外考察中所踏勘的53个植被样地的相关数据，包括正射镶嵌影像、运动恢复结构点云及点云衍生产品（Kruse等，2019）。

野外考察期间，研究团队使用消费级大疆（DJI）精灵4四旋翼无人机与MAPIR Survey3W RGNIR相机，按照标准化飞行计划在50×50米的样地范围内开展无人机（Unmanned Aerial Vehicle, UAV）飞行作业，采集红绿蓝（Red Green Blue, RGB）影像；飞行计划采用近天顶方向双网格布局，且在起飞高度下环绕朝向样地中心（详细说明参见Kruse等，2019；Brieger等，2019）。

基于上述无人机影像，研究人员构建了运动恢复结构（SfM）点云与正射影像。下文将对本次采集的无人机数据及衍生产品进行详细说明。

数据采集
由于采集了多组不同拍摄视角的重叠影像，因此可开展点云处理、三维（3-dimensional, 3D）产品生成，并后续生成正射影像。研究人员人工剔除了起飞、降落阶段拍摄的影像，以及模糊、欠曝光或过曝光的影像，不用于后续处理流程。剩余影像随后将直接用于三维点云及相关衍生产品的生成。