Gridded segments of sea-ice or snow surface elevation and freeboard from helicopter-borne laser scanner during the MOSAiC expedition flight 20200928_02, version 1

This data set is a higher-processing-level version of Geolocated sea-ice or snow surface elevation point clouds from helicopter-borne laser scanner during the MOSAiC expedition, version 1 (Jutila et al., 2022; doi:10.1594/PANGAEA.950509), where the surface elevation point cloud has been converted to freeboard using automatic open water detection scheme and projected onto a regular 0.5-meter grid. The data were collected using a near-infrared, line-scanning Riegl VQ-580 airborne laser scanner (hdl:10013/sensor.7ebb63c3-dc3b-4f0f-9ca5-f1c6e5462a31 & hdl:10013/sensor.7a931b33-72ca-46d0-b623-156836ac9550) mounted in a helicopter along the MOSAiC drift from the north of the Laptev Sea, across the central Arctic Ocean, and towards the Fram Strait from September 2019 to October 2020. The flights are both small scale, ~5x5 km grid patterns mainly over the central observatory, and large scale, few tens of km away from RV Polarstern, triangle patterns, or transects. The gridded data are stored in 30-second along-track segments in netCDF format. For the small scale grid flights, the data are drift corrected using the position and heading data of RV Polarstern and elevation offset corrected using overlapping segments to overcome degraded GPS altitude data >85°N. Open water points are identified to derive a freeboard estimate from the surface elevations. For the flights with degraded GPS altitude quality, we provide only a freeboard estimate (grid pattern flights) or no freeboard (transects). The gridded 30-s segments include as data variables: surface elevation, freeboard (estimate), freeboard uncertainty, estimated sea surface height, surface reflectance, echo width, and number of points used in the interpolation. In addition, list of detected open water points and an overview figure of each flight is provided.本数据集为MOSAiC科考期间机载直升机激光扫描仪获取的地理定位海冰或积雪表面高程点云的高阶处理版本（版本1，Jutila等，2022；doi:10.1594/PANGAEA.950509），其中表面高程点云已通过自动开阔水域检测方案转换为干舷（freeboard），并投影至0.5米规则网格。数据集采用搭载于直升机的近红外线扫描Riegl VQ-580机载激光扫描仪（hdl:10013/sensor.7ebb63c3-dc3b-4f0f-9ca5-f1c6e5462a31 与 hdl:10013/sensor.7a931b33-72ca-46d0-b623-156836ac9550）采集，采集轨迹沿MOSAiC科考漂流路线，于2019年9月至2020年10月间从拉普捷夫海北部出发，穿越北冰洋中部，最终向弗拉姆海峡行进。本次飞行任务涵盖两种尺度：小尺度任务以约5×5千米的网格模式作业，主要覆盖中央观测站区域；大尺度任务则在距离极星号（RV Polarstern）科考船数十公里外开展，采用三角模式或断面航线。网格化数据以沿轨30秒分段的netCDF（网络通用数据格式）格式存储。针对小尺度网格飞行任务，研究团队使用极星号的位置与航向数据进行漂移校正，并通过重叠分段进行高程偏移校正，以解决北纬85°以上区域GPS高程数据质量下降的问题。通过识别开阔水域点，可从表面高程数据中推导干舷估算值。对于GPS高程数据质量不佳的飞行任务，仅为网格模式飞行任务提供干舷估算值，断面航线任务则不提供干舷数据。网格化30秒分段包含以下数据变量：表面高程、干舷（估算值）、干舷不确定性、估算海表面高度、表面反射率、回波宽度以及插值所用的点数。此外，数据集还提供了检测到的开阔水域点列表，以及每次飞行任务的概览图。