Gridded segments of sea-ice or snow surface elevation and freeboard from helicopter-borne laser scanner during the MOSAiC expedition flight 20200806_01, 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.

本数据集为北极气候研究多学科漂流观测实验（MOSAiC）期间，由机载直升机激光扫描仪获取的地理定位海冰与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）。该数据集通过自动开阔水域检测算法将表面高程点云转换为海冰干舷（freeboard），并投影至规则0.5米网格。

数据采集采用搭载于直升机的近红外线扫描型Riegl VQ-580机载激光扫描仪（永久标识符hdl:10013/sensor.7ebb63c3-dc3b-4f0f-9ca5-f1c6e5462a31 与 hdl:10013/sensor.7a931b33-72ca-46d0-b623-156836ac9550），沿MOSAiC漂流轨迹从拉普捷夫海北部穿越北极中央海域，于2019年9月至2020年10月向弗拉姆海峡方向开展作业。

飞行任务涵盖两种尺度：小尺度任务采用约5×5千米的网格模式，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）科考船数十千米的区域开展，采用三角形模式或断面航线。

网格化数据以netCDF格式存储为沿航迹的30秒分段文件。针对小尺度网格飞行任务，采用极星号科考船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高程数据质量退化的问题。

本数据集通过识别开阔水域点，从表面高程数据中推算海冰干舷估值。对于GPS高程数据质量退化的飞行任务，仅为网格模式飞行任务提供海冰干舷估值，断面航线任务则不提供干舷数据。

网格化30秒分段文件包含以下数据变量：表面高程、海冰干舷（估值）、干舷不确定性、估算海面高度、表面反射率、回波宽度以及插值所用的点数。此外，还附带检测到的开阔水域点列表与每次飞行任务的概览图。