Gridded segments of sea-ice or snow surface elevation and freeboard from helicopter-borne laser scanner during the MOSAiC expedition flight 20200321_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科考期间机载激光扫描仪获取的地理定位海冰/雪面高程点云的高阶处理版本（版本1，Jutila等，2022；doi:10.1594/PANGAEA.950509），通过自动开阔水域检测方案将原始表面高程点云转换为冰面干舷（freeboard），并投影至规则0.5米网格中。数据采集使用搭载于直升机的近红外线扫描Riegl VQ-580机载激光扫描仪（标识符：hdl:10013/sensor.7ebb63c3-dc3b-4f0f-9ca5-f1c6e5462a31 与 hdl:10013/sensor.7a931b33-72ca-46d0-b623-156836ac9550），随MOSAiC科考漂流航线采集，航线从拉普捷夫海北部出发，横跨北冰洋中部，最终抵达弗拉姆海峡，采集时段为2019年9月至2020年10月。本次飞行任务分为两种尺度：小尺度任务以约5×5公里的网格模式为主，覆盖中部观测站点；大尺度任务则在距离极地斯特恩号（RV Polarstern）数十公里外开展，采用三角网格模式或断面航线模式。网格化数据以沿轨30秒分段的形式存储于netCDF格式文件中。针对小尺度网格飞行任务，数据集采用极地斯特恩号的位置与航向数据进行漂移校正，并通过重叠分段对高程偏移进行校正，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冰面干舷估算值。对于GPS高程数据质量不佳的飞行任务，仅提供冰面干舷估算值（网格模式飞行任务）或不提供冰面干舷数据（断面航线任务）。网格化30秒分段数据包含以下数据变量：表面高程、冰面干舷（估算值）、冰面干舷不确定性、估算海面高度、表面反射率、回波宽度以及插值所用点数。此外，数据集还附带检测到的开阔水域点列表，以及每一次飞行任务的概览图。