Gridded segments of sea-ice or snow surface elevation and freeboard from helicopter-borne laser scanner during the MOSAiC expedition flight 20200423_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考察（北极气候研究多学科漂流观测站Multidisciplinary drifting Observatory for the Study of Arctic Climate）期间，由直升机搭载激光扫描仪获取的地理定位海冰或雪面高程点云的高阶处理版本，版本1（Jutila等，2022；doi:10.1594/PANGAEA.950509）。本数据集通过自动敞开水域检测方案将面高程点云转换为冰露高（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（持久标识符hdl:10013/sensor.7ebb63c3-dc3b-4f0f-9ca5-f1c6e5462a31与hdl:10013/sensor.7a931b33-72ca-46d0-b623-156836ac9550），于2019年9月至2020年10月期间，沿MOSAiC漂流轨迹从拉普捷夫海北部横穿北冰洋中部，向弗拉姆海峡方向开展飞行作业。

飞行任务分为两类：小范围飞行主要覆盖中部观测站，采用约5×5千米的网格布设模式；大范围飞行距离极星号（RV Polarstern）科考船数十千米，采用三角布设模式或断面航线模式。

网格化数据以沿轨30秒分段的netCDF格式存储。针对小范围网格飞行任务，借助极星号的位置与航向数据完成漂移校正，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。

通过识别敞开水域点，可从面高程数据中推导冰露高估算值。对于GPS高程质量退化的飞行任务，仅为网格模式飞行提供冰露高估算值，断面航线飞行则不提供冰露高数据。

网格化30秒分段包含以下数据变量：面高程、冰露高（估算值）、冰露高不确定性、估算海面高度、面反射率、回波宽度以及插值所用点数。此外，本数据集还附带检测到的敞开水域点列表，以及各次飞行任务的概况图。