Alaska Landfast Ice Extent and Breakup Timing over 2000-2022

This dataset contains a landfast ice climatology calculated from MODIS imagery. For a complete description of the methods, please see Cooley and Ryan (2024), Community-scale changes to landfast ice along the coast of Alaska over 2000-2022, Environmental Research Letters, doi.org/10.1088/1748-9326/ad1c7b This dataset contains a shapefile “landfast_ice_edge_2000_2022.shp” of maximum ice edge positions derived from MODIS imagery. The ‘time period’ column refers to the 30-day period over which the edge position was calculated, specifically 1: March 1st to April 1st, 2: March 15th to April 15th and 3: April 1st to May 1st. For years with multiple lines and/or multiple time periods present in the dataset, we retain the maximum position in our analysis; in other words, we calculate the ice edge position based on the furthest line from the coast. This dataset also contains time series of seaward landfast ice edge (SLIE) position (distance to the ice edge from the coastline, in km) and breakup timing (in day of year). The ice edge position is calculated as the maximum ice edge distance from coastline using the ice edge shapefile described above. The breakup date is defined as the day when 75% of the area contained within the maximum ice edge position for that year reaches open water. This is corrected for cloud cover by assigning the actual breakup date as the midpoint between the first day when the ice was open water and the previous cloud-free observation. This uncertainty (in days) is recorded as “Breakup Uncertainty”. Any usage of this data should also cite Cooley and Ryan (2024). For any questions about the dataset, please reach out to Sarah Cooley at [e-mail]

本数据集包含基于MODIS影像反演得到的固定冰（landfast ice）气候学数据集。关于方法的完整说明，请参见Cooley与Ryan（2024）发表于《Environmental Research Letters》的论文《2000-2022年阿拉斯加沿岸固定冰的群落尺度变化》，DOI：10.1088/1748-9326/ad1c7b。

本数据集包含名为"landfast_ice_edge_2000_2022.shp"的矢量shapefile文件，存储了由MODIS影像提取的最大冰界位置。其中"time period（时间周期）"字段指代用于计算冰界位置的30天时段，具体包括：1. 3月1日至4月1日；2. 3月15日至4月15日；3. 4月1日至5月1日。若某一年份的数据集中存在多条冰界线和/或多个时间周期，本分析仅保留最大冰界位置，即基于距海岸最远的冰界线计算冰界位置。

本数据集还包含向海固定冰界（seaward landfast ice edge, SLIE）位置（以距海岸线的冰界距离计，单位：km）和解冻时间（以年中日数计）的时序数据。冰界位置通过上述冰界shapefile文件计算得到，为距海岸线最远的冰界距离。解冻日期定义为该年度最大冰界范围内75%的区域变为开阔水域的日期。为修正云覆盖带来的影响，将实际解冻日期设置为首次观测到开阔水域的日期与前一次无云观测日期的中点，该修正的不确定性（单位：天）以"Breakup Uncertainty（解冻不确定性）"字段记录。

使用本数据集需同时引用Cooley与Ryan（2024）的研究。若对本数据集有任何疑问，请联系Sarah Cooley，邮箱：[e-mail]。