Data from: Meltwater ponding has an underestimated radiative effect on the surface of the Greenland Ice Sheet

These datasets include 1) surface water and surface albedo data from satellite remote sensing, 2) near-surface air temperature and downward shortwave radiation data from atmospheric reanalysis, and 3) high-resolution imagery from done surveys over the Greenland Ice Sheet.

The surface water data were derived from Sentinel-2 by Zhang et al. (2023). The albedo data are from the MCD43A3 version 6.1 product derived from the MODerate resolution Imaging Spectroradiometer (MODIS) onboard NASA’s Aqua and Terra satellites. The data represent two distinct time periods: Jul 25–30, 2018 and Jul 29–Aug 5, 2019 when most of the imagery was acquired. We resampled both surface water and surface albedo data onto the ISMIP6 grid by averaging values within each target grid cell. The ISMIP6 grid has an NSIDC Sea Ice Polar Stereographic North (EPSG:3413) projection and a grid cell resolution of 1 × 1 km.

The near-surface air temperature and downward all-sky shortwave radiation data are derived from the MERRA-2 radiation diagnostics product (M2T1NXRAD). The data represent summer means for the 2002-2023 period. We statistically downscaled both variables from 0.625 x 0.5° resolution to the ISMIP6 1 × 1 km grid following an elevation-based approach (Ryan et al., 2024).

The high-resolution imagery was acquired using a fixed-wing drone similar to that described by Ryan et al. (2015). The drone collected imagery at two separate field sites. The first site includes both Russell Glacier and Isunguata Sermia (180 km2) with an elevational range of 150–660 m a.s.l. During six surveys, the drone collected 9,732 overlapping images of glacier surface on Jul 11–12, 2015. The second site (110 km2) is situated in the dark zone with an elevational range of 1,170–1,290 m a.s.l. Here the drone collected a total of 3,795 images during three surveys between Jul 20–22, 2015. We used Agisoft Metashape Pro v2.2.0 to generate orthomosaics from the overlapping aerial imagery. The final products have a spatial resolution of 0.30 m.

We mapped meltwater ponding in the orthomosaic produced over the dark zone (1,170–1,290 m a.s.l.) using a semi-automated classification approach described in the article. We mapped meltwater over Russell Glacier and Isunguata Sermia by manually digitized ponded areas using the Geo-SAM QGIS plugin, an interactive segmentation tool based on the Segment Anything Model (SAM) foundation AI model. The final water maps are provided as shapefiles.

Ryan, J. C. et al. (2015), UAV photogrammetry and structure from motion to assess calving dynamics at Store Glacier, a large outlet draining the Greenland ice sheet. The Cryosphere 9, 1–11.

Ryan, J. C. (2024), Contribution of surface and cloud radiative feedbacks to Greenland Ice Sheet meltwater production during 2002–2023. Commun. Earth Environ. 5, 1–9.

Zhang, W. et al. (2023), Pan-Greenland mapping of supraglacial rivers, lakes, and water-filled crevasses in a cool summer (2018) and a warm summer (2019). Remote Sens. Environ. 297, 113781.

本数据集包含三类数据：1）卫星遥感获取的地表水与地表反照率数据；2）大气再分析资料中的近地表气温与全天空下行短波辐射数据；3）针对格陵兰冰盖开展无人机航测获取的高分辨率影像。

地表水数据由Zhang等人（2023）基于哨兵-2号（Sentinel-2）卫星数据反演得到。地表反照率数据来自MCD43A3 6.1版产品，该产品由搭载于美国国家航空航天局（NASA）Aqua与Terra卫星的中分辨率成像光谱仪（MODerate resolution Imaging Spectroradiometer, MODIS）生成。本次使用的数据覆盖两个典型时段：2018年7月25日至30日，以及2019年7月29日至8月5日，该时段内绝大多数影像完成采集。我们将地表水与地表反照率数据重采样至冰盖模式比较计划6（ISMIP6）网格，通过对每个目标网格单元内的数值取平均实现重采样。该ISMIP6网格采用美国国家冰雪数据中心（NSIDC）海冰北极立体投影（EPSG:3413），网格单元分辨率为1×1千米。

近地表气温与全天空下行短波辐射数据源自MERRA-2辐射诊断产品（M2T1NXRAD）。数据为2002-2023年夏季的平均值。我们采用基于高程的统计降尺度方法（Ryan等人，2024），将这两个变量从原0.625×0.5°的分辨率重采样至ISMIP6的1×1千米网格。

高分辨率影像通过固定翼无人机获取，其参数与Ryan等人（2015）描述的机型一致。无人机在两个独立野外站点开展航测：第一站点涵盖罗素冰川（Russell Glacier）与伊松瓜塔塞尔米亚冰川（Isunguata Sermia），总面积180平方千米，海拔范围为150~660米。2015年7月11日至12日期间，无人机通过6次航测共采集了9732张重叠的冰川地表影像。第二站点面积为110平方千米，位于冰盖暗区，海拔范围为1170~1290米。2015年7月20日至22日期间，无人机通过3次航测共采集了3795张影像。我们使用Agisoft Metashape Pro v2.2.0软件对重叠航空影像进行处理，生成正射影像镶嵌图，最终产品的空间分辨率为0.30米。

我们采用本文所述的半自动分类方法，对暗区（海拔1170~1290米）的正射影像镶嵌图进行冰面融水积水制图。针对罗素冰川与伊松瓜塔塞尔米亚冰川，我们借助基于分段任意模型（Segment Anything Model, SAM）的交互式分割工具Geo-SAM QGIS插件，通过手动数字化融水洼区域完成制图。最终的地表水分布图以形状文件（shapefiles）格式提供。

参考文献：
Ryan, J. C. 等（2015）：《无人机摄影测量与运动恢复结构法评估格陵兰冰盖大型出口冰川Store Glacier的崩解动力学》，《冰冻圈》（*The Cryosphere*），9卷，1-11页。
Ryan, J. C.（2024）：《2002-2023年地表与云辐射反馈对格陵兰冰盖融水产生的贡献》，《通讯-地球与环境》（*Commun. Earth Environ.*），5卷，1-9页。
Zhang, W. 等（2023）：《2018年凉夏与2019年暖夏期间格陵兰全境冰面河流、湖泊与充水裂缝的制图》，《遥感环境》（*Remote Sens. Environ.*），297卷，113781页。