3.1.1. PROMICE Measurements

PROMICE AWS (automatic weather station) is distributed in the ablation zone of Greenland. The surface types viewed are a mixture of snow patches, ice with time-varying physical parameters, and surface ponds, especially during the summer melt season [31,34–37], which may optically resemble

sea-ice surfaces under certain conditions. Therefore, the data was used as a substitute for sea-ice albedo measurements.

The newly-developed PROMICE sites provide high-quality measurements due to their continuous maintenance. The PROMICE automatic weather station (AWS) network currently consists of eight regions each with a minimum of two stations at a variety of elevations on the Greenland ice sheet (the lower one is labeled '\_L' and the upper one '\_U'). Most stations are located in the ablation area and are thus transitioning from snow-covered to bare ice surfaces through the melt season. Our comparison was applied to 18 PROMICE sites, as shown in Table 1, from January 2012 to June 2017. In each month, the VSIA granules during 11:00~13:00 (local time) on the 15th day were compared with the ground observations closest in time.

**Table 1.** The information of the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) stations.

