Advancing Arctic summer sea ice freeboard from ICESat-2

The ICESat-2 laser altimeter was launched in 2018 and has been measuring surface elevation used to determine sea ice thickness. The sea ice freeboards during winter (November-April) show strong agreement with in-situ observations. However, meltwater ponds accumulating on the sea ice over summer have prevented generating valid sea ice thickness observations from ICESat-2 in the summer months. Melt ponds hinder the classification of lead surfaces, leading to errors in the sea surface reference.

Utilizing more than 80 Sentinel-2 optical images coinciding within 5 minutes with ICESat-2 tracks, we have trained a Gaussian Mixture clustering algorithm that correctly classifies laser returns throughout the melt season. On testing images, the newly developed classification performs considerably better than the ATL07 classification, which was designed to be applied over winter conditions. The new classification was used to create an ICESat-2 summer laser freeboard dataset. The freeboards were validated with NASA's summer airborne lidar data acquisition campaign over July 2022.

The new summer freeboard dataset captures the melt season well, showing a quick decrease in freeboard during the melt of the snowpack in May and June and a slight increase at the start of autumn in September.

The summer sea ice freeboard dataset from ICESat-2 provides promising opportunities to calculate year-round sea ice thickness and volume, improve seasonal predictability, validate and improve the representation of sea ice in coupled climate models, and improve shipping risk assessment.