Cloud Fraction Estimates from Saildrone Sky Cameras during ATOMIC

Cloudiness is an essential metric of the climate system yet it has previously been difficult to measure from autonomous ocean vehicles. To add more capability to the uncrewed surface vehicle (USV) Saildrone, we develop a cloud fraction algorithm that processes upward-looking visible sky camera images taken atop the Saildrone. Images were collected and tested during the 2020 Atlantic Tradewind OceanAtmosphere Mesoscale Interaction Campaign (ATOMIC) in the Northwest tropical Atlantic. The USV Saildrones were operating in the same region as the NOAA research ship Ronald H. Brown. Cloud fraction estimates were similar from the ship-basd ceilometer and processed sky camera images taken from the same region. Relationships between cloud fraction and surface radiation are similar between the ship and Saildrone. Therefore, the cloud fraction sky camera image processing technique appears robust for further application and analysis of Saildrone data during ATOMIC and other field campaigns focused on weather, climate, and cloudiness.