Observed ocean surface albedo from a fixed offshore platform

The ocean surface albedo (OSA) is an important parameter in numerical ocean models and air‒sea heat flux calculations. Radiation observations were conducted to study the OSA in the northern South China Sea using a fixed offshore tower-based platform. The platform was located at 21.44° N, 111.39° E, with an average water depth of approximately 16 m. It consisted of a main tower and two auxiliary towers. The auxiliary towers were approximately 6 m from the main tower and their lower edges were approximately 6 m from the mean sea surface.

A four-component net radiometer (CNR4) was installed on the lower edge of the southeast auxiliary tower through a 2-m long boom to simultaneously measure the upward and downward broadband solar radiation having spectral bands between 305 and 2800 nm. A bottom-mounted Nortek acoustic Doppler current profiler was used to measure surface waves. Other ancillary meteorological instruments were used to measure meteorological parameters, including wind speed and water vapor pressure.

The observation period lasted from September 2017 to December 2018. The measured broadband radiation was collected in 30-min segments. To obtain an accurate and reliable radiation dataset, three specific types of data were removed from the dataset: (1) local afternoon data; (2) data with solar altitude angles < 10°; (3) data with downward solar radiation of < 30 W m−2. After this quality control, 2433 segments of data can be used to study the OSA.