In-air time series for intercomparison of a 11 high dynamic range and autonomous ocean-light instruments (OptiCAL)

For calibration purposes 11 OptiCAL nodes were mounted on a calibration cage that was placed on the roof of a building to avoid shadowing. Data were recorded over three and a half days from 07.05.2020 to 11.05.2020 at Taynuilt in Scotland. The goal was to assess if OptiCAL nodes are sufficiently similar for applying a global / ensemble calibration or if each sensor should be calibrated individually.

The OptiCAL (Optical Chain And Logger) is an autonomous ice-tethered observatory for measuring the underwater light climate. It comprises of a spar buoy (containing Iridium and GPS antenna, logger/controller, Iridium modem and batteries) and a chain with “nodes” at certain depths. Each node carries three upward and three downward looking light sensors. For each direction two sensors have a gel filter, one blue and one orange while the third sensor is unfiltered. OptiCAL data are archived in a netCDF file as 'counts' from the sensors and are in units of millihertz [mHz]. See Schartmüller et al. (submitted for publication) for a detailed description of the instrument and the calibration for deriving EPAR [µmol m-2s-1] from the unfiltered channel.

The work was supported by three grants from the Norwegian Research Council: Arctic ABC (project no 244319, Arctic ABC Development (project no 245923), Deep Impact (project no 300333), and the Centre of Excellence AMOS (project no 223254).