The SolData optics table was equipped to measure: global irradiance (3 instruments), ultraviolet B (UVB), illuminance (lux), barometric pressure (hPa), background radiation (counts/10 min), sky luminance (cd/m2) and PAR (einstein/m2). These measurements have been described in other work [5]. The focus of this paper is on further analysis of the global solar irradiance data. Other research groups on board the research vessel contributed to another database, and this database is also accessible (5-minute values) including relative humidity, a parameter which will also receive attention in this paper.

2.3

Global solar irradiance

Figure 2: Global solar irradiance from Accra, Ghana, October 2006.

Figure 2 shows typical global irradiance data — in this case when the expedition was near the Ghanan city of Accra off the western coast of Africa. We have focused on days which were “clear”, i. e. cloud cover was so insignificant that a clear day global irradiance model could be fitted to the global irradiance data for a given day. A significant number of days during the eight month voyage of Galathea III were so clear, that this procedure was possible.