Data from the underway system includes observations and measurements of meteorological (e.g. air temperature, atmospheric pressure, relative humidity, wind speed and direction) at 10m above sea level and oceanographic (e.g. sea surface temperature/salinity) at approximately 3m below surface at a per minute rate. Data has been collected in survey areas including the greater North Atlantic Ocean, Irish Sea, Saint Georges Channel, Celtic Sea, North Sea and Inner Seas off the West Coast of Scotland. Geographic coverage also includes areas around Newfoundland Canada. Data has been collected since the launch of the RV Celtic Explorer in May 2003. Underway near-surface measurements of sea temperature are typically made using the cooling water intake of a vessel using a thermosalinograph. Underway data collection has been initiated to create a long-run time series of sea surface temperature supporting knowledge and information on the physical oceanographic conditions of waters where the RV Celtic Explorer has undertaken marine surveys. Weather station data collected to support knowledge on meteorological conditions at sea. Data collection activity on-board Irelands largest national marine research vessel Celtic Explorer operated by PO Maritime Services on behalf of the Marine Institute. Data is not 100% complete for every research day of vessel activity due to technical issues with underway instrumentation. Coverage estimated at >95% research days at sea.