WOA18 A5B7 Sound Velocity Datasets (Annual, Seasonal and Monthly) 1 degree resolution

This dataset contains derived climatological seawater sound-speed fields based on temperature and salinity from the World Ocean Atlas 2018 (WOA18), produced by NOAA NCEI using quality-controlled observations from the World Ocean Database 2018. WOA18 supplies objectively analysed climatological fields describing the spatial and temporal distribution of ocean properties. Period code A5B7 identifies the 2005–2017 reference interval, a single 13-year climatological period rather than the longer WOA18 decav average. Resolution code 01 specifies a 1° latitude × 1° longitude grid, equivalent to 60 angular minutes in both directions. Temporal identifiers distinguish annual climatology (00); monthly climatologies (01 January, 02 February, 03 March, 04 April, 05 May, 06 June, 07 July, 08 August, 09 September, 10 October, 11 November and 12 December); and seasonal climatologies (13 January–March, 14 April–June, 15 July–September and 16 October–December). These seasons correspond to Northern Hemisphere winter, spring, summer and autumn. Annual and seasonal source temperature and salinity fields contain 102 standard depth levels from 0 to 5500 m, while monthly fields contain 57 levels from 0 to 1500 m. Actual valid vertical coverage varies geographically according to ocean depth and source masking. Sound-speed fields for the WOA18 A5B7, resolution 01 collection were derived using the Python CalculateSvp class from the objectively analysed temperature ( t_an ) and salinity ( s_an ) fields at the selected source grid cells and standard depths. Two separate estimates are produced: v_an_chen , calculated using the implemented Chen–Millero/UNESCO-type temperature–salinity–pressure polynomial, and v_an_leroy , calculated using the Leroy, Robinson and Goldsmith (2008) temperature–salinity–depth–latitude equation; both yield sound speed in metres per second. For the former, pressure is estimated from depth and latitude using Leroy and Parthiot (1998), with an optional configured regional correction, and converted from MPa to bar before evaluation. The class applies these calculations directly to the climatological inputs without additional spatial or vertical interpolation, extrapolation or missing-value filling. The results are derived climatological sound-speed estimates rather than direct acoustic measurements. The files in this dataset are used with these MB-System tools: mbsvpbest, mbsvproute, mbsvplocation, and mbsvpnearest. They are available here: https://github.com/dwcaress/MB-System References: https://www.ncei.noaa.gov/sites/default/files/2022-06/woa18documentation.pdf https://www.ncei.noaa.gov/access/world-ocean-atlas-2018/ https://www.ncei.noaa.gov/access/world-ocean-atlas-2023/