The UNESCO polynomial:
Fofonoff NP and Millard RC Jr, 1983. Algorithms for computation of
fundamental properties of seawater. UNESCO technical papers in marine
science, 44, 53 pp.
http://unesdoc.unesco.org/images/0005/000598/059832EB.pdf
Moritz H, 2000. Geodetic reference system 1980. Journal of Geodesy 74,
128-133.