Kaplan Extended OS SST by the NCEP Optimal Interpolation (OI) Analysis from from LDEO/IRI Climate Data Library

For 1856-1981 this is the analysis of Kaplan et al. [1998]
which uses optimal estimation in the space of 80 empirical
orthogonal functions (EOFs) in order to interpolate ship
observations of the U.K. Met Office database [Parker
et al. 1994]. The data after 1981 represents the projection
of the NCEP OI analysis (which combines ship observations
with remote sensing data) by Reynolds and Smith [1994] on
the same set of 80 EOFs as used in Kaplan et al. [1998] in
order to provide enhanced data quality of the former in the
spatial resolution of the latter.

For more accessing the original NOAA/NCEP Reynolds OI SST data,
See: http://www.esrl.noaa.gov/psd/data/gridded/data.noaa.oisst.v2.html