Description and Evaluation of GDEM-V 3.0

Abstract

The GDEM (Generalized Digital Environment Model) has served as the U.S. Navy's global gridded ocean temperature and salinity climatology since its development began in 1975. This memorandum introduces a new version of this climatology, named GDEM-V 3.0, and discusses the techniques used in its construction. Several comparisons are shown between version 3.0 and the previous version (2.6) of GDEM to demonstrate several significant improvements. The largest change in methodology was to discontinue fitting temperature profiles to a prescribed nonlinear function and replace it by a method that horizontally interpolates temperature or salinity values separately at each depth level. In addition, the horizontal interpolation has been redesigned to avoid averaging dissimilar profiles separated by land boundaries. The vertical gradients of averaged profiles have been improved, particularly in shallow water, by application of a gradient correction algorithm based upon statistics derived from the profile data set.