12.2.1 Surface fitting  12. Four-Dimensional Data Assimilation  12.1 Introduction

12.2 Commonly Used Analysis Techniques from 1950 to the late 1980s

Three major objective analysis techniques are presented in this section:

• Surface fitting methods. A mathematical surface (two-dimensional function) that fits irregularly spaced observations is determined in the region of interest. From the function defining the mathematical surface, one can then compute values of the parameters at gridpoints (where observations are not available).
• Empirical linear interpolation of observed values to grid points
• Statistical objective analysis - a method for estimating meteorological parameters at grid points, in which correlations among the analyzed variables determine the weights applied to the observations