Author: Amos Lawless
Software requirements: Matlab
George P. Cressman (1959) introduced an interpolation method which corrects the background gridpoint value (obtained from a forecast model) by a linear combination of residuals (corrections) between predicted and observed values. The residuals are weighted depending only upon the distance between the gridpoint and the observation. The scheme begins with a background field from a numerical forecast. The background value at each grid point is successively adjusted on the basis of nearby observations in a series of scans (usually four to six) through the data. The radius of influence (the size of the circle containing the observations which influence the correction) is reduced on successive scans in order to build smaller scale information into the analysis where data density supports it.
This program is a very simple implementation of a basic Cressman scheme, to illustrate how the scheme performs in areas of sparse and dense observations.
Reference: Cressman G. P., 1959: An operational objective analysis system. Mon. Wea. Rev., 87, 367-374.
The program source code, file cressman.m, can be found here and the documentation here (in pdf format).
