Performs a local 2D-optimal interpolation (objective analysis).
Every elements in f corresponds to a data point (observation) at location x,y with the error variance var.
lenx and leny are correlation length in x-direction and y-direction respectively. m represents the number of influential points.
xi and yi are the data points where the field is interpolated. fi is the interpolated field and vari is its error variance.
The background field of the optimal interpolation is zero. For a different background field, the background field must be subtracted from the observation, the difference is mapped by OI onto the background grid and finally the background is added back to the interpolated field. The error variance of the background field is assumed to have a error variance of one.
Package: optiminterp