“…The difference between our observed values, , and the estimated mappings, , in (10) is the observation error, , hence the index of performance we wish to minimize, , is defined as follows: (11) where remains the . The optimum value of for which the performance index, , attains its minimum value is obtained by solving the classic least squares relationship (12) where the correlation matrix is of size or , depending on the temporal model ( or -is the number of temporal harmonics, the number of spatial harmonics).…”