Fundamental limitations of wave-front analysis by least squares

This paper shows that the problems of mode resolution in vertical-angle measurement with the existing serial array are due to absolute limitations in least-squares solutions, and not to deficiencies in the extraction methods. A geometrical approach introducing the idea of `effective dimensionality¿¿ is used. This gives a clear understanding of the nature of the obstacle, and has led to a simple display of the resolvability of various sets of modes. This insight indicates the nature of improvements required and could provide a valuable analytic basis for evaluating other aerial systems. It is suggested that information obtained from other criteria, such as correlation of vector amplitudes or differences in Doppler shifts can be used to supplement the least-squares results.