Estimation of far‐field pressures from geometric near‐field measurements

Measurements of radiated noise are often made in the geometric near field of a cylindrical radiator to take advantage of high signal‐to‐noise ratios. At these ranges the far‐field beam patterns are not fully established and the corresponding sound pressure levels cannot be determined via a simple range correction. In this paper, three methods of estimating the far field given measurements primarily made in a horizontal plane are presented. All three methods employ propagator matrices to relate surface field quantities to the near‐ and far‐field pressures. The pressures measured over a segment of the receive array are multiplied by a weighting vector determined from the propagator matrices to minimize the mean square error between the actual and estimated far field. One method represents the surface field as a distribution of monopole sources of unknown strength. This method also employs an image source field representation to attenuate surface bounce contributions. The second method represents the surface...