It is often required to have accurate information on the sound absorptive characteristics of materials - reflection coefficient or absorption coefficient - in terms of angle of incidence. As one could anticipate, however the measurement of sound absorptive characteristics in terms of angle of incidence requires an apparatus of which can generate plane waves in all possible or desired angles of incidence. This rather practically infeasible requirement can be easily implemented by simply realizing that the spatial Fourier transform essentially decomposes a sound field into infinite number of plane waves. In other words, one could use any sound source to generate plane waves; the measurement system is not affected by the characteristics of sources. In this thesis, we propose a method of which estimate the reflection coefficient with regard to angle of incidence. A pair of line array is used for the measurement. The effect of window on the measurement is also studid. This is recognized very crucial to practically utilize the proposed method since it determines the loss of sound energy due to the finite dimension of measurement system. The effect of various measurement parameters such as the microphone spacing, the aperture size, and the spacing between measurement lines with respect to angle of incidence as well as wave length of interest on the estimation of reflection coefficient is treated in depth. It is also formulated and approved that the errors associated with the measurement system is to be minimized by employing the spatial LMS (Least Mean Square) method. A new measurement system is also proposed from recognizing that one can not use the infinite size material in practice; the practical size of a material is not very large enough compared with wavelengh of interest. Numerical and experimental results demonstrate the applicability of the proposed method.
