  A method of interpolating the acoustic transfer function (ATF) between
regions that takes into account both the physical properties of the ATF and the
directionality of region configurations is proposed. Most spatial ATF
interpolation methods are limited to estimation in the region of receivers. A
kernel method for region-to-region ATF interpolation makes it possible to
estimate the ATFs for both source and receiver regions from a discrete set of
ATF measurements. We newly formulate the reproducing kernel Hilbert space and
associated kernel function incorporating directional weight to enhance the
interpolation accuracy. We also investigate hyperparameter optimization methods
for this kernel function. Numerical experiments indicate that the proposed
method outperforms the method without the use of directional weighting.
