The previously reported [P. B. Nagy, J. Acoust. Soc. Am.93, 3224 (1993)] anomalous high‐frequency attenuation of slow wave transmission through air‐filled porous plates was further investigated by a novel experimental means. In order to investigate the heterogeneous nature of the pore structure, the experimental system was modified so that the spatial variation of the transmitted acoustic field could be measured by a sharply focused receiver. The experimental results indicate that the observed attenuation is mainly due to viscous losses. Owing to the a couple of simple technical modifications and improvements such as beam focusing, automated scanning, increased dynamic range, and greatly accelerated data acquisition, it became possible to use the slow wave transmission method as an ultrasonic imaging technique. This novel approach can be used to study the heterogeneous pore structure in permeable solids with a few‐millimeter‐resolution in the 100‐ to 500‐kHz frequency range.