As the exploration of the seafloor is extended ever further, automated classification and interpretation of sonar images are becoming increasingly important. However, many of the image processing techniques employed for these purposes consider the images simply as a collection of textures and neglect the process by which these images are formed. The most important aspect thus neglected is the directionality of the imaging process and its subsequent effect on the image textures produced. The paper reports the results of a systematic investigation of the effect of the sonar process on image texture directionality, illustrating the importance of the relative orientation of the sonar and the seabed features during the sonar image capture process. A frequency domain model is developed for examining and quantifying these orientation effects, and the subsequent effect on a classification system is demonstrated.