In extreme environments with limited visibility, optical sensors have limited performance. The acoustic sensors can be one of the alternatives to the optical sensors in a low-visibility environment. However, the acoustic sensors have poor SNR characteristics, low-resolution problems, and loss of height information. Therefore, a proper signal processing technique is required. This research is a 3-D seafloor scanning method using multibeam sonar. It provides a unique analysis of sonar image geometry for extracting missing elevation information and can be continuously executed regardless of the existence of features.