Chirp sonar data are processed using synthetic aperture processing to improve the spatial resolution and subsurface penetration of reflection profiles of the seabed. Synthetic aperture processing is implemented by calculating the vertical change in the positions of acoustic transducers between transmission and using the offsets to time shift the acoustic data so that reflectors are summed coherently. The changes in projector and hydrophone positions between successive transmissions are calculated based on Doppler velocity log and inertial measurement unit measurements of vehicle motion. The pulse repetition interval can exceed half‐wavelength spacing by increasing the number of physical hydrophone channels. Imagery generated from reflection profiles of seabeds generated in several depositional environments are compared, and used to quantify the improvement in the spatial resolution and the SNR of reflection profiles as a function of the length of the synthetic aperture.