In order to improve along track resolution and improve upon the range dependency of sidescan sonar, Synthetic Aperture Sonar (SAS) systems are being developed by several companies. These are being developed under defense contracts, but the potential for more efficient and accurate mapping of seafloor habitats is inherent.
A good background from ICES is here.
Another background from IEEE is here.
Applied Signal Technologies SAS (the image above is from this website)
Be a Wikipedia author--bad description of SAS!