  Measurements of acoustic backscattering from glacially-eroded rock outcrops
were made off the coast of Sandefjord, Norway using a high-frequency synthetic
aperture sonar (SAS) system. A method by which scattering strength can be
estimated from data collected by a SAS system is detailed, as well as a method
to estimate an effective calibration parameter for the system. Scattering
strength measurements from very smooth areas of the rock outcrops agree with
predictions from both the small-slope approximation and perturbation theory,
and range between -33 and -26 dB at 20$^\circ$ grazing angle. Scattering
strength measurements from very rough areas of the rock outcrops agree with the
sine-squared shape of the empirical Lambertian model and fall between -30 and
-20 dB at 20$^\circ$ grazing angle. Both perturbation theory and the
small-slope approximation are expected to be inaccurate for the very rough
area, and overestimate scattering strength by 8 dB or more for all measurements
of very rough surfaces. Supporting characterization of the environment was
performed in the form of geoacoustic and roughness parameter estimates.
