  In this paper, we address the challenging problem of data association for
underwater SLAM through a novel method for sonar image correspondence using
learned features. We introduce SONIC (SONar Image Correspondence), a
pose-supervised network designed to yield robust feature correspondence capable
of withstanding viewpoint variations. The inherent complexity of the underwater
environment stems from the dynamic and frequently limited visibility
conditions, restricting vision to a few meters of often featureless expanses.
This makes camera-based systems suboptimal in most open water application
scenarios. Consequently, multibeam imaging sonars emerge as the preferred
choice for perception sensors. However, they too are not without their
limitations. While imaging sonars offer superior long-range visibility compared
to cameras, their measurements can appear different from varying viewpoints.
This inherent variability presents formidable challenges in data association,
particularly for feature-based methods. Our method demonstrates significantly
better performance in generating correspondences for sonar images which will
pave the way for more accurate loop closure constraints and sonar-based place
recognition. Code as well as simulated and real-world datasets will be made
public to facilitate further development in the field.
