Spurious images arise in submarine periscopes under certain lighting and viewing conditions. Some of these unwanted images can occur as the periscope operator slews the LOS in elevation.
The rotational position of the head prism relative to the headwindow gives rise to various ray paths as shown in the ray diagrams below. Some of these conditions result in inter-surface reflections and internal reflections within the head prism. These give rise to ghost images and other spurious images of different types and sources.
These and other spurious images and causes of degraded periscope imagery are described in the accompanying presentation “Periscope Optical Anomalies”.