NorthStar 958 Operator's Manual page 197

Another important factor in the detectability of a radar echo is
the strength of the reflected wave. This strength will vary
depending on the type of material, size, shape, and height of
the target. Among the strong reflectors are bluffs facing the
ship, buildings, breakwaters, rock walls, and mountains. Some
of the weaker targets are wooden boats, sandy beaches, and
rubber lifeboats.
958 Operator's Manual, Rev. A Page 189