JRC JMA-2343, Instruction Manual

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4.2 Returns from a Target
The intensity of returns from a target is related not only to the size of the target but
also to the materials and shape of the components making up the target. Accordingly,
larger objects do not necessarily develop strong returns.
On coastlines, in particular, the intensity of returns is dependent on their
physiographic features. For a coastline with a fairly gradual ascent, only inland
mountains areas may be displayed as echoes. This fact needs to be kept in mind when
measuring the distance to a coastline.
Since the echo which returns from a coastline with a fairly gradual ascent is weak,
observation of such land may not be able to be performed.
4.3 Propagation Path of Radio Waves
Radio waves may be shielded if there is a large intercepting obstacle (e.g.,
mountains, rain, snow, etc.) in their propagation path and any targets behind the
obstacle cannot be observed.
An island that is not displayed because of heavy
rain in between the own ship and the island
A ship that is not displayed because of an island
in between the own ship and the target ship