A.Their bearing is almost constant，even when the true bearing of the contact changes appreciably
B.They always appear on a bearing of 90°from the true bearing of the contact
C.The indirect echoes usually appear in shadow sectors
D.When plotted，their movements are usually abnormal
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A.radio signals reflect from a solid surface
B.sound waves travel at a constant speed through water
C.radar signals travel at a constant speed through water
D.pressure increases with depth
A.Water temperature
B.Climatology data
C.Speed of advance
D.Depth contours
A.Soundings
B.Waypoints
C.Meteorological data
D.Radar targets
A.Radar targets
B.ARPA vectors
C.Hydrographic data
D.All of the above
A.beam
B.radar
C.light beacon
D.reflector
最新試題
An ECDIS is required to display which information?（）
Deviation in a compass is caused by the（）.
The transmission time duration of a single pulse of radio-frequency energy is a function of the（）.
Compass error is equal to the（）.
A Doppler speed log indicates speed over ground（）.
Gyrocompass repeaters reproduce the indications of the master gyrocompass. They are（）.
Deviation is the angle between the（）.
（）should be used during the poor visibility if the radar’s screen shows heavy sea returns.
The minimum range at which a target can be detected is basically determined by which of the following?（）.
Compass deviation is caused by（）.