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
A Doppler log in the bottom return mode indicates the（）.
（）the canal transit，the radar was operating.
A radar display in which North is always at the top of the screen is a(n)（）.
A tall object with a light on or near the shore，to act as a guide or warning to mariners is called（）.
A deadhead is a(n)（）.
A radar contact will remain stationary on a relative motion radar display only when it is（）.
The microsecond unit of time is used in radar applications. The microsecond represents which of the following?（）.
（）20 targets can be tracked at one time．When maximum tracking capacity is reached，no further acquisitions are possible.
The radar component that generates the radio-frequency energy in the form of short powerful pulses is which of the following?（）.
Deviation in a compass is caused by the（）.