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 electronic depth finder operates on the principle that（）.
A Doppler log in the volume reverberation mode indicates（）.
（）20 targets can be tracked at one time．When maximum tracking capacity is reached，no further acquisitions are possible.
（）is on the panel of radar.
A radar range to a small，charted object such as a light will provide a line of position in which form?（）.
Error may be introduced into a magnetic compass by（）.
Deviation in a compass is caused by the（）.
A tall object with a light on or near the shore，to act as a guide or warning to mariners is called（）.
A barometer showing falling pressure indicates the approach of a（）.
The transmission time duration of a single pulse of radio-frequency energy is a function of the（）.