A.Blind sectors
B.Sheltered area
C.Unseen area
D.Unscanable area
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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
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
最新試題
A barometer showing falling pressure indicates the approach of a（）.
An ECDIS is required to display which information?（）
The radar component that generates the radio-frequency energy in the form of short powerful pulses is which of the following?（）.
A FICTIVE LINE DISPLAYED ON THE RADAR SCREEN SEPARATING THE FAIRWAY FOR INBOUND AND OUTBOUND VESSELS SO THAT THEY CAN SAFELY PASS EACH OTHER defines（）.
Deviation is the angle between the（）.
A Doppler log in the bottom return mode indicates the（）.
（）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.
Compass error is equal to the（）.
An indirect radar echo is caused by a reflection of the main lobe of the radar beam off the observer’s vessel. Which of the following is NOT a characteristic of indirect echoes?（）.