文档介绍：ASea bottom
BShip's speed
CSpeed of current
DWater temperature and density
[18]What often happens when using echo-sounder at river estuary where a layer of fresh water lies on the top of denser salt water?
AA scattering layer appears
BEcho sounder stops working
Cshallow water appears
DNothing abnormal happens
[19]Regarding the use of GPS, which one of the followings is incorrect?
AGPS is the most accurate global system today
BIts use is still under the US Department of Defence's control
CDGPS is more accurate than GPS
DGPS can provide a real-time position under any condition
[20]Without doubt the radar is a highly important navigation aid But duty officer shall aware that_____when using it
AIts range reading is more accurate than its bearing reading
BA low-lying coastline with a long, flat beach will show up properly on the radar
CRadar is only aimed at collision avoidance
DThe use of radar is necessary only when visibility is restricted
[21]As for racon,which one is incorrect in the following?
ARacon is a radar transponder
BRacon is often installed on major waypoints
CWhen activated by a radar signal, the Racon sends it back with an identifier
DRacon can be used to take place of radar
[22]What does a Racon help with?
AMeasuring the distance
BMeasuring the relative speed
CIdentifing a vessel
DIdentifing a seamark
[23]What does ECDIS stand for?
AE