Useful articles
AIS SAAB R4 installation on ships without MMSI / IMO
The automatic identification system SAAB R4 contains information about the vessel, which includes:
MMSI number
MMSI number
24.12.2013
Doppler speed logs
Doppler speed measuring log vessel the Doppler effect, which consists in that the signal emitted from a moving object taken fixed observer offset frequency wherein the offset frequency is proportional to the degree of speed of a moving object.
For the sake of clarity, we consider the measurement front to rear speed vessel.
The figure illustrates a system with a pair of beams.
Ultrasonic waves are radiated at an angle ? to the sea surface in the direction of movement of the ship in the opposite direction. If the speed of the vessel V, then the source of the ultrasonic wave (transmitter) approaches or retreats from the reflection point on the sea bottom at a speed Vcos?.
This relative movement causes d oplerovsky shift and ultrasonic waves reflected from the seabed and received by the transducer at frequencies F o + F Dand F o -F D . lag processor calculates the difference fo + F D and F o -F D to determine values only d oplerovskogo shift F D .
(F o + F D ) - (F o -F D ) = 2F D
Since, theoretically, F D can be defined as
F D = 2Vcos? XF o / C (C: Speed of sound in water), and F o , C and ? are known, then, with the known value of F D can calculate the speed V.