Principle Of Measurement; Principle Of Measurement, Features - Furuno CI-80 Operator's Manual

PRINCIPLE OF MEASUREMENT, FEATURES

Planktonic layer
Ship's Speed

PRINCIPLE OF MEASUREMENT

When a moving vessel emits an acoustical pulse into the water
at an angle, a portion of emitted energy is reflected from the
seabed and other microscopic objects in the sound path, such
as plankton or air bubbles. The frequency of the received
signal is shifted from the transmitted frequency in proportion to
relative velocity between the vessel and underwater reflecting
objects. This is called Doppler Effect.
The CI-80 calculates and displays movements of ship and
currents at specific depths by measuring Doppler shifts
obtained from three separate directions.
Seabed
(Here, speed is a vector value including velocity and direction.)
Depending on the base of measurement, ship's speed is
expressed in two ways:
Ground tracking speed: Ship's speed and course relative to
(Absolute speed)
Water tracking speed:
(Relative speed)
Nav-aided speed:
(Absolute speed)
Frequency of reflected signal is
shifted in proportion to relative speed
between the vessel and reflecting
objects.
Figure 1
seabed (fixed base)
Ship's speed and course relative to
water layer just below the vessel
(floating base)
Ship's speed and course obtained
by external navigation equipment
(GPS)
1