Exam 1 Flashcards
Doppler speed log
registers a change in frequency between the transmitted signal and the received signal and then calculates the velocity of the vessel based on the frequency shift
Echo sounding is a type of?
Sound Navigation and Ranging (SONAR)
Echo sounding is used to?
determine the depth of the water by transmitting sound pulses into water
Fathometer indicates the depth of water where?
under keel or where the transducer is located
Fathometer is dependent on both?
specular (direct) and diffuse (reflection at an angle) reflection
Range of fathometer is?
0 to 4,500 feet
Fathometers emit how many pulses per minute?
10 to 600 pulses per minute
Speed of sound through water is approximately?
4,800 feet per second
You should always know your _________s location.
Fathometer
What does a Oscillator do?
creates electrical signal at the desired frequency
What does a Transducer do?
converts electrical signal into ultrasonic vibrations for transmission. Also converts the return echo back into an electrical signal
Name two types of Transducers?
Electrostrictive and Magnetostrictive
types
It is essential the user select the _____ depth soundings on the depth sounder as the navigational chart in use.
SAME
Gain: the ____ the bottom, the less gain (sensitivity) required
harder
Define Bathymetric Navigation?
The method of navigating by using a fathometer
Speed Log is used to determine the vessels _____.
Velocity
Name three different Speed Logs?
- Patent logs: Small tubular finned device attached to the end of the drag line that would spin as the vessel moved through the water
- Pitot-static (pitometerlog): based on principle of comparative measurements between static and dynamic pressured in a pilot tube extending from a vessel’s hull
- Impeller log: electromagnetic device which used a small propeller spun by water which was then converted to an electrical signal
Modern Speed Logs are?
Electromagnetic or doppler
Define the Doppler Speed Log, Doppler Effect:
Shift in frequency between a transmitted and received signal caused by the motion of a vessel over bottom or through water
The Doppler Speed Log receives what through the water?
reflected signal from particles suspended in water.
True or False: The Doppler Speed Log registers change in frequency, not time, to measure speed
True
The speed of sound through ocean water is nearly always __________.
faster than the speed of calibration for the fathometer
Which factor has the greatest effect on the amount of gain required to obtain a fathometer reading?
Type of bottom
If a sound signal is emitted from the oscillator of a fathometer, and two seconds elapse before the returning signal is picked up, what depth of water is indicated?
824 fathoms
When operated over a muddy bottom, a fathometer may indicate __________.
two depth readings
The recording fathometer produces a graphic record of the __________.
depth underneath the keel against a time base
What should you apply to a fathometer reading to determine the depth of water?
Add the draft of the vessel.
When using an echo sounder in deep water, it is NOT unusual to __________.
receive a strong return at about 200 fathoms (366 meters) during the day, and one nearer the surface at night
All echo-sounders can measure the __________.
actual depth of water below keel
The speed of sound in water is approximately __________.
4.5 times its speed in air
A Doppler speed log indicates speed over ground __________.
in the bottom return mode
A Doppler speed log indicates speed through the water __________.
in the volume reverberation mode
What will NOT induce errors into a Doppler sonar log?
Increased draft
A Doppler log in the volume reverberation mode indicates __________.
speed through the water
A Doppler log in the bottom return mode indicates the __________.
speed over the ground
Velocity of sound through water to calculate depth of water?
(Depth = R * T)
The assumed speed of sound through water is approximately ______ feet per second or _____ greater than the speed of sound through air
4800, 4.5
Radar is an acronym for?
radio detecting and ranging
First commercial application on US merchant vessels occurred in the late _____.
1940’s
Define the Fundamentals of RADAR?
A transceiver sends a pulse modulated signal out, measures the time until the signal’s return, determines distance from this, and can display the returns in a directionally accurate presentation because of the use of a directional antenna
Radar waves are emitted on two different frequencies, what are they?
- X Band operates at 9,375 MHz with a wavelength of 3.2 centimeters
- S Band operates at 3,070 MHz with a wavelength of 10 centimeters
Define Superrefraction?
Superrefraction: increases downward bending of radar waves and therefore increases the ranges at which targets may be detected
Define Subrefraction?
Subrefraction: radar waves bend upward, thus the range at which targets can be detected is reduced
Define Ducting?
Ducting: extreme cases of superrefraction.
Sea Return is minimized by adjusting what?
RF GAIN or SEA CLUTTER CONTROL
Name the _____ interferences?
8
What are the different Radar interference’s?
Rain Clutter Indirect or false echoes Multiple Echoes Second-Trace Echoes Side Lobe Effects Electronic Interference Overhead Cable Effect Spoking (Equipment Failure)
True or False: Spoking is a Equipment Failure, Occurs when there is a modulator problem and indicated by many radial lines showing up on the radar screen
TRUE
The Fundamentals of RADAR!!!!!, THREE FACTS:
Uses basic time-rate-distance computations
Known speed of radar waves and time it takes for an echo to return
Radar waves travel at the speed of light
Watch Condition A?
One Deck Officer: Open Waters Clear Visibility
Watch Condition B?
Two Deck Officers: Entering or Leaving a Port Without the Pilot onboard
Watch Condition C?
Three Deck Officers: Situation where increased navigational assistance is needed, reduced visibility, higher traffic.
Watch Condition D?
Local Pilot Embarked
RULE 5
Look-Out
RULE 6
Safe Speed
RULE 7
Risk of Collision
Describe a Fathometer?
Determines depth of water by generating sonic pulses that are directed towards the ocean floor
The sonic pulses are reflected off the ocean floor and return to the transducer
