- This occurs when a ship uses separate transmitters for transmission of the sound pulse and reception of the echo.
- The transmitters are physically separated on either side of the keel or separated along the length of the keel.
- The depth measured at the E/S will be the slanted depth and not the direct below the keel depth.
- In deep waters, this error will not matter much but in shallow waters there will be considerable over reading which is dangerous.
Phased Ranges
- This is a technique to improve the quality of the echo displayed.
- The stylus does not begin its journey when the transmission occurs.
- The stylus starts moving after a delay which is introduced to match the depth of water to be measured.
- This ensures that the stylus is moving when the echo arrives at the E/S.
- For example, if it is intended to measure upto 200 meters of depth with stylus moving for 100 meter depth setting, the stylus begins to move after a time delay equivalent to and fro travel of sound upto 100 meters.
- Advantage of this method is that regardless of the depth of the water, the stylus is made to travel at the same speed meant of a lower depth which gives a clear and uncluttered picture.
- In Edrich Fernandese book, the Setting 1 is for 0-100m depth, Setting 2 is for 100m-200m depth and setting 3 is for 200-300m depth.
Why is Sound Propagation used in echo sounder?
- Sound propagation in water is used in marine navigation, as it is the only form of propagation, which could be, considered as efficient.
- Other forms, e.g. electromagnetic or light radiation attenuates rapidly and is of no use underwater
- Echo sounder, an aid to measure depth of water and Doppler log to measure speed are two sonar devices used in navigation.
