14193627 Radar Presentation 07

7/27/2019 14193627 Radar Presentation 07

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Picture orientation

Orientation is the choice of directional referens to be

represented by the 000 (12 oclock) graduation on the

fixed bearing scale around the CRT.


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1-ships head -up orientation (unstabilised)

-The observer views the picture with the heading marker

(and thus the ships head) at the top of the screen.

-There is no input of compass information to the display

-The objects on the starboard side of the ship will lie on the right and

those on the port side will lie on the left.

-Ships head -up orientation is corresponds directly with the scene as

viewed through the wheelhouse window.

-


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-At every change in the direction of the observing vessels heading,

the entire picture (apart from the heading marker), will rotate by an equal

but opposite angle. This characteristic limits the usefulness of the orientation

in three specific ways.

1-If a large alteration of course is made, any areas of land echoes are smeared

across the screen, making it difficult to identify specific features.

The afterglow created during the the alteration may obscure isolated fixed or

floating targets for some time after the vessel is steady on her own course .

2- Due to the effect of wind and sea, the ship will yaw about the correct

heading on a display using an unstabilized orientation, this superimposes an

angular wander on the movement of all targets. Which limits the ease and

speed with which bearings can be measured.

3-The disruption of the echo movement due to yaw limits the ease and

the speed with which an observer can plot the movement of targets for

collision avoidance purposes


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1.4.2 True - north- up orientation

(stabilised)In true - north- up orientation, the observer wievs the picture with northat the top of the screen.

-During course alteration, there is no rotation off the picture .

-There is no angular smearing which is associated with any change in heading.

-There is no masking of targets by afterglow generated during the alteration

of course.

-True bearings can be read off directly and quickly.

-It is sometimes uncomfortable to view a north up orientation particularly

when the vessel is on southerly courses


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Course up orientation (stabilised)In course up orientation the heading marker is aligned to

the 000 graduation on the fixed bearing scale at an instant

ar which the vessel is right on the chosen course. A north

marker is displayed at the edge of the screen.

It eliminates the angular wander of the picture due to

yaw,while maintaining the heading marker in a

substantially (though not exactly) ships head up

position.


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ships head -up orientation (unstabilised)


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True - north- up orientation (stabilised)


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Course up orientation (stabilised)


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Picture orientation compared


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Picture presentation:

The picture presentaion is used to indicate if the movement of

displayed echoes is shown with respect to

(a) the observing vessel

(b) the water, or

(c) the ground.


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The relative motion display presentation

-In relative motion presentation the origin of the display is stationary and

the movement of all targets is shown with respect to the observing vessel.

-Commonly the origin is is located at the center of the circular screen,

also off -centred relative motion presentations are available.

-The esential feature is that the origin is stationary and as a consequence

targets exhibit their motion relative to the observing vessel.


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The true motion presentation:-In true motion presentation the echo movement of all targets is rendered

independent of the motion of the observing vessel.

-This is achieved by causing the origin of the picture to track across the

screen in a direction and at a rate which correspond with the motion

of the observing vessel.

-Question:Should the observing vessels course and the speed be measured with

respect to the wateror with respect to the ground?


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If the course and speed through the water are selected,

the true motion presentation is said to be sea-stabilized.

True motion sea stabilized presentation:To produce a true motion, sea stabilized presentation the origin of

the picture must be made to track across the screen in a direction

and at a rate that correspond with the observing vessels course and

speed through the water.

True motion ground stabilized presentation.To create ground stabilized of atrue motion presentation, the origin of

the picture is made to move across the screen in a direction and at a rate

which correspond wi,th the observing vessels track over the ground.

To achieve this, the in put data must have a component which represents

the observing vessels course and speed through the water plus a further

component which represents the setand the rate of the tidal stream or current.


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The relative motion display presentation

A) CHART1


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2


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3


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True motion sea stabilized presentation:

1


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2


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3


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a) CHART

True motion ground stabilized presentation.

1


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2


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3


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Presentations: summary of features


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14193627 Radar Presentation 07

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Transcript of 14193627 Radar Presentation 07