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The
Visibility Tool performs two calculations: (1) Object Discrimination
Analysis and (2) Line of Sight Angle of Incidence Analysis. The default
screen allows the user to manipulate basic visibility parameters to measure
the effect on an observer's ability to acquire a target. Advanced users may
select the "Advanced Input" located at the top right to manipulate
additional features.
Object
Discrimination Analysis:
After you entered your
values, click "Calculate" to run both analyses. On the upper right
quadrant, the Object Discrimination Analysis screen will display a graph
illustrating the probability of detection, recognition, and identification
of the selected target. To the left of the graph, a table displays the
threshold criteria for a Dodge Caravan target. Based on 195 current level
seven or greater airport traffic control towers, 1.5 standard deviations
below the mean, the minimum threshold for detection is 95.5%, recognition is
11.5%, and identification is 0.91%.
Refer
below for specific descriptions of the default screen parameters.
| Light Level (foot
lamberts - fL) - 1 fL = 3.426 candela per square meter |
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sunlight clouds: |
3001 |
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clear day: |
3000 |
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overcast day: |
300 |
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fairly bright moon: |
0.003 |
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moonless, clear night sky: |
0.0003 |
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moonless, overcast night sky: |
0.00003 |
| Ground Turbulence
(Index Structure Parameter - Cn2 m-2/3 @ 1
meter) |
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very weak turbulence: |
Cn2 <
6*10-16 m-2/3 |
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weak turbulence: |
6*10-16 m-2/3
< Cn2 < 6*10-15 m-2/3 |
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medium turbulence: |
6*10-15 m-2/3
< Cn2 < 6*10-14 m-2/3 |
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strong turbulence: |
6*10-14 m-2/3
< Cn2 < 6*10-13 m-2/3 |
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very strong turbulence: |
6*10-13 m-2/3
< Cn2
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| Perspectives Inputs |
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Tower Observation Height |
Observer eye height (above ground level in
feet) |
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Ground Elevation at Tower |
Elevation of ground at the base of the
tower (mean sea level in feet) |
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Ground Elevation at Key Point |
Elevation of ground at the designated key
point (mean sea level in feet). Key point is defined as the spot of the
surface of interest. |
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Corrected Observation Height |
Hc - (Ke - Te),
where Hc is the tower observation height, Ke is the
ground elevation of key point, Te is the ground elevation of tower. |
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Tower to Key Point Distance |
Distance between observer to key
point. The default screen allows feet or kilometers. |
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Target Acquisition Definitions |
| Detection |
is defined as the ability to notice the presence of an object on the
airport surface without regard to the class, type, or model (e.g., an object
such as an aircraft or vehicle). The observer knows something is present
but cannot recognize or identify the object.
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| Recognition |
is
defined as the ability to discriminate a class of objects (e.g., a class
of aircraft such as single engine general aviation aircraft). |
| Identification |
is defined as the ability to specify the
object (e.g., Dodge Caravan or Cessna 172) |
Line of
Sight (LOS) Angle of Incidence Analysis
defines the minimum line-of-sight slant angle required to perform airport
traffic control tower specialists' separation task.
After you entered your
values, click "Calculate" to run both analyses. The lower right
quadrant shows a table with a threshold value of 0.80 degrees. This
value represents the minimum line-of-sight angle of incidence for observer
viewing a key point. Below the table shows the needed height to meet
the minimum threshold.
LOS = ArcTan(Corrected
Observation Height/Tower to Key Point Distance)
Download
Results Document hyperlink is an
output file that lists all the default values with the two metrics.
The intended purpose of the output file is to archive the analyses.
Show Data/Debug
hyperlink allows the user to view the data that generated the object
discrimination graphs as well as other raw data calculations.
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