Visibility Tool Help

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
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.
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.

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.

See And Avoid Tool Help

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.

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
Perspectives Inputs

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Oberver Eye Height Observer eye height (above ground level in feet)

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Observer┬áto┬áTarget Object Distance Distance between observer to Target Object.  The default screen allows feet or kilometers.
Target Object Inputs

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Front View SQRT(Wing Span * Height)

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Side View SQRT(Length * Height)
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.

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)

Download Results Documenthyperlink 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.