| Factoring in the impact of natural terrain |
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When performing an airspace analysis, it can become necessary to
look beyond the results of the analysis summary reports to determine if the proposed
construction location is in fact “acceptable” or “not acceptable.”
Specifically, I am referring to the “hidden impact” Existing
Natural Terrain may have upon the results of the Airspace Analysis. Therefore,
we have introduced a new Slope Line tool to assist the Airspace user in determining
if and where the natural terrain impacts or “intersects” an aeronautical sloping
surface such as a 40:1 Departure surface.
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| Using the Airspace OMS's line slope tool |
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NOTE: The steps listed below describe the use of the Slope
Line tool; however, several assumptions have been made. The instructions below
assume that a topographic image has been loaded and calibrated as described in the
Airspace Survey manual, and that appropriate approach or departure trapezoid has been
overlaid upon the topographic image and the applicable study point has been plotted.
Should you need assistance with these steps, please refer to the Airspace
Survey manual contained on your Airspace Software CD in the “Manuals” folder for
detailed instructions.
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| How to Set-Up the Slope Line Tool |
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1. From the Menu Bar select the Draw Tab.
2. Then, select Line
3. Next, select Slope Line
4. When the Slope window opens, select the Slope Ratio from
the Drop down box as shown below. Note: The Slopes listed in the drop
down list box are standard items, however the user may also enter their own
value in the “slope” window. This example shows a slope of 40, which translates
into a slop of (40:1).
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5. Single click the left mouse
button on the [Screen] button in the
Slope window.
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6. Then, single click the left mouse button on the runway
end. The “Start Coordinates” will automatically populate the
“Lat:” and “Lon:” boxes in the Slope window as shown below.
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7. Next, the user may manually enter the “Start Coordinates”
elevation using the the computer keyboard if they have access to this elevation
data. If the user does not have the elevation data, it can be electronically
retrieved from a USGS server with a single click the left mouse button on the
caption “Elevation” in the Start Coordinates section of the Slope window. This will
allow the survey program to automatically retrieve the elevation of the point
selected in steps 5 & 6 above.
8. An elevation window will open displaying the USGS elevation
data for the Start Coordinates. Single click the left mouse button on the
[OK] button, and the Elevation field will automatically be populated with the USGS
elevation data.
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| How to Read the Slope Line Tool |
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9. Drag the cursor along the surface of the topographic map
stopping on a contour line within the departure trapezoid. For this example,
the cursor was stopped on the contour line 1000. Looking in the Range section
of the slope window, the Elevation indicated is the maximum allowable height AMSL at
the location where the cursor was placed.
Note: This “elevation” is automatically calculated based upon
slope selected and distance from start coordinates. Accordingly, this “elevation
value” changes as the cursor is moved across the surface of the topographic map.
For this Example… at the location marked with the Black + the max height
is 1006.47 feet AMSL.
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| How to Apply the Slope Line Tool |
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10. Repeat steps 5-9 until the areas where the ground meets or
exceeds the aeronautical surface being analyzed are identified and marked.
In this example what the Airspace analyst is looking for, by
using this tool, are places within the departure trapezoid where the natural terrain
exceeds the maximum allowable height indicated in the “Elevation” window of the
Range section of the Slope Line tool.
In other words, if the “elevation” displayed in the Range window
is less than the elevation displayed on the contour line for that point on the
topographic map, then the natural terrain penetrates the aeronautical surface.
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Each time an area of impact is identified, the analyst may click
the left mouse button and then select the [Mark] button on the right side of the
slope window. This will place an “X” at the location.
Once all the areas of impact are identified, the analyst can use
the Draw tools in Survey to “map out” the area of Existing Natural Terrain Impact
and provide this information to their engineering department or other internal or
external customers (see image below).
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