DO YOUR OWN PRELIMINARY ANALYSIS
You can do your own anonymous
analysis of your proposed project’s impact on the NEXRAD radar network by using
the new NEXRAD Tool on the FAA’s Obstruction Evaluation (OE/AAA) web site
(DoD Preliminary Screening Tool)
Interpretation of the New FAA OE/AAA DoD Preliminary Screen Tool Results
EXAMPLE OF NEXRAD TOOL ON FAA's OE/AAA WEB SITE
Radar Line of Sight Graphs
The WSR-88D radar performs 360º scans of the atmosphere with elevation angles
between 0.5º and 19.5º. The WSR-88D samples up to 14 different elevations angles
for each complete scan of the atmosphere. The radar beam increases in height and
in diameter as it moves away from the radar, with most of the beams energy at
the beam center height. The bottom and top heights of the beam are defined as
the points where there is a 50% reduction in the transmitted energy. Below
the beam bottom height and above the beam top height the energy drastically
decreases. The area between the beam bottom and beam top is referred to as
the “beam”. There is reduced impact on the radar if the rotating blades are
below the beam bottom, especially at “close” distances.
Any object within the beam reflects energy back to the radar. The WSR-88D uses a complex
algorithm, called a clutter filter, to perform an analysis on the data to determine if
the returned energy is from a desirable target (weather) or not (non-weather clutter). One
factor used in the clutter filter process is the motion of the return. Clutter mitigation
filters within the WSR-88D can not filter rotating wind turbines due to the motion of the
blades. When the turbines are close to the radar, they penetrate more of the beam increasing
the amount of energy returned to the radar, resulting in higher reflectivity values, potentially
at multiple elevation angles.
Click here for a table with the 9 lowest scanning elevation angles and their associated
height in meters above the radar feed horn height, or click here for a visual
representation of the tables.
Note: The heights are above the radar feed horn for a
Standard Atmosphere. The range of the radar is greater than that listed in the tables and graphs.