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interval. This convinces us that the EDR peak is not caused by random error of radar
measurements.
Fig. 13. EDR along the flight path estimated by the aircraft B777 (blue dots) at 13:05 UTC and
by the TDWR radar at the time indicated in the legend on 19 April 2008. X axis is the
distance between aircraft and the end of runway. The distance interval shaded by the green
color indicates where the aircraft passes through the altitude interval observed with the 0.6 o
elevated beam.
It raises another question: the aircraft may contaminate the radar measurements of the
atmospheric status, since the aircraft disturbs the atmosphere and changes the original
atmospheric condition in the measurement region as it flies by. In addition, aircraft itself as
a target embedded in other scatterers, such as raindrops, may contaminate the spectrum
width measurements as well. Both of the two factors could affect spectrum width and EDR
value.
It could also be seen that the radar EDR profiles do not match the two aircraft estimated
EDR peaks at the distance of 3.65 and 4.90 nm. It might be caused by the spatial difference
between the aircraft and the radar beams. The flight heights at the distance of 3.65 and 4.90
nm are higher than the radar beams by about 260 m and 400 m respectively.
Wind shear contribution to spectrum width measurement for this case has been examined.
After removing wind shear contribution, the EDR peak at the distance of 0.69 nm is reduced
from 0.48 to 0.46 2/3 ms (not shown) at 13:05 UTC. It means that wind shear contribution is
small in this region. Because wind shear of the large scale mean wind should be persistent
over the 4 minute for entire volume scan, the EDR peaks without wind shear contribution at
13:04 and 13:06 UTC at the distance of 0.69 nm are reduced to 0.67 and 0.74 2/3 ms
respectively. It indicates severe turbulence that is matched with aircraft estimate at 13:05
UTC.
Note that the aircraft estimated EDR is considered as ground truth in the above analysis, but
it also contains errors and requires significant QC effort, especially as airplane is climbing or
descending (Gilbert et al., 2004).
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