Handbook of Propagation Effects for Vehicular and ... - Courses

Attenuation Due to Roadside Trees: Mobile Case 3-19
3.5 Attenuation Effects of Foliage
3.5.1 K-Band Effects
Measurements made in Austin, Texas during February and May when the trees were
without and with leaves, respectively, enabled a “foliage’’ adjustment model to be
developed. The formulation relates equal probability attenuation (dB) corresponding to
“foliage” and “no-foliage” cases at K-Band and is given by
and where
A ( Foliage)
+
)
C
= a bA(
No Foliage
(3-15)
a = 0. 351
b = 68253 . , (3-16)
c = 05776 .
1 ≤ A( No Foliage)
≤ 15 dB and (3-17)
8 ≤ A( Foliage)
≤ 32 dB . (3-18)
This formulation was derived from “no-foliage” and “foliage” mobile measurements
made during February and May of 1994, respectively, in Austin, Texas during the ACTS
campaigns. The time-series signal level characteristics for these two cases are shown in
Figure 3-17 and Figure 3-18, where the measurements were made along a one kilometer
segment of a street heavily populated with Pecan trees. Shown are the minimum,
maximum, and average signal levels over one second periods for a sampling rate of
1 KHz. The corresponding cumulative fade distributions are shown in Figure 3-19 where
the dashed and solid curves correspond to the “no-foliage” and “foliage” cases. The
direction of travel for these runs was approximately orthogonal to the satellite pointing
direction. The optical blockage to the satellite during the full foliage period was
estimated to be well in excess of 55%. Performing a least square fit associated with equal
probability levels of the attenuation for the two curves in Figure 3-19, the formulation
(3-15) was derived. A comparison of the measured and predicted levels describing the
foliage versus no foliage fades is given in Figure 3-20. The predicted curve (dashed) is
shown to agree to within a fraction of a dB up to fades (with foliage) of approximately
38 dB.