Graphics Programs Reference
In-Depth Information
Moving Target Indicator (MTI)
and Clutter Mitigation
Chapter 7
7.1. Clutter Spectrum
The power spectrum of stationary clutter (zero Doppler) can be represented
by a delta function. However, clutter is not always stationary; it actually exhib-
its some Doppler frequency spread because of wind speed and motion of the
radar scanning antenna. In general, the clutter spectrum is concentrated around
and integer multiples of the radar PRF
=
0
, and may exhibit a small
f
f
r
amount of spreading.
The clutter power spectrum can be written as the sum of fixed (stationary)
and random (due to frequency spreading) components. For most cases, the ran-
dom component is Gaussian. If we denote the stationary-to-random power
ratio by
W
2
, then we can write the clutter spectrum as
)
2
W
2
δω()
(
ωω
0
σ
0
S
c
() σ
0
=
----------------
+
---------------------------------------
exp
-----------------------
(7.1)
W
2
2σ
2
1
+
W
2
2πσ
2
(
1
+
)
where
ω
0
=
2π
f
0
is the radar operating frequency in radians per second,
σ
ω
is the rms fr
e
quency spread component (determines the Doppler frequency
spread), and
σ
0
is the Weibull parameter.
The first term of the right-hand side of Eq. (7.1) represents the PSD for sta-
tionary clutter, while the second term accounts for the frequency spreading.
Nevertheless, since most of the clutter power is concentrated around zero Dop-
pler with some spreading (typically less than 100 Hz), it is customary to model
clutter using a Gaussian-shaped power spectrum (which is easier to analyze
than Eq. (7.1)). More precisely,
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