Page 92 - Radar Technology Encyclopedia

82 clutter (amplitude) distribution clutter filter

1 0.1

0.8
0.08 a = 1
Probability density 0.6 Probability density per dB 0.06

0.4

0.2 0.04 a = 2
a = 3
0 a = 4
1 0 1 2 3 4 5 6 0.02
a = 5
Power in units of mean power
Figure C21 Exponential distribution. 0 50 40 30 20 10 0 10 20 30 40 50

Power relative to median (dB)

Figure C24 Weibull distribution, plotted as density in dB.
0.7
d = 0
d d d
= 0
= 0
= 0
0.6 d =
s
x
0.4
d = 2 s
Probability density 0.4 d = 3 x 0.3 s y = 1 dB
x
0.5
s
0.3
0.2
0.1 Probability density per dB 0.2 s y = 3 dB s y = 2 dB
0 s y = 4 dB
1 0 1 2 3 4 5 6 0.1
Voltage in units of standard deviation
Figure C22 Rician distribution.
0
10 8 6 4 2 0 2 4 6 8 10
10 log s /s
m
2
Figure C25 Log-normal distribution. Median value = s .
m
1.8
The clutter (spatial) distribution describes the reflectivity
1.6 of clutter as a function of location, usually in range, azimuth,
m = 6
1.4 and elevation radar coordinates. In range, it may be limited by
m = 0 m = 5 the clutter horizon or (for surface clutter) by the interface
Probability density 0.8 m = 3 between land and sea. In azimuth it may depend on the hori-
1.2
m = 4
zontal extent of a cloud or on the land-sea interface. In eleva-
1
tion (at a given range) it depends on the maximum height of
sary part of the clutter model. DKB
0.6 m = 2 the precipitation or chaff cloud. These parameters are a neces-
m = 1
0.4 clutter equations (see RANGE EQUATION with clutter).
A clutter filter is a signal-processing element that is intended
0.2
to reject the frequency components of clutter while passing
0 target signals. Examples are the MTI canceler, the notch filter
0.5 0 0.5 1 1.5 2 2.5 3
in a range-gated MTI or pulsed doppler processor, and the
Power/Mean Power
response envelope of the filter bank in which filters contain-
ing clutter have been omitted or desensitized. DKB
Figure C23 Power of Rician distributed variable.
clutter fluctuations (see clutter spectrum).
Gaussian clutter (see clutter (amplitude) distribution).