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ences. Through sensitivity analysis models, the theoretical lower bound on
detectable differential target velocity as a function of the chaff cloud composi-
tion (e.g., clutter cross section, clutter spectral width, number of dipoles, and
clutter velocity standard deviation) and radar related parameters (e.g., wave-
form frequency, bandwidth, integration times, PRFs, and signal-to-clutter
ratio) are analyzed.
Overview
A five-step approach for detecting and tracking targets in highly cluttered
environments has been developed. The five steps are:
Utilize a 1 to 5 percent MB bandwidth, high PRF radar waveform, to mea-
sure the chaff cloud range extent, centroid, and velocity growth rate.
1.
Establish track on the centroid of the chaff cloud with the MB waveform.
2.
Based on course track information obtained in steps 1) and 2), implement
WB track (10% or greater bandwidth waveform) on the cloud centroid.
3.
Design a doppler bank of Moving Target Indicator (MTI) transversal filters
to provide adequate gain at specific velocity increments about the WB cen-
troid track.
4.
Process the Multiple MTI (M 2 ) doppler filters in parallel to detect differ-
ences in target Doppler (with respect to the cloud centroid track velocity).
Targets are detected when integration at the correct Doppler difference
occurs.
5.
Operational concerns that have been identified for implementation of this
approach include: (1) the ability of a radar to adequately track the centroid of
the chaff cloud (i.e., track precision); (2) the ability of a radar to detect small
differences in target Doppler relative to the chaff cloud centroid (i.e., Doppler
precision); and (3) the ability of a filter (in this case, a bank of MTI's) to
achieve the necessary processing gain to detect the target
Theoretical tracking accuracy of a chaff cloud
The single pulse thermal-noise error in a velocity tracking measurement
for optimum processing can be described by
σ f
1
1.81τ 2
σ f
=
--------------------------------------
(10.28)
×
SNR
where is the pulsewidth and is that for the target in track. To detect tar-
gets in clutter, substitute the difference-channel chaff-to-signal ratio for
τ
SNR
SNR
.
More precisely,
1
σ f
=
------------------------------------------------
(10.29)
1.81τ 2
×
C chaff
S
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