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Thesis - Leigh Moody.pdf - Bad Request - Cranfield University

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Chapter 4 / Target Tracking<br />

_ _<br />

4.12 Discussion<br />

Multiple-model (MM) filters are generally<br />

accepted as being more robust delivering<br />

substantially better performance than do single<br />

fixed or variable gain filters against<br />

manoeuvring targets. The early algorithms<br />

selected the best individual filter from a bank<br />

of filters. Later, more advanced algorithms<br />

combined the output from a bank of active<br />

filters according to the likelihood that they<br />

represent the true target dynamics. The IMM<br />

which is notable for its re-initialisation of<br />

filters in the filter bank, does not require a<br />

manoeuvre detector, and was selected for its<br />

simplicity and a performance that is equivalent<br />

to Bayesian filters with 2 hypothesis levels,<br />

Blom [B.9] .<br />

The tracking simulator hosts a conventional<br />

IMM whose filters are stimulated by reference<br />

or corrupted radar measurements and can be<br />

used either in isolation, or in combination.<br />

The IMM track is up-linked with missile plots,<br />

data time stamps and the updated IMM modal<br />

probabilities to the missile central processor.<br />

Here the tracks and plots are fused with IMU<br />

and seeker measurements to provide optimal<br />

data for missile guidance and stabilisation.<br />

Filters are provided for the most commonly<br />

encountered target motions, i.e. constant<br />

velocity, constant acceleration, high “g”<br />

turning (dog-leg) and weaves. As targets tend<br />

to manoeuvre for limited periods time,<br />

typically up to 5 s, earth referenced Cartesian<br />

position, velocity and acceleration states were<br />

selected rather than polar, or radar sight-line<br />

alternatives. For short-range tracking of agile<br />

targets it is better to retain the cross correlation<br />

that exists between the separated axes.<br />

A conventional EKF formulation was selected,<br />

even though for IMM application the tight<br />

control of system noise is paramount for<br />

discrimination purposes. A 10 Hz filter update<br />

rate was used for CLOS guidance, which is<br />

still high considering modern multi-purpose<br />

radar workloads. At this rate measurement<br />

4-26<br />

TARGET TRACKING<br />

SIMULATOR<br />

Read in user target tracking<br />

control data<br />

Read in user target tracking<br />

characterisation data<br />

I_IMM<br />

Compute tracking parameters<br />

TARGET<br />

SIMULATOR<br />

SENSOR<br />

SIMULATOR<br />

IMM_CONTROL<br />

IMM_MIXING<br />

( 10 Hz )<br />

Tracking filters and filter<br />

weight updates at 10Hz<br />

( VEL_FILTER )<br />

( ACC_FILTER )<br />

( MK1_FILTER )<br />

( MK2_FILTER )<br />

IMM Output /<br />

filter merging at 10Hz<br />

( IMM_OUTPUT )<br />

Target observer kinematics<br />

( FF_TG_GEOMETRY )<br />

Filter covariance monitoring<br />

( CV_CONTROL )<br />

( CV_STATS )<br />

Figure 4-7 : Target<br />

Tracking Simulator

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