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

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Chapter 5 / Missile State Observer<br />

_ _<br />

The filter weights used are those prior to update by the measurement<br />

likelihood function. The 2 nd term accounts for the each filters deviation<br />

from the weighted mean. The weighted sum of the filter states and<br />

covariances after the measurement updates,<br />

IMM<br />

C<br />

+<br />

: =<br />

N<br />

∑<br />

i : = 1<br />

µ<br />

+<br />

i<br />

IMM<br />

⋅<br />

⎛<br />

⎜<br />

⎝<br />

X<br />

+<br />

C<br />

+<br />

i<br />

4-25<br />

+ + ( µ ⋅ X )<br />

=<br />

N<br />

∑<br />

i : = 1<br />

i i<br />

:<br />

+<br />

Equation 4.10-3<br />

+<br />

+ +<br />

+<br />

( X − X ) ⋅ ( X − X )<br />

i<br />

IMM<br />

i<br />

IMM<br />

T<br />

⎞<br />

⎟<br />

⎠<br />

Equation 4.10-4<br />

As well as up-linking missile measurements, the IMM target state and<br />

covariance (upper triangular partition) data, measurement reference time<br />

and filter probabilities are transmitted to the missile, the later providing a<br />

target manoeuvre indicator.<br />

4.11 Target Tracking Simulator<br />

The target-tracking simulator shown in Figure 4-7 contains the embedded<br />

target and sensor simulators. Initialisation and characterisation of the<br />

tracking function is performed in the normal fashion, although there is no<br />

dedicated default data for the tracking simulator. The target simulator is<br />

automatically activated inside the integration loop, providing the radar<br />

(sensor) with reference data.<br />

The tracking simulator is isolated by setting the program termination time to<br />

be less than the missile launch time (TIMEND < TLAUNCH). Either the<br />

radar or HMS sensors must be activated to obtain reference or corrupted<br />

measurement data. The selection of a single tracking filter, or the IMM,<br />

propagation and measurement update is controlled by IMM_CONTROL<br />

according to the bit pattern of IMM_TP:<br />

• Velocity filter VEL_FILTER ( bit 1 )<br />

• Acceleration filter ACC_FILTER ( bit 2 )<br />

• 1 st order Markov filter MK1_FILTER ( bit 3 )<br />

• Weave filter MK2_FILTER ( bit 4 )<br />

If a single tracking filter is selected IMM fusion is by-passed. When a<br />

combination of tracking filters are activated the IMM processes are<br />

automatically applied. The target observer states and covariances from a<br />

single filter or the IMM are processed to determine the parameters and<br />

expectations listed in §22.3 and §22.13 respectively.

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