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

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Chapter 5 / Missile State Observer<br />

_ _<br />

T<br />

T<br />

( I − K ⋅ g ) ⋅ C ⋅ ( I − K ⋅ g ) + K ⋅ R K<br />

C : =<br />

⋅<br />

4-15<br />

Equation 4.4-29<br />

The stability of the Modified Gain EKF (MGEKF) and the provision of bias<br />

free estimates using bearings only measurements with non-Gaussian<br />

characteristics was studied by Song [S.14] . Since the range and range-rate<br />

measurements are not in the class of modifiable functions this technique is<br />

not suitable for this application.<br />

4.5 IMM Mode Conditioned Filters<br />

The dynamics of each filter in an IMM must be distinct, avoiding large<br />

injections of system noise making it difficult to distinguish between them,<br />

Stepaniak [S.11] . If filters of the same generic type are used their noise levels<br />

should differ by a factor of ≈10 so that they operate in distinct frequency<br />

bands, particularly when switching between manoeuvring and nonmanoeuvring<br />

models, Wheaton [W.2] . Filters with noise adaptation are<br />

unsuitable for the IMM application. The following target models were<br />

selected (identifying their parameters using the letter in parenthesis):<br />

• Constant velocity filter ( V )<br />

• Constant acceleration filter ( A )<br />

• 1 st order Gauss-Markov (Singer) filter ( S )<br />

• Weaving tuned target filter ( W )<br />

At long-range it is assumed that targets travel at constant speed interrupted<br />

by short bursts of acceleration. As the range reduces high acceleration<br />

avoidance manoeuvres can be expected. Apart from the 1 st order Gauss-<br />

Markov (Singer) filter the others use small amounts of system noise. The<br />

Singer filter is used to inject omni-directional noise system noise into the<br />

IMM to cope with changing target modes when its flight regime is<br />

uncertain, rather than target velocity directed noise. The Singer filters<br />

expressed in an Earth fixed frame are a poor representation of target<br />

dynamics compared with body directed acceleration models and its mode<br />

probability should fall once a new flight regime has been established.<br />

4.5.1 Constant Velocity Filter<br />

A non co-ordinated velocity model driven by noise in each Cartesian axis,<br />

V<br />

& P & : =<br />

The state transition and system noise matrices for each axis,<br />

iA<br />

t<br />

V<br />

w<br />

iA<br />

Equation 4.5-1

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