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

Chapter 5 / Missile State Observer
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The intention is to further constrain the missile and target dynamics using
pseudo-measurements. Since these are not part of the filter propagation they
can be processed according to the dictates of loading and system
requirements. The “measurement” covariance reflects not only the inherent
uncertainty in each, but in the case of target dynamics it flight regime. This
is where the IMM filter uncertainties can be used to provide executive
control over the introduction of circular motion and GOT dynamics as
pseudo-measurements.
It is recognised that the EKF is operating in an environment for which it is
ill-suited. Highly non-linear dynamic and sensor measurements with
correlated errors violate the basic tenant of EKF design, namely Gaussian
statistics. It is a constant source of amazement that this type of filter works
as well as it does in such an environment. A list of measures that can be
taken to mitigate some of the more serious problems is provided from which
ensuring covariance symmetry is probably the most important in practical
applications.
Consider now some extensions to the work presented:
• The EKF does not respect quaternion normalisation that is performed after
each measurement update affecting the quaternion states. This process is
non-optimal and the covariances can be expanded to account for the error in
the process. An assessment of the error induced ignoring this correction is
needed, as covariance expansion is computationally intense if performed at
high frequency.
• A study into the up-link data rate that would avoid correlated target track
data so that this data can be treated as a measurement, simplifying both the
observer and reducing the up-link bandwidth.
• Whilst the equations relating to pseudo-measurement characterising the
observer state dynamics are provided, their systematic application has not
yet been considered. Rates, processing order, and links with the IMM filter
probabilities acting as manoeuvre detectors, all need to be explored and
benefits quantified.
• For air-launched applications, if the missile IMU sensors are of poor quality
the opportunity exists to estimate bias errors before launch, subject to
launcher rotation and vibration. The biases can be removed from the IMU
output leaving only residual and dynamically induced errors.
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