Frequency domain analysis tools have been developed to analyse simultaneous multi-point measurements
of developed space plasma turbulence.
The Coherence Length technique enables the scale length for plasma wave structures to be measured
from magnetic field measurements. The coherence length defines a length scale for the measurement
of wave phenomena. Single satellite measurements can be used, the technique becoming
more reliable with higher numbers of satellites.
The technique is used to identify coherence lengths for waves observed in the magnetic field near
the bow shock by the dual AMPTE-UKSIAMPTE-IRM satellites, and for mirror wave structures
observed in the magnetic field in the magnetosheath by the dual ISEE-lIISEE-2 satellites.
The Transfer Function Estimation technique enables the transfer of energy between plasma
waves to be measured, from simultaneous dual-point measurements, resulting in linear growth /
damping rates and second-order wave coupling. The technique is improved by replacing the Least
Squares method for inversion with Regularisation.
The technique is applied to simultaneous magnetic field measurements near the bow shock by
the AMPTE-UKSIAMPTE-IRM satellites, where a linear instability in the wave field is identified,
which is attributed to an ion anisotropy instability, and accompanying sequence of second-order
three-wave coupling processes is also identified, which dissipates the energy from the linear instability.
The Wave vector Determination technique enables the identification of wave vectors from simultaneous
four-point measurements. The availability of four-point measurements means that the
reliance on Minimum Variance Analysis, and that of only being able to use magnetic field measurements,
is removed, the wave vector can be determined unambiguously directly from the magnetic
field measurements. The technique can identify between waves of different frequency, and waves at
the same frequency but propagating in different directions.
The technique is applied to simultaneous observations of the electric field by the four-point
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Cluster II satellites, enabling the determination of the wave vector and the identification of a mirror
mode structure, solely from the electric field measurements. Chapter 1 introduces the solar-terrestrial environment, briefly describing exploration of this environment
by man-made satellites and listing some aims of the analysis of data collected by the
satellites. Chapter 2 elaborates on what is meant by data analysis; Spectral Transforms are introduced
and described, with a comparison made between Fourier Transforms and Wavelet Transforms,
before a review is made of current data analysis techniques for satellite data. Chapter 3 defines and
focuses attention on the objectives of this thesis, which are addressed in the following three chapters.
Chapter 4 investigates the coherence length of plasma waves through use of the Wavelet Transform
and the Fourier Shift Theorem. Chapter 5 makes estimates of wave Transfer Functions, replacing
an established Least Squares inversion technique with a Regularisation inversion. Chapter 6 uses a
method to determine wave propagation directions, from multi-satellite data, that has not been applied
before due to the lack of availability of suitable data sets. Chapter 7 summarises the preceding
chapters. The Appendices contain reprints of papers resulting from, and relating to, this research.