Title:
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Space-borne application of GNSS reflectometry for global sea state monitoring
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This research focuses on modelling the relationship between wind conditions, sea
roughness and GNSS reflections received from Low Earth Orbit (LEO). The motivation
for this study lies in the recent development of a GNSS reflections receiver platform for
the UK-DMC satellite and the numerous advantages proposed GNSS Reflectometry can
provide in Earth Observation and global disaster monitoring.
The fIrst part of the thesis focuses on the simulation procedure of received GPS-R
Delay-Doppler Map (DDM). Airborne GPS-R scatterometric model has been adapted
into this space-borne application research. Aft~r deriving DDM simulations according
to reflection scenario, the results of two-dimensional data-model fItting are presented
and analysed. The sensitivity discussion of current GPS-R model suggests some
limitations of the modelling method, especially under medium and high wind speed
ranges.
In the second part, we investigate the inversion scheme of DDMs for the purpose of
extracting a statistical wave model empirically. The similar model structure of DDM
simulation is used but the processing order is turned over. After deconvolution, DDMs
are inversed back to spatial energy maps and spatial slope probability maps. Three
inversion algorithms are developed and compared. Preliminary synthetic and real data
experiments give evidence of the feasibility of the inversion methodology.
Finally, in the third part of this research, a new geometric wave slope statistical model
is discussed in the context of wave fIeld simulations. The sensitivity of obtained
statistical model is discussed in terms of wind speed, wave direction and observing
incident angle. This provides an alternative view point to look into the wave slope
probability properties and compensate the traditional theoretic and empirical wave
modelling methods.
Key words: GNSS-Reflectometry, Delay-Doppler Map inversion, wind conditions, sea
surface roughness, slope probability density function, statistical wave slope model.
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