<reponame>ruivalmeida/novathesis
%!TEX root = ../../template.tex


\section{Hypothesis}%
\label{sec:intro_hypothesis}

As stated in Section~\ref{sec:research_questions}, the main goal of my
work was to provide an answer to the question of how to design a
miniaturized tomographic atmosphere monitoring system, based on
\gls{DOAS}.  This sentence is the most important point of the project.
Every development from this point forward stems from it and is motivated
by it. It also requires some deconstruction in order to understand the
true scope of the matter. First, it is a miniaturized device. This means
that besides all the habitual requirements (performance, function,
adequacy, compatibility with the other components, safety and security)
in defining components in an engineering project, one must also keep in
mind the footprint of each component, and how much it weighs. Second, it
is a tomographic system, which means that not only the device must be
able to take line integrals from some kind of medium, it must also be
able to describe a predefined trajectory, with admissible levels of
geometric error, which complies to a certain projection geometry.
Otherwise, one would not be able to apply a tomographic reconstruction
routine to obtain the map of the target species concentrations. Finally
the system is supposed to monitor the atmosphere in some way. Now, as
implied in the same sentence, \gls{DOAS} is the technique that I am
trying to apply in this system. But as I point out in
Section~\ref{sub:doas} and with more depth in Section~\ref{sec:doas},
there are two families of \gls{DOAS}, and within them, many
sub-techniques. This system which I am developing is based on the
hypothesis that we can use an almost hybrid approach to \gls{DOAS}:
passive \gls{DOAS} instrumental simplicity and active \gls{DOAS}
retrieval simplicity. One could use a scattered sunlight measurement as
a light source for a \gls{DOAS} analysis, provided distances between the
two points are kept small, optical densities are low (clear atmosphere),
and both spectral measurements are taken in the same angle. With this
process, we would only effectively be using as projections the spectral
measurements of the \gls{ROI}. This hypothesis, while not being
mentioned in the library directly, has already been hinted at in several
papers, namely references~\cite{Frins2006, Casaballe2017,
Johansson2009}.
