%In the appendices I try to address several issues that I have
%mentioned briefly in this chapter, but  not adequately dealt
%with in the succeeding chapters.
%In Appendix~\ref{chap:nonlinear} I  show that doing a full line
%search rather than using conjugate gradient criteria isn't necessary
%because of regularization fitting goal.
%In Appendix~\ref{chap:param} I show how parameterizing our model
%in terms of splines can be effective, but relies on choosing the correct
%parameterization.  And finally in Appendix~\ref{chap:random} I show
%how we can produce error bars in our velocity estimate.
\par
One of the problems with most geophysics techniques is they provide only
a single answer and no measure of the uncertainty of the estimation.
In Appendix~\ref{chap:random}, I show how we can modify the way
we set up our inverse problem to obtain equi-probable results. By comparing
and contrasting these realizations we can better understand model variability
and uncertainty.
\par
In Appendix~\ref{chap:steer3d} and \ref{chap:op3d} I extend the concepts
introduced in Chapters~\ref{chap:tau} and \ref{chap:reg} to 3-D. 
Appendix~\ref{chap:steer3d} shows how a 3-D steering filter can be
constructed by cascading two 2-D filter. Finally, in
Appendix~\ref{chap:op3d}  I derive  a 3-D tau tomography operator.
