Appendix B: Exercises

Digital Imaging and Deconvolution: The ABCs of Seismic Exploration and Processing

Series	Geophysical References Series
Title	Digital Imaging and Deconvolution: The ABCs of Seismic Exploration and Processing
Author	Enders A. Robinson and Sven Treitel
Chapter	2
DOI	http://dx.doi.org/10.1190/1.9781560801610
ISBN	9781560801481
Store	SEG Online Store

1. Show that (in the case of two dimensions x, y) if the velocity is $v{\rm {=}}v_{0}{\rm {\ cosh\ }}\left(\tau y/r_{0}\right)$ then the rays are brought to a common focus (both time and distance) with common emergence distance $x{\rm {=}}r_{0}$ and common emergence time $t_{0}{\rm {=}}r_{0}/v_{0}$. This exercise represents the traditional case of diving waves.

2. In the case when velocity increases linearly with depth, we first found by integration that $x{\rm {=}}\rho \left(-{\rm {\ cos\ }}\theta {\rm {+\ cos\ }}{\theta }_{0}\right)$. Show that depth y can be found without integration by simply using Snell’s law in the velocity equation $v{\rm {=}}v_{0}{\rm {+}}ay$.

3. Let the velocity (in the case of two dimensions x,y) be $v(y)\ {\rm {=}}v_{0}{\rm {/}}{\sqrt {{\rm {1+}}ay}}$. Show that the equation for the raypath with initial angle ${\theta }_{0}$ to the vertical is

${\begin{aligned}ay{\rm {=}}{\left({\rm {\ cos\ }}{\theta }_{0}{\rm {+}}{\frac {ax}{\rm {2}}}{\rm {\ sin\ }}{\theta }_{0}\right)}^{\rm {2}}-{\rm {cos}}^{\rm {2}}{\theta }_{0},\end{aligned}}$

which is a parabola. Find the vertex of the parabola. Show that the ray is progressively bent toward the normal if a is positive and away from the normal if a is negative.

4. Let velocity (in the case of two dimensions x,y) be the exponential $v\left(y\right){\rm {=}}v_{\rm {0}}{\rm {\ exp\ }}\left(ay\right)$. Show that

${\begin{aligned}ax=2(\ arcsin\left(pv_{0}{\rm {\ exp\ }}\left(ay\right)-{\rm {\ arcsin\ }}\left(pv_{0}\right)\right)\end{aligned}}$

${\begin{aligned}at{\rm {=2}}p\left({\frac {\sqrt {{\rm {1}}-p^{\rm {2}}v_{0}^{\rm {2}}}}{pv_{0}}}\right).\end{aligned}}$

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Also in this chapter

• Reflection seismology
• Digital processing
• Signal enhancement
• Migration
• Interpretation
• Rays
• The unit tangent vector
• Traveltime
• The gradient
• The directional derivative
• The principle of least time
• The eikonal equation
• Snell’s law
• Ray equation
• Ray equation for velocity linear with depth
• Raypath for velocity linear with depth
• Traveltime for velocity linear with depth
• Point of maximum depth
• Wavefront for velocity linear with depth
• Two orthogonal sets of circles
• Migration in the case of constant velocity
• Implementation of migration

External links

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