Chapter 10, Section 10.5.2, Figure 10.15

Define a function that will be used to generate waves.

radout[a_,da_,amp_,θ_] := If[θ<0, a-amp*Sin[θ/da], a]

Generate the first wave.

p1 = 
Table[
N[{θ,radout[1.05+0.005, 0.01-0.0002, 0.012, θ]}],
{θ,0.1,-0.5,-0.001}];

Generate the second wave.

p2 = 
Table[
N[{θ,radout[1.05-0.005, 0.01+0.0002, 0.012, θ]}],
{θ,0.1,-0.5,-0.001}];

Generate the difference in radial distance between the waves.

p12 = 
Table[
N[{θ,
radout[1.05+0.005, 0.01-0.0002, 0.012, θ]-
radout[1.05-0.005, 0.01+0.0002, 0.012, θ]}],
{θ,0.1,-0.5,-0.001}];

Plot the first wave.

plot1=
ListPlot[p1,PlotJoined->True, 
AspectRatio->0.2, Axes->None]

Plot the second wave.

plot2=
ListPlot[p2,PlotJoined->True,
AspectRatio->0.2, Axes->None]

Show the two waves together on the same scale (see Fig.10.15a).

Show[plot1,plot2]

Show the difference plot.

plot12=
ListPlot[p12,PlotJoined->True,
AspectRatio->0.2,Axes->None]

Define a graphics object to represent the zero line.

zeroline = Graphics[Line[{{-0.5,0},{0.1,0}}]]

Show the difference plot and the zero line (see Fig.10.15b).

Show[plot12,zeroline]