Dialog when running delaytm.m

A number of GUI prompts require responses from the user. These are described as follows:

• Choose a G matrix file. Select G0003.mod, or perhaps your own edited version. Click OK
• Choose a D vector file. Select D0003.mod, or your own version. Click OK.
• Choose an E vector file. Select E0003.mod, or your own version. Click OK.
• Number of Shots? Enter 2 and click OK.
• Number of Channels? Enter 48 and click OK.
• Enter smoothness constraint. Enter a value of 0.1. What this does is increase the least squares error slightly, but adds a built in change to the objective function (the spatial derivative of the delay time solution). A value of zero here will produce the smallest error in the solution, but may map picking noise into false structure).
• The text window will show the shot delay times. They should agree with those specified in the constraint equations.
• The graphic window will have the refractor velocity in the title, and it should agree with the constraint applied in our problem. The plotted curve is a graph of the delay time solution, geophones.
• Enter overburden velocity. Here, type in a value of 664 as discussed above.
• The graphic will show a plot of the ground topography and the refractor structure. This is one end-limit solution that resolves the delay times completely as variations in the refractor structure. This is the preferred solution for this geologic setting.
• Enter a constant refractor depth. This is an alternative solution which resolves the delay times as variations in the overburden velocity (perhaps due to variations in water content). If you use the default, 10 m, you will see that the overburden velocity would have to vary from 1265 to 300 m/s to explain the data. This end-limit solution is not preferred in this geologic setting.
• Number of constraint equations? Enter 7 here, corresponding to the number of rows at the bottom of the G0003 file that we edited. This helps avoid a completely trashed plot where constraints become overprinted with the time plot. With more than one shot record, there may be some over plot of the computed times in this last graphic. You can fix that in Xfig.