Notes on the Hodogram Applet

A hodogram displays a two-dimensional projection of a trajectory of a point moving in space. It is a crossplot of any two components of motion of the object. It is used in exploration seismology to find information on the direction travelled by a wave before it is detected at a receiver. The motion of the receiver itself is being plotted in the hodogram.

To use this applet you should first have four columns of ASCII data from a receiver. These should consist of three traces from, say, a 3-C geophone (for the same shot and receiver) and an accompanying time trace. The four columns may be in the same file or in separate files. Below is an example of an ASCII file with six columns. The relevant columns have been circled, with time in the fourth column and the vertical trace in the sixth column. The two horizontal traces are in other files not shown.

One easy way to copy-and-paste the data into the applet is to type Ctrl-a ("select all") in the ASCII file and then Ctrl-c ("copy"). The ASCII data will be scrolled to the end of the file and appear highlighted after the Ctrl-a action:

The applet webpage, when first opened, will appear like this:

Click inside the text area, then type Ctrl-a to select all the contents. The relevant part of the control panel will then appear like this:

Then type Ctrl-v ("paste") to transfer the copied data. The result looks like this:

Next check off the "Time" and "Vertical" boxes, as these indicate the data you are reading from this file:

Next change the column numbers to "4" and "6":

Right now there is a field a couple of lines down that reads "Data read in: none". After you click the "Read data" button, this changes to show the number of elements read in from each column.

Note that checkboxes have disappeared for "time" and "Vertical". It is no longer possible to read in data for these quantities unless you reload the applet. Two other checkboxes remain though. You should now repeat the steps above for other files to obtain the horizontal shear traces. The applet might then read as follows:

Finally click "Plot Hodograms". The left-hand side of the applet will appear as below:

Note the following:


Created by Chuck Ursenbach. First created May 18, 2007. Last updated November 16, 2007. Inquires should be sent to crewesinfo@crewes.org.

Copyright 2007, CREWES, University of Calgary