Can the Self Trigger function (extra purchased option) replace the conventional trigger (hammer switch) and trigger extension cables typically used in refraction work?
Self-Triggering doesn’t provide sufficient timing accuracy to work for refraction surveys. For refraction interpretation, the accuracy of the absolute travel time between source event and arrival at the geophone must be on the order of ≤ 5 milliseconds. This cannot be achieved with the self-triggering processes.
This is because the self-triggering option works by breaking the data into small'Time Windows' and comparing the energy levels in these against the average background energy. These time windows and the ratio values are chosen by the user, so accuracy will depend upon the length of the window and how tightly you can specify the change in energy levels.
In cases where you don't have a trigger switch, you can set up the Geode to provide pre-trigger data and place a geophone close to the source. The extra geophone acts as a trigger and will start the survey at T = 0. For more information, click here