How long should your time window be opened during a GPR (ground penetrating radar) survey?
I have seen don’t open up the time window enough and miss targets completely that could possibly have been detected. To counter this, I have seen some folks just go nuts and open it up as long as possible so they don’t miss any targets. The logic is “if I open it up as much as possible I never have to worry about missing anything.
There are three (3) problems with doing this however:
1. You have limited hard drive space and the longer you open up your time window, the more data (usually irrelevant data) is being stored on your hard drive. If you are remote this could become an issue, but most hard drives nowadays are large enough to handle it.
2. Data collection speeds will suffer because the longer the time window is open, the slower the GPR needs to move to collect data for that allotted time. If you move too fast, your GPR will probably yell (okay, beep, but someone should create one that yells) at you. If you are on a budgeted project, data collection speeds could slow down so much that projects could take twice or three times as long to collect.
3. The resolution of your data will suffer because the GPR uses a defined number of points (samples) to digitize each trace. If you open up your window, but use the same number of points to digitize, then your trace will not be accurate. You could increase the number of points used to digitize the trace but your run into problem number 2 again and you will have to move even more slowly.
Increasing your time window and increasing the samples can be helpful in detecting deeper targets that are usually outside the range of your antenna’s typical prospection depth, but this should be used only when needed.
So how long should your time-window be opened? Long enough to identify your expected target depths plus about 20 to 30 percent longer. This will allow for inconsistencies in velocity or inaccurate information on unexpected depths.
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