ZZ Resistivity Imaging Pty. Ltd.
3.6 What is a roll-along survey? How does FlashRES perform a roll-along data collection?
A roll-along survey in resistivity exploration is a survey method to cover a long survey line with limited electrodes in each run. For example, the survey line in the figure below needs two runs to cover the survey line with a 64 electrode resistivity meter.
The number of overlapped points depends on the length of the survey line and expected exploration depth D. To get a reasonably good survey result, we suggest N >= 2*(D/dx+1), where D is the expected exploration depth and dx is the electrode spacing. But normally, we choose 16-electrode overlap or 32-electrode overlap, as shown below.
With FlashRES-UNIVERSAL, each run needs two 32-core cables. The two 32-core cables (Cable A and B) are laid as normally, as shown below. After the first run with these two cables is finished, Cable B, which has two connectors at both ends, is kept unmoved. While Cable A is moved to the other side of Cable B. Then the second run can be completed as shown below. This is how a roll-along survey with a 32 electrode overlap can be completed.
For a long roll-along survey with 16-electrode overlap. Also, we can provide four 16-core cables (Cable A, B, C, and D) for a roll-along survey with a 16-electrode overlap. For the first run, the cables are laid normally,as shown below. For the second run, only 3 cables (Cable A, B, and C) are moved to the other side of Cable D (which has two connectors at both ends) as shown below. Then the second run can then be done with the connection shown below. This is how a long roll-along survey can be easily finished.
After the first run of data collection is finished, the user needs to move cable A, B and C to the right side and leaves cable D unmoved for the second run as shown in the above diagram.