### Dipole-Dipole

 DIPOLE-DIPOLE PROFILING   This form of profiling does both profiling and sounding at the same time. With appropriate software, a two dimensional cross-section of the earth may be interpreted from the data. Therefore the dipole-dipole method is sometimes referred to as 2-D resistivitiy surveying. The current electrodes are placed at positions 1 and 2 and potential electrodes at positions 3 and 4. A resistivity observation is taken and then the potential electrodes moved to positions 4 and 5, etc. After finishing the profile with the current electrodes in positions 1 and 2, the current electrodes are moved to positions 2 and 3 and the process repeated.       Collection of the data, as well as inputting it to the computer is time consuming. Instrumentation is manufactured that includes cables with arrays of electrodes and a programmable resistivity meter with digital memory. Considerable time can be saved with such instrumentation. However, the cost of the automated instrumentation is about eight times greater than the MiniRes.  Appendix I has examples of field forms for collecting dipole-dipole data. L and R Instruments can assist you in obtaining software for the inversion of dipole-dipole data Apparent resistivity is                                          Ra     =   p R a n (n+1)(n+2)   Where R is the resistance measured by the MiniRes, a is the distance between adjacent electrode positions, and n is the number of internals between the nearest current electrode to its nearest potential electrode (C- and P+ in the example above). In the above figure C+ and C- are at electrode positions 1 and 2. The potential electrodes, P+ and P- are at positions 7 and 8. There are 5 intervals between the nearest current and nearest potential electrodes. In this case, the apparent resistivity becomes: Ra    =  p R a 5 (5+1)(5+2)  =  210  p R a   Following is a profile taken with MiniRes serial number 107: Super MiniRes serial number 107,  10 milliamps