Rapid parallel computation of optimised arrays for electrical imaging surveys [extended abstract]

Modern automatic multi-electrode survey instruments have made it possible to use non-traditional arrays
to maximise the subsurface resolution from electrical imaging surveys. One of the best methods for
generating optimised arrays is to select the array configurations that maximises the model resolution for a
homogeneous earth model. The Sherman-Morrison Rank-1 update is used to calculate the change in the
model resolution when a new array is added to a selected set of array configurations. This method had the
disadvantage that it required several hours of computer time. The algorithm was modified to calculate the
change in the model resolution rather than the entire resolution matrix. This reduces the computer time and
memory required and also the round-off errors. The matrix-vector multiplications for a single add-on array
were replaced with parallel matrix-matrix multiplications for 512 add-on arrays using the computer GPU
for the calculations. These changes reduced the computer time by more than two orders of magnitude. The
damped and smoothness-constrained least-squares formulations were used in the array optimisation model
resolution equation. The smoothness-constrained method can improve the model resolution for deep
extended structures where the resolution is poor.