Application of small loops in near surface TEM surveys

2017-02-16T04:51:57Z (GMT) by Kruse, Anders
Transient Electromagnetic (TEM) surveys have improved significantly over the past 30 years and are now being applied to applications as diverse as ground water surveys and identifying unexploded ordinances. Recent improvements have focussed on reducing the shut off time to enable earlier time readings and greater resolution in the near surface. This project explored the possibility of additional improvements by reducing loop sizes further and managing resultant kickback issues through the use of components in the configuration, such as resistors. The aim was to reduce loop sizes while still being able to create quality surface plots and Conductivity vs. Depth Images (CDI). I explored ways of reducing the early time response through analysis conducted using LT Spice, and then tested the results through a series of experiments. I surveyed a Sandringham park with a small mobile TEM instrument with small loops (triangular loops with 3m sides) and conducted a magnetic survey. The park had previously undergone magnetic and TEM surveying, and was known to be contaminated with subsurface objects. I then did a full survey with the same instrument with 2.5x2.5m loops, optimised according to the results from testing undertaken. Finally, the results of the optimised survey were compared to the magnetic survey to validate the results, and previous TEM surveys to determine if the optimisations succeeded in their aim. Comparing the results of the survey using 2.5 x 2.5m loops with those of past site surveys showed that dampening components reduced noise to a manageable level and enabled an accurate surface plot. Analysis of the two TEM surveys taken using the same equipment at Sandringham Park demonstrated the improvements available through managing the electrical current with components. Improvements were also made to the ability to create CDI, however the images created were still incomplete.