Continuous Transient Electromagnetic Sounding

The mapping of subsurface resistivity structures using transient electromagnetic soundings,<br>TEM, has gained an important role in hydrogeological investigations in Denmark. Regional<br>mapping with TEM have produced results, which leaves no doubt as to the ability of the<br>method to delineate freshwater sandy aquifers in well conducting hosts of Tertiary clays,<br>These results have been achieved measuring in a dense grid and do demonstrated the necessity<br>of estimating the data quality and variation by correlating adjecent data sets to reveal<br>distortion and multidimensionality of the measurements. The fact that these investigations are<br>often carried out in densely populated areas, where the cultural noise level is high, accentuates<br>this necessity even more (Christensen and Sorensen, 1994).<br>In this context a new method, the Pulled Array Transient Electromagnetic Method, PATEM,<br>is developed. The method applies a transmitter and a receiver coil system which are towed<br>along profile lines while measuring. With this method the cost of the field work is drastically<br>reduced. Furthermore, as the measurements are recorded very densely, adjacent data sets can<br>be correlated to ensure good data quality, and distortion from cultural effect from powerlines,<br>fences, etc. of the data sets is more easily revealed. Finally the necessary density of the data<br>sets for multidimensional interpretation can be provided (Auken, 1995).