Magnetic Data Interpretation in a High Noise Urban Environment

• DOI: 10.4133/1.2922716
• Publication Date: 2009-05-14T17:30:54Z
• Authors: Jennifer Holt; Jeffrey Daniels
• Keywords: 11. Sustainability; 01 natural sciences; 0105 earth and related environmental sciences

Geophysics is increasingly being used in high noise urban environments, like Brownfields. Ground penetrating radar (GPR) or induction electromagnetic methods (EM) are the most widely used technique for site characterization in these settings since it is generally assumed that utilities and buildings make it difficult to obtain good magnetic measurements. However, recent tests at a Brownfields site in Chicago show magnetic methods can also be used in an urban environment. The vertical gradient of the magnetic field is most often used, but at this site the horizontal gradients added significant information to the interpretation. In addition, the three different gradient components show alternate trends of the anomalies. Many subsurface features, like pipes, run north-south or east-west in urban areas, and it is important to take measurement in each direction to improve the likelihood of finding such features. It is possible to combine the two horizontal gradient components to improve the interpretation by removing some of the bias introduced by running lines in a particular direction. Finally, there is the importance of contour scale. Different interpretations can be made with different contour intervals making the scale a very important part of the interpretation. Taking all this into account makes magnetic measurements a viable option in a high noise urban environment.