HIGH RESOLUTION GEOPHYSICS; WHAT IT MEANS AND WHAT IT CAN DO

Shallow geophysical methods for hydrogeologic studies have made significant advances over the last few decades and now provide much higher resolution images of the subsurface. This enhanced imaging capability provides much more useful information for a variety of hydrogeologic applications. This paper summarizes some of these advances in surface and borehole methods and creates a framework to illustrate how the methods described in the rest of the papers in this session can be used to answer a variety of questions.

The term high resolution is used to describe the imaging capability of the methods. While it is true that nothing has changed in terms of the propagation characteristics of the subsurface, advances in the sensitivity of the sensors and the noise levels of the recording systems have greatly enhanced the signal to noise ratio of the field data. Advances in microprocessors have allowed faster data sampling rates and multiple channel acquisition that have substantially increased the sampling density of many methods. Three dimensional surveys are becoming more common. Digital data acquisition and processing power have allowed data processing capabilities to improve dramatically. These advances have allowed more detailed images of the subsurface to be produced more quickly by a broader population of users under a broader range of field conditions.

This paper will present the basic concepts of sampling density and signal to noise ratio that control the sensitivity of common geophysical methods. The link between commonly measured geophysical properties and the hydrogeologic properties of interest to most studies will be discussed. Several examples of how the new acquisition and processing methods have improved subsurface imaging capabilities will be presented.