In past newsletters we have provided a variety of geophysical case study examples that Pyramid has completed over the years. These projects have showcased methods such as electrical resistivity, seismic testing, electromagnetics and ground penetrating radar that were used to investigate the subsurface. This month we wanted to focus on some of the supplemental tools and software that are used in conjunction with the geophysical equipment that allow Pyramid to assimilate the results and present all of the “pretty pictures” that come with geophysical reports.
The majority of our location maps and plan-view data presentations are shown on figures typically overlain on an aerial photograph. How do we collect the geophysical data in such a way that it can be overlain so precisely on an aerial? All of Pyramid’s geophysical investigations integrate Global Positioning System (GPS) data into the results. What exactly is GPS? “The Global Positioning System (GPS) is a U.S.-owned utility that provides users with positioning, navigation, and timing (PNT) services. This system consists of three segments: the space segment, the control segment, and the user segment. The U.S. Air Force develops, maintains, and operates the space and control segments.” Other countries also maintain their own satellites and control centers. The user segment is what you will see surveyors using in the field. It typically consists of a GPS antenna connected to a variety of data logger units.
For geophysics, Pyramid uses GPS in two ways. Some instruments allow the GPS information to stream directly into the geophysical dataset as it is being collected. These are typically our “moving” instruments, such as ground penetrating radar or electromagnetics, where the data is collected continuously as the geophysicist moves the instrument across a survey area. For stationary tests such as electrical resistivity or seismic methods, Pyramid will collect GPS points at the beginning and end of a transect, or at discreet data point locations. All of this allows us to locate the results on aerial photographs or in CADD software and share the location information electronically with our clients.
Once we have the data and the location information, how do we make the colorful figures that are typically associated with geophysical results? Some geophysical instruments also have their own processing software that generates some of the results we share, such as GPR. However, more often than not, we need to generate contour maps and other figures that show the results in unique ways using the data and GPS discussed above. One powerful piece of software that we use to do this is a mathematical gridding and contouring software package. This software helps combine data and generate contour maps using a variety of geophysical results. The software also utilizes Geographic Information System (GIS) tools that help to incorporate the GPS information we have collected. This allows us to calibrate aerial photographs to a particular coordinate system and present the contour maps on aerial photographs or overlay them onto a CADD drawing.
Pyramid also utilizes a 3D modeling program for some projects where the geophysical results can be combined and viewed in three dimensions. This approach can be very useful for applications such as cave and void detection, bedrock behavior, and general geologic mapping. Lastly, Pyramid utilizes multiple CADD software packages, most notably CADD software used by several state’s Department of Transportation (DOT) agencies. Pyramid can overlay our geophysical results on DOT roadway design plans to show where underground anomalies and objects such as buried storage tanks are located relative to a proposed road path, drainage features, or other infrastructure in the design plans.
As you can see, there are several steps and tools that are utilized beyond just the geophysical instruments that help us visualize the results and more accurately analyze the subsurface at a project site. The incorporation of GPS, along with various 2D and 3D modeling tools and CADD software, provide our clients with cutting edge maps and electronic files that help them identify hazards and understand the geology at their project sites.