Subsurface Mapping with GIS
This article is dedicated to exploring the advantages of integrating Geographic Information Systems (GIS) into Geophysics. For all those who are not familiar with GIS, some basics concepts in this field have been included here as well as some useful links in references for all those who want to explore more the field of GIS.
Definition of GIS
GIS has become widely known and nowadays is used in many industries that have incorporated location as part of their daily business. To start with a definition of GIS, we can quote Dr. Roger Tomlinson, considered the “Father of GIS”. Mr. Tomlinson defines GIS in terms of its components that form part of a “model”. These components are Spatial Data, defined as data characterized for a geographic component that defines a specific location through the use of a coordinate system. This Spatial Data is stored in a Database where “it is available for software functions such as analysis and mapmaking”. Once this data is properly stored in a database is time to “identify the information products your organization needs” and here is where the information becomes dynamic and can be used as a technical tool to support the decision making process according to the user needs. At the heart of any successful GIS System are the people who get benefited of the interaction of all these components.
History of GIS
The Early History of GIS
“The field of geographic information systems (GIS) started in the 1960s as computers and early concepts of quantitative and computational geography emerged. Early GIS work included important research by the academic community. Later, the National Center for Geographic Information and Analysis, led by Michael Goodchild, formalized research on key geographic information science topics such as spatial analysis and visualization. These efforts fueled a quantitative revolution in the world of geographic science and laid the groundwork for GIS.”
GIS Past, Present and Future
“The history of GIS is composed of 3 historic stages:
- Pioneering and development
- GIS software commercialization
- User adoption
As time went on, GIS became a computer-based tool for storing and manipulating map-based land data. It’s now a multi-billion dollar industry responsible for some of the most important decisions our Earth is facing. What does the future holds for GIS? Real-time GIS? Virtual reality? Everyday, we are carrying the torch from the pioneers of GIS. We stand on the shoulders of giants. We are shaping the future of GIS. Companies, organizations and government adopt GIS because it’s a tool to help make knowledgeable decisions. Today, we barely scratched the surface on the history of GIS. Read more on its remarkable history.”
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Relation Between Geophysical Data and GIS
Geophysical data and geographic information systems (GIS) are tightly connected to each other. Data arising through geophysical endeavors involve earth science, mining, archaeology, seismic, hydrological, energy exploration, geology, marine and engineering. Many different kinds of sensors can be used to capture this kind of data. That information supports the development of 2D, 3D and 4D techniques related to spatial analysis, visualization and display. A large amount of geophysical work today is related to understanding earth processes relating to earthquakes, volcanoes and flooding – all involving geological and ground survey information. A basic question we ask when performing geophysical related surveys is “how can we understand earth processes better and what kind of information do we need to obtain to support improved knowledge?” If we understand earthquake activity is likely to arise, then we can develop strategies to mitigate events, should they happen to occur. This include deciding where to build infrastructure, what kinds of structures need to be built given the potential of expected events and other factors. In other cases understanding might mean gaining integral pieces of geological knowledge. Do specific kinds of geological formations mean that oil, gas or geothermal energy may be present? Clearly, geological knowledge and the data that supports underground understanding of geological formations is needed to support this kind of activity. Geodesy enables us to understand the earth’s gravitation, tides and polar motions. Other applications depending upon datums and coordinate systems can be seen as directly related to geophysics.
Applications of GIS in Geophysics
Integrating Geophysical Data in GIS for Geothermal Power Prospecting
“Geographic information system (GIS)–based resource assessment is an important and relatively inexpensive tool for identifying areas that are of interest for geothermal power production. Of particular interest is the under-exploited industry of co-produced fluids and low-temperature formation waters in oil- and gas-producing basins. Obtaining bottom-hole temperature (BHT) data is now free and easily accessible due to the efforts of the National Geothermal Data System (NGDS). Oil- and gas-producing sedimentary basins in Colorado, Illinois, Michigan, and North Dakota contain formation waters of a temperature that is adequate for geothermal power production (90–150 °C) using existing binary power plant technology. While resource assessment gives a broad picture of the energy available in a basin, the problem remains of knowing where a power plant must go, and if it is economically feasible to do so in any given area. The Denver, Illinois, Michigan, and Williston sedimentary basins were evaluated using a play fairway analysis methodology to identify optimum locations for geothermal power production. These regions have been previously assessed for thermal energy in place, and geothermal gradients from that study, along with gravity anomaly information, magnetic intensity, and digital elevation models (DEMs) for slope analysis were incorporated into a geodatabase for map generation. Raster layers were created and then reclassified into nine classes each, with high geothermal gradient, low magnetic intensity, low Bouger anomaly, and low slope receiving the highest values. The layers were then weighted using a matrix weight assignment similar to that used in the Environmental Protection Agency’s DRASTIC water pollution model, and combined with the “Raster Algebra” tool in ArcGIS. Areas of greatest potential were identified and overlaid on a DEM layer. This shows locations where temperature will be highest at the shallowest depths in regions of soft sediments, refining the map creation process.”
Process for Integrating Geophysical Data in Subsurface Mapping
This is a summary of the process to Integrate Geophysical Data into Subsurface Mapping as explained in the book Applied Subsurface Geological Mapping
Main steps are a cyclical process that involves in order: Data Validation, Data Interpretation, Data Extraction, Mapping and Review.
- Data Validation: Analysis of what seismic data represent. Do seismic data actually have some relationship to the geology in the subsurface?
- Data Interpretation: Validity of work rests on having an accurate and geologically correct interpretation of the seismic data, validating the data is the most important part of the process.
- Data Extraction: Extracting the information from the seismic data and transferring it onto the map so that it can be used effectively. Usually this process is referred to as posting and it represents the merger of the subsurface well log and the seismic information. Both types should be posted and used to construct the final interpretation.
- Mapping: The last step is the construction of the subsurface geologic maps. This step represents the culmination of all previous work, and in many instances it will be the result by which your work is measured.
Iterations of all these steps are necessary before a satisfactory subsurface map is completed.
- Roger Tomlinson. Retrieved from Wikipedia, the free encyclopedia: https://en.wikipedia.org/wiki/Roger_Tomlinson
- Roger, T. (2007). Thinking About GIS. Redlands California: ESRI Press.
- esri.com. What is GIS - History of GIS. Retrieved from ESRI: https://www.esri.com/en-us/what-is-gis/history-of-gis
- The Remarkable History of GIS. Retrieved from GIS Geography: https://gisgeography.com/history-of-gis/
- The Harvard Gazette. Retrieved from The Invention of GIS: https://news.harvard.edu/gazette/story/2011/10/the-invention-of-gis/
- Sensors & Systems. (n.d.). Retrieved from How do Geophysical Data and Geographic Information Systems GIS Relate to Each Other: http://sensorsandsystems.com/how-do-geophysical-data-and-geographic-information-systems-gis-relate-to-each-other/
- Crowell, A., & Gosnold, W. (n.d.). Geosphere. Retrieved from Geoscience World: https://pubs.geoscienceworld.org/gsa/geosphere/article/11/6/1651/132271/integrating-geophysical-data-in-gis-for-geothermal
- Tearpock, D. J., & Bischke, R. E. (2003). Applied Subsurface Geological Mapping. Upper Saddle River, New Jersey: Pearson Education.