## Inversion concepts:  Introducing geophysical inversion

This chapter deals with basic concepts underlying geophysical inversion. Four sections provide an overview of essential ideas without mentioning mathematical details. Extensive use of flowcharts and figures should quickly introduce what inversion does, what is needed, and what can be expected for outcomes.

Note that the current chapter (Inversion Concepts) is conceptual in nature while Chapter 4 (Inversion Theory) covers the same ground in a more rigorous manner. It is recommended that the conceptual chapter be studied first before tackling the details provided in the theory chapter.

Inversion: Estimating models of physical property distributions based on geophysical survey data.

### Overview

 1a. Geophysical information can come directly from data. 1b. If models are needed, inversion must be applied.

Geophysical remote sensing data can be used to help solve practical environmental, engineering or exploration problems. In some cases, when only limited knowledge about the subsurface is required, inferences drawn directly from the data can be sufficient, as Figure 1a illustrates. This is a familiar linear framework in which data are gathered, then processed, plotted and interpreted.

However, when more detailed information about the subsurface is needed, quantitative models of the earth need to be estimated. This is geophysical inversion, as Figure 1b illustrates. Here the framework is not so simple. Data are used to constrain possible models of the earth, which have been estimated using some procedure suitable to the particular problem.

This short package does not explain details, but it should provide a conceptual understanding of what is involved when trying to solve the geophysical inverse problem.

NOTES about the last page: Section f. Inverting 2D DC data is challenging at this level. It assumes some understanding of DC resistivity surveying, and some experience with geophysical data. However, it does illustrate what's involved in carrying out inversion work. Readers with no more background than a good understanding of this "Inversion Concepts" chapter will gain a clearer impression of geophysical inversion by reading through the page carefully. There is a slightly more advanced version of this page at the end of Chapter 4 "Inversion Theory". If Chapter 4 is to be covered, you might gain more by deferring this page until then.