<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="2298" name="inverse modeling" parent="713" scope="An iterative approach to estimate the form and characteristics of a physical system explained by observations or measurements. Frequently used to determine a subsurface geological structure from measurements of physical properties obtained at or near the earth's surface."/><uf><usefor name="geophysical inversion"/><usefor name="inverse problem"/><usefor name="inversion modeling"/></uf><bt><term thcode="2" code="713" name="mathematical modeling" parent="2285" scope="Operational representation of a system in which the characteristics and behaviors of the component processes, phenomena, or objects, understood using mathematical relationships, are represented by numerical values (measured or hypothetical), so that calculations carried out using them return numerical estimates of system parameters that were not measured directly."/><term thcode="2" code="2285" name="modeling" parent="734" scope="Human-constructed representation of processes, phenomena, or objects so that the behaviors, characteristics and relationships among things that are being studied can be understood without exhaustive data collection and analysis."/><term thcode="2" code="734" name="methods" parent="1" scope="Techniques, methods, procedures, or strategies for research, management, collection, or analysis of scientific information in USGS."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><rt><term thcode="2" code="2086" name="continuous resistivity profiling" parent="326" scope="Ship-based method of analyzing apparent resistivity of the sub-bottom (for example, spatial variation in pore-water salinity) by measuring the induced electromagnetic response to a current generated by the instruments."/><term thcode="2" code="326" name="electromagnetic surveying" parent="375" scope="Method of determining the shape and constituency of near-surface earth structures by variations of responses of the materials to electrical and magnetic fields. Use for ground-based methods of imaging."/><term thcode="2" code="459" name="geologic structure" parent="287" scope="General position of rocks in an area, and geometrical relationships among rocks."/><term thcode="2" code="470" name="geophysics" parent="291" scope="Branch of geology studying the physical characteristics and phenomena of the earth and its atmosphere."/><term thcode="2" code="501" name="gravitational field (earth)" parent="287" scope="Region or space around earth's mass which exerts a force that mutually attracts other masses in proportion to the product of the two masses and the distance between them."/><term thcode="2" code="677" name="magnetic field (earth)" parent="287" scope="The magnetic region surrounding earth.  It is generated by the dipolar characteristic of earth's core whereby earth itself acts as a great spherical magnet with poles near, but not exactly at, the North and South poles."/><term thcode="2" code="2085" name="magnetotelluric surveying" parent="326" scope="Passive geophysical technique that uses the earth's natural electromagnetic field to investigate the spatial variation of electrical resistivity in the subsurface."/></rt></descriptor>