Digital Analysis of Geophysical Signals and Waves/Digital Recording

George R. Jiracek

San Diego State University/Department of Geological Sciences

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Initial Publication Date: July 6, 2007

Summary

Sampling (digitizing) of geophysical data is explained using animations by multiplications in the time or space domains by Dirac combs and boxcar functions. Pitfalls in this process can render digital data totally worthless and/or completely misleading and must be avoided.

Exploration Methods, Gravity, Magnetism/Paleomag, Seismology | College Upper (15-16), Graduate/Professional

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Context

Audience

Used with NSF-sponsored research experiences for undergraduates (REUs), upper division course in geophysics field methods, and a upper division-graduate course in geophysical analysis. Designed for a geophysics course

Skills and concepts that students must have mastered

Undergraduate physics and mathematics through differential and integral calculus. A course in geophysics is desirable but not required.

How the activity is situated in the course

The Digital Analysis of Geophysical Signals and Waves (DAGSAW) web site is used as introductory material at SAGE (Summer of Applied Geophysical Experience) for REU students. It is also used in the sequence of material taught in geophysics field methods and geophysical analysis courses at San Diego State University.

Goals

Content/concepts goals for this activity

Understanding what the digitizing interval should be in space and time data, how long digital data should be recorded, and how fine the signal amplitude should be sampled.

Higher order thinking skills goals for this activity

Critical evaluation of properly digitized and truncated geophysical data in space and time domains.

Other skills goals for this activity

Report writing using actual geophysical data.

Description of the activity/assignment

Students use digitized ground magnetic data to visually and analytically learn the concepts of proper spatial sampling, frequency content in data, aliasing, and truncation (windowing). Addresses student fear of quantitative aspect and/or inadequate quantitative skills Addresses student misconceptions

Determining whether students have met the goals

Several years of using the attached 25-question quiz given before and after using the Digital Analysis of Geophysical Signals and Waves (DAGSAW) web site during a single morning session with undergraduate students has established an improvement of student test scores by an average of ~100%.

More information about assessment tools and techniques.