• GravCad is a 2D gravity modeling program. The lower window shows the geologic model, the upper window shows the gravitational response.
• MagCad is a 2D magnetic modeling program. The lower window shows the geologic model, the upper window shows the magnetic response. MagCad will calculate magnetic gradient as well as total field and allows for remanence as well as induced magnetization.
• Sounder is a 1D electrical resistivity modeling and inversion program for Wenner and Schlumberger arrays.
• 80toXYZ is a program we use to parse NOAA and DMA gravity data off of their CD ROM.
• Dig&Filt allows interactive visualization of Fourier transforms and many different filtering operations.
• Spliner can be used to demonstrate problems that develop with undersampling of data.

The following are MS-windows programs:

• GravCadW is an event-driven 2D gravity modeling program which includes nonlinear (Marquardt-Levenberg) inversion. You may need the full setup/install system but you might get by with just the .exe if you have the correct MS DLL libraries already installed. There are a few known bugs in GravCadW including:
  • The print routine will crash if you stack vertices (give them the same x-values).
  • Model/profile widths must be < 2^15 units wide.
  • Many features of the windows models are not saved when you save the models in the DOS format and I have not written the Windows save routines (yet...).
• PFdriver is a program that allows rapid conversion between 80toXYZ files, USGS potential field grids, and SURFER's file format.
• Invert demonstrates nonlinear regression/inversion for gravity data using a buried sphere. The user can choose to allow x, z, and/or density to change and step through iterations one by one.

The following are MathCad documents - again, no guarantees...

• Cooling Dike - quick and dirty solution of simple conductive cooling.
• Cooling Sill - quick and dirty solution of simple conductive cooling.
• Grav Inverse (.pdf)- demonstrates nonlinear least-squares inverse problems.
• Exponential error (.pdf)- shows pitfalls regarding, error analysis, of fitting lines in Log space.
• Vibroseis (.pdf)- shows how do think about (and calculate) synthetic seismograms using convolution and correlation in MathCad.
• Geotherm (.pdf) shows how to calculate a simple1D geotherm

And finally a few spreadsheets:

• Synseis demonstrates convolution with a spreadsheet and produces a simple synthetic seismogram to demonstrate the idea..
• 2Spheres shows the gravitational effect of moving two spheres progressively deeper into the subsurface - anomalies get broader and merge. This works well to help understanding of wavelength vs depth in potential field anomalies.
• FAA Density shows how to calculate the average density of local terrain using the Free Air Anomaly (FAA and topography) - a variant of Nettleton's technique.
• Schlum shows how to forward-model electrical sounding experiments for a Schlumberger array using convolution on a spreadsheet. The details are in: S.D. Sheriff, 1992, Spreadsheet modeling of electrical sounding experiments. Ground Water, v 30 #6, 971-974. Here's a draft of the manuscript.
• 3 point drill hole finds the dip vector from three {x, y, z} points. From there it calculates the apparent thickness of a bed pierced by a drill hole with given bearing and plunge. And it allows for determining the true thickness given the apparent thickness.
• Stereonet shows how to trick Excel into plotting directions on a stereonet.
• Hough presents the rudiments of the Hough transform for circles and lines.
• A quick demo of simple edge detection.

Notes and comments on lab CDs & software

Getting aeromagnetic data off the Former Soviet Union Aeromag CD

Some SURFER tips:
   Making Surfer maps with boundaries
   Making Surfer grid files using Excel
   Converting Surfer latitude, longitude grids for use with USGS potential field software