RRI: Rapid Relaxation Inversion

There is a bug in the implementation of frozen profiles(fictitious sites beneath which the model is held fixed at its starting value). This feature works properly ONLY if the frozen profile lies WITHIN the sites with actual data. Thus you cannot, at present, freeze the model outside of the data. This will be fixed in the next release. If this is a critical problem for anyone, I will explain how to fix it yourself.

The paper: Rapid Two-Dimensional Inversion of COPROD2 Data, Wu, N, Booker, J.R. and Smith, J.T., J. Geomag. Geoelec., 45, 1073-1087, 1993. describes useful strategies for inverting for static shifts using inv2d. If you simply set all the shifts free, you are likely to converge to a local minimum of the object function in which the resistivity data are well-fit, but the phase data are ignored. The basic idea behind all strategies that we have found useful is to weight phase data more strongly until their misfit is small and then bring in the resistivity.

NOTE: This problem noted in last section can often be reduced by damping the inversion for static shifts (see new release notes below).

NOTE:The following comment CONTRADICTS a statement made in file READ_ME supplied with inv2d.

When trying to fit TM mode data alone, experience has shown that varying the parameter that controls the depth-dependence of the norm ("eta") with iteration number can be very useful. For instance setting eta to 0.0 for the first iteration and letting it increase to 1.0 or 1.5 has the effect of forcing inv2d to fit the data with very shallow structure first and incorporating deeper structure only when shallow structure cannot do the job.

A new release of inv2d is planned for early 1995. It will have significant advantages over the current version:

  1. Discontinuties at which the model smoothness condition is suspended can be declared anywhere in the model. This is very useful for incorporating geological information, such as independently determined depth to conductive or resistive basement, mapped faults, etc.
  2. Individual model nodes can be frozen at their starting value. This is again useful for incorporating a priori information or testing hypotheses.
  3. Inversion of static shift coefficients can be damped. This is useful when you want the statics to change only if the data cannot be fit without changing the statics.
  4. Pseudo (or virtual) sites can be declared. These are sites at which an inversion is performed, but there is no measured data. They allow model freedom between sites with data. Normally, the model will simply be smoothed into such a site from adjacent sites. However, sometimes model changes beneath a pseudo-site can improve data fit at other sites. With no pseudo-site, the routine which interpolates structure between data sites would not allow such structure to exist.
  5. Outputs surface magnetic and electric fields as well as MT data.
  6. Outputs file containing the fields inside the model. These can be used to restart the inversion for further iterations. They will greatly speed up the first iteration of the restart and in most cases, will permit using 32 bit rather than 64 bit arithmetic for the inversion. This will halve memory usage and substantially improve speed on many machines.
  7. Versions for 486, Pentium, PowerPC and Mac machines as well as Unix workstations. Features that are in testing. Some may make it into the next release.
  8. Inversion of vertical to horizontal magnetic field transfer function data (sometimes called "tipper" by those trying to confuse people).
  9. Surface topography. This will include both the air-earth interface and the seafloor.
    1. Discontinuties at which the model smoothness condition is suspended can be declared anywhere in the model. This is very useful for incorporating geological information, such as independently determined depth to conductive or resistive basement, mapped faults, etc.
    2. Individual model nodes can be frozen at their starting value. This is again useful for incorporating a priori information or testing hypotheses.
    3. Inversion of static shift coefficients can be damped. This is useful when you want the statics to change only if the data cannot be fit without changing the statics.
    4. Pseudo (or virtual) sites can be declared. These are sites at which an inversion is performed, but there is no measured data. They allow model freedom between sites with data. Normally, the model will simply be smoothed into such a site from adjacent sites. However, sometimes model changes beneath a pseudo-site can improve data fit at other sites. With no pseudo-site, the routine which interpolates structure between data sites would not allow such structure to exist.
    5. Outputs surface magnetic and electric fields as well as MT data.
    6. Outputs file containing the fields inside the model. These can be used to restart the inversion for further iterations. They will greatly speed up the first iteration of the restart and in most cases, will permit using 32 bit rather than 64 bit arithmetic for the inversion. This will halve memory usage and substantially improve speed on many machines.
    7. Versions for 486, Pentium, PowerPC and Mac machines as well as Unix workstations. Features that are in testing. Some may make it into the next release.
    8. Inversion of vertical to horizontal magnetic field transfer function data (sometimes called "tipper" by those trying to confuse people).
    9. Surface topography. This will include both the air-earth interface and the seafloor.
    10. Semi-automatic mesh control. This will warn user that the mesh may be inaccurate and suggest appropriate modifications.
    11. Interface for GEOTOOLS-MT.

THESE DOWNLOAD INSTRUCTIONS NO LONGER WORK: UPDATE SOON

How to get inv2d, the rapid 2D MT inversion program(commonly called RRI). use command:

ftp www.geophys.washington.edu

-or-

ftp 128.95.16.50

at login prompt type: anonymous

at password prompt type: your last name or userid

then type commands:

cd pub/out/RRI

get README.FIRST

mget Inv2d.news*

bin

VERY IMPORTANT: get newrri.tar

If you want the imagetool executable (see README.FIRST) get imagetool.Z

Finally, logout using bye

You now need to unpack the Unix tar file inv2d.tar using the command tar -xf inv2d.tar.
This will set up directory structure. There are several readme files and a runme file that will get you started.

Good Luck! John Booker

THIS DOWNLOAD NO LONGER WORKS: UPDATE SOON

You can also download the source directly using the following ftp link:- Download RRI Source Code