Parameter Reference Model

Use Constraints > Add Constraint > Parameter Reference Model or Parameter Reference Model > Modify to define the model that the inversion will tend towards, if there is no influence from the data.

Modify Parameter Reference Model Constraint dialog box options

Constraint type

By Default the parameter reference model is set to zero for all voxel elements. If the inversion model type is MVI then all three components of the vector voxel model elements are set to zero. For all model types other than MVI, you may provide a Constant other than zero for the entire model. You may have a prior knowledge of the characteristics of the study area, where as the geophysical response of the area is generally high and setting this value to a value >0 may speed up the process. Alternatively if you have derived through earlier processes a plausible Voxel model for the study area, you may choose to provide it instead. For the MVI model types, the Constant option is not available, because conceptually it is difficult to derive. If you however have created through earlier processes a plausible Vector Voxel model for the study area you may select it.

Filename

If theVector Voxeloption for MVI or the Voxel option for the other model type has been chosen, you are prompted to provide the name fo the file that defines the gradient model. This file is re-gridded to the VOXI document mesh interval and extrapolated to the extents of the padded mesh.

The parameter reference model is often used as the Starting Model.

Application Notes

The parameter reference model is used together with the Parameter Weighting constraint. It is the model to which the inversion will tend towards in the absence of influence from the data. The effect of the target model is usually most pronounced at depth or when the data are sparsely sampled.

There are two end member situations: the user knows nothing about the physical property distribution in the inversion domain; or the user has a good model of the physical property distribution in the inversion domain, perhaps from extensive drilling. In the former case, the Parameter Reference Model can be set to zero, whereas in the latter case, that known physical property model should be used as the Parameter Reference Model.

The fundamental difference between a Starting Model and a Parameter Reference Model is that the former is entirely subject to change, while the latter, subject to other constraints, will have regions where it is kept constant or highly resistant to changing.