An automatic method has been developed to allow a density map of the terrain to be easily generated, once an FTG or Falcon survey has been undertaken. The other required data is the terrain correction estiame at each survey observation point in the database, assuming a density of 1 g/cc.
The new algorithm relies upon there being a strong correlation between the terrain and the measured tensor components.
When more than 4 components are each showing similar correlations, the scaling factor is assumed to be the density.
The other requirement is there needs to be a minimum level of signal in the average amplitude of the components.
All of the work is done using the Calculation / expression builder in the dbedit or spreadsheet tool.
A new field can be created with the results being set by the following example expressions.
Part A. generating a density map
The simple expression
density = "T_fa_lev_MCP_tensor / TC_100_MCP_tensor"
is used to set a new or existing scalar field with estiamtes of the density or to NULL if not enough support for an estimate can be made.
Simply grid this density field to create a terrain density map.
Part B. applying the required density
The simple expression
TEST2p2_tensor = "(T_fa_lev_MCP_tensor) - (TC_100_MCP_tensor) * 2.2"
is used to calculate a new tensor field with the terrain correction at a fixed density, once the required judgement is made as to what density best suits your purpose.
 | NB The rule is the most complex data type must appear first in the expression eg tensor * scalar and not the other way around |
This ends up being resolved correctly by the C++ compiler when the arithmetic is done this way.
This is not spelt out in any of the documentation as yet.