The experience of integrating of GIS techniques in the construction of digital maps of geophysical fields

The creation of digital data banks and the computer modeling of sites (the replacement of field matrices with their analytical approximations) did not abolish the role of maps in the visualization and analysis of data. However, the results of the digitization of maps are ambiguous due to the dependence on the method of interpolating of the field isolines. The present analysis is devoted to the study of methods of authentic mapping of isolines.

The methods of smoothing isolines are studied: an adjoining parabolic spline, a Bezier spline, a cubic spline on a regular rectangular grid, and linear interpolation for comparison purposes.

It is revealed that the interpolation with cubic curves preserves the continuity of the curve, but violates the continuity of the first derivative at the interpolation nodes, as a result of which breaks in isolines are seen.

Comparison of the results of digitization of gravimetry data by different methods has shown that none of the methods of gridding approaches any exact solution. The method of the radial basis function for complex contours has an acceptable accuracy. The kriging method will be such in the case of fine tuning of its parameters on the characteristics of the object. To create a reliable observation network, additional settings are needed, which are discussed in the report.

The actual values of the field, reconstructed by different interpolation methods, give different anomalies. Almost the same kinds of anomalies are in pairs of methods “kriging – function of a radial basis,” and “triangulation – natural neighbor.” The nearest neighbor methods, polynomial, mo-ving average, Shepard’s are unsuitable for the restoration of gully type isolines with a high degree of ruggedness.

The output from the ambiguous field visualization is on way of a two-stage preprocessing of the initial data: fine-tuning of the gridding parameters for a specific survey and the controlled nonlinear filtering of data in the GS Surfer. Here, unwanted local effects can be removed by smoothing low-pass filters, while highlighting local parts done with high-pass filters providing the filter parameters are set correctly. The choice of filters depends on the physical parameters of the media and is carried out by the cut-and-try method.

Binding of coordinates and digitization of isoline maps with contour rupture cannot be solved in GS Surfer. However, the strategy of creating of digital gravity databases was developed, which uses not maps of isolines, but a measurement logs, transferring a grid of values into the grid of anomalies. Software for processing maps with a contour gap has been developed and tested on the simple examples.