Barretto, J. ; Caratori Tontini, F. 2022 Total magnetic intensity grid of the upper North Island, New Zealand. Lower Hutt, N.Z.: GNS Science. GNS Science report 2021/47. 29 p.; doi: 10.21420/A520-NK43
Abstract:
A procedure for merging gridded airborne and shipborne magnetic data over the upper North Island has been formulated using Geosoft scripts. The two main products are an integrated total magnetic intensity (TMI) Geosoft grid with 100 m cell size and UTM 60S projection on the NZGD2000 datum and a master database containing the data from 37 individual surveys and from a TMI regional drape grid created from three regional grids. The integrated grid preserves the original TMI frequencies and observation elevations making it useful for forward and inverse modelling. The integrated TMI grid and database can be updated as new magnetic data become available by following the steps outlined in this report. Processing steps are divided into sections and sub-sections that address discrete actions, enabling only relevant subsets of the processing sequence to be run when grid updates are required. Oasis montaj software is the tool used for all processing steps. A Geosoft format database is used to store data, the MAGMAP module for grid filtering, the Compudrape™ module for grid continuation, and the Grid Knitting module for stitching grids. Oasis montaj is also able to export the master database and TMI grid into other formats and projections for output or to be read into other software packages. The procedures described in this report can also be applied for making integrated magnetic grids for a larger area such as the whole of New Zealand or from any geographic area. The processing sequence is also adaptable to produce other geophysical products, where single elevation drape grids are created for various geophysical analysis such as frequency analysis and curie point depth calculations. (auth)
