Introduction

This report contains aeromagnetic data for five areas in northern Wisconsin collected by the U.S. Geological Survey by means of a contract airborne survey, carried out between October 1997 and March 1998. Flights of the aeromagnetic survey were oriented in a north-south direction, at a spacing of 0.5-mile (805 meters), and draped to topography at 1,000 feet (305 meters) above ground. The five blocks of the survey required a total of about 21,000 line-miles of flying.

The aeromagnetic data include (1) point measurements taken at 1-second intervals, giving 15 fields of data in ASCII format, including flightline number, latitude, longitude, diurnally corrected magnetic intensity, residual (IGRF-removed) magnetic intensity, time, and altitude, (2) grids of residual magnetic intensity using a Transverse Mercator projection and given in several file formats, and (3) images of the aeromagnetic data and an index map, each given in four graphics formats.

Directory Organization

data

The basic survey measurements are in five ASCII files (file extension .dat) derived from the original contractor files. Each record of each file contains 15 fields of data per measurement, at a sampling interval of 1 second. USGS style DOS binary point files (.pos) with nine fields are also given. See the report for the explanation of each of these fields.

grids

The point data have been interpolated into binary raster USGS style grids (file extension .grd) by using a minimum curvature gridding algorithm (program MINC, Phillips, 1997). ASCII versions of the USGS grids are also given (.agd). USGS grids and binary point files can be manipulated using USGS (DOS) software for the PC (Phillips, 1997). This is freeware that is included in the usgs_pf directory. Two alternate ASCII file formats are also included. These ASCII grids permit importation into other software packages. Files with extension .arc can be imported into Arcview, and file extension .gxf can be imported into several programs including ER Mapper and Geosoft Oasis Montaj.

images

Images of the aeromagnetic data for each of the five areas covered by the survey are included in this directory and are given in four graphic formats (file extensions .ps, .pdf, .bmp, .jpg), the latter three derived from an initial PostScript image file.

usgs_pf

The USGS potential field software package (Phillips, 1997). Installation is described in the readme files.

Posted online October 15, 2009
CD originally published in 1999