FS–238–95 OCTOBER 1997

Potential-Field Computer Programs, Databases, and Maps

Introduction


Scientists of the U.S. Geological Survey 

(USGS) have written computer software to process and interpret geophysical data, including 

gravity and magnetic (potential field), radiometrics (gamma ray), electromagnetics, remote 

sensing, spectroscopy, borehole geophysics, 

and shallow seismic data. They also have compiled gravity, magnetics, and radiometric data 

for large areas of the United States.

	 U.S. Geological Survey Open-File Report 

95–77 is a bibliography that lists many of these 

programs and databases. This fact sheet 

describes some of the most useful ones for 

potential-field data.

Potential-Field Databases


Publicly available gravity and magnetic 

data for the United States include Bouguer 

gravity station data (as point data or grids), 

aeromagnetic flight-line or gridded data, or 

both. A CD-ROM, USGS Digital Data Series DDS–9, contains gridded gravity, magnetic, and topographic data for the conterminous 48 States. Additional data sets, often 

gridded at a smaller interval, are available 

for many States or regions. Maps made from 

these gravity and magnetic data sets, and 

other related maps made by using techniques 

to enhance features of interest, are published 

for many States at the scale of the geologic 

HAWAII

ALASKA
map. Open-File Reports 

91–370 A–F list bibliographies and location maps of 

original aeromagnetic surveys covering the United 

States.

Potential-Field Programs

	 A separate fact sheet 

describes potential-field geophysical software for the PC 

(personal computer) that is 

available either as diskettes 

(Open-File Report 92–18 A–G) or on CDROM (DDS–9)

	 Open-File Report 93–560 A–D consists of 

materials provided for a workshop on geophysical map interpretation using the PC, including 

programs to use with potential field, radiometric, and remote sensing data sets. Data collected in the Osgood Mountains, Nevada, to 

study the Getchell gold trend are used to demonstrate the programs and methods included in 

this report.

	 In addition to the packages of potentialfield software in the three reports listed above, 

there are individual programs that prepare and 

interpret potential-field data. Some of these 

programs estimate depth to a geologic source 

by analyzing magnetic profiles. Other programs compute the magnetic field over a topographic surface or calculate corrections for the 

effect of terrain on magnetic anomalies.

	 Several interactive modeling programs calculate forward or inverse, 2- or simplified 3-

dimensional geologic models using gravity or 

magnetic data or both. These programs help the 

geoscientist interpret data by constructing geological bodies that account for anomalies, calculating the expected field, and matching the 

results with the known field.

	 Magnetic values depend on aircraft altitude 

and whether the survey was flown at a constant 

barometric elevation (such as 9,000 ft) or at a 

constant terrain clearance (such as 1,000 ft 

above the ground, also called draped surveying). Neighboring surveys may have been 

flown at different specifications. In order to 

compare anomalies from different surveys, 

several programs provide methods to calculate 

potential-field data on different surfaces (higher/lower surfaces, or level/draped surfaces).

	 Deeply buried geologic sources causing 

potential-field anomalies have broad, lowamplitude anomalies, whereas shallow 

sources usually cause narrow, high-amplitude anomalies. This characteristic allows the

geoscientist to analyze anomalies based on 

wavelength and amplitude. Some programs 

mathematically filter data to selectively 

remove anomalies caused by either deeper or 

shallower sources.

	 Gravity reduction programs calculate 

known factors that affect gravity meter readings, such as distance from the Earth’s center, the effect of land above sea level, tidal 

attraction, and local terrain. Some programs 

calculate an isostatic correction based on 

topographic models of buried, low-density 

mountain roots below areas of high elevation.

	 The USGS REMAPP system is a series 

of programs to process satellite and aircraft 

imagery data acquired by government or 

commercial sources. Image processing programs developed for remote sensing data 

include various mathematical operations, 

image statistics, data enhancements, ratioing, 

and masking. Potential-field data can be 

treated as image data, and these REMAPP 

programs can display or enhance certain 

characteristics of potential-field anomalies 

that may be hard to see in a simple contour 

map.

Availability

	 The current release of potential-field 

software package for PC and several other 

programs, and the bibliography of programs 

and databases (U.S. Geological Survey 

Open-File Report 95–77) are available at: 

http://minerals.er.usgs.gov

Additional Information

Viki Bankey

U.S. Geological Survey

Box 25046, MS 964

Denver Federal Center

Denver, CO 80225

(303) 236-1348

Fax: (303) 236-1425

viki@musette.cr.usgs.gov

Pat L. Hill (same address)

(303) 236-1343

pathill@musette.cr.usgs.gov