PACES has played a significant role in the compilation of gravity data in southwestern North America. This effort has been conducted in close cooperation with the U. S. Geological Survey, the National Geospatial-Intelligence Agency (formerly the National Image and Mapping Agency), National Oceanic and Atmospheric Administration, industry and academic colleagues. Together, we have developed the GeoNet gravity database portal that provides access to our new database for the U. S. The U. S. Geological Survey Open File report that describes this effort is available at this link: Open-File Report 02-463. The version now available is a major update to existing databases and is now also terrain corrected. This effort is also a key part of our NSF-supported projects to develop a geoscience cyberinfrastructure (GEON and SWGeoNet), and also features a tutorial "Getting Started: Using and Understanding Gravity Data".
The Data: The new terrain corrected United States gravity database is available through the GeoNet link below. The terrain corrections were calculated by Mike Webring of the U. S. Geological Survey using a digital elevation model and a technique based on the approach of Donald Plouff. The reduction of these data has been updated with modern geodetic datums and a higher precision digital elevation model. In the present version, latitude and longitude values are referenced to NAD83 (North American Datum 83; horizontal datum) and elevation values in meter are referenced to NGVD88 (Vertical datum).
Dr. Raed Aldouri
Base Stations: Our effort also includes archiving gravity base station information for the United States. This element of the portal includes the ability to download base station data and diagrams provided by Dan Winester of the National Geodetic Survey who has made a major effort to ensure that the base station descriptions are accurate and current. This information is based on a base station database maintained by the National Geospatial-Intelligence Agency. However, the two databases are not identical and a map of the NGA stations is provided via the link below. Information about specific stations can be obtained via the NGA website. This information is available from the links below:
Gravity Base Stations - Data and Diagrams
NORTH AMERICAN GRAVITY DATABASE EFFORT:
The obvious next step after the U. S. gravity database and North American Magnetic Map efforts is an improved regional gravity database for North America. Thus, an international effort by governmental agencies, universities, professional organizations, and private industry is underway to update the publicly available North American Gravity Database. The current database that was released roughly two decades ago needs revision to improve its overall quality, coverage, observation density, and versatility. Considerable data have been made available in the intervening period and improvements are possible in the calculation of gravity anomalies by taking advantage of available terrain and geodetic models and high-speed data processing procedures and facilities. Data will be made available in a web-based system as part of the U. S. Geoinformatics program and through other governmental agencies.
The database will have a comprehensive menu making it useful for those with differing scientific interests and backgrounds. The user will be able to select desired corrections to the gravity data, units used, datums employed, and type of gravity anomaly and retrieve information on the predicted errors in the data. The default gravity anomalies (in milligals) of the database based on internationally accepted datums and constants will be useful for geological studies and most geophysical investigations. Database fields and formats will accommodate the increasingly available high-resolution, airborne, satellite, marine, and gradient gravity data and will be updated as additional data are obtained and improvements are made in data processing. The database will be updated as additional data are obtained and improvements are made in data processing.
Click on the links below to see an initial report from the North American Gravity Database Committee of the Standards/Format Working Group, as well as recent publications about the implementation of these standards.