Comprehensive knowledge of the Earth's gravity field is a fundamental requirement for geoid determination and establishment and maintenance of modern spatial reference frames and standards in Canada. Gravity is also a fundamental parameter for the geophysical characterization, structural interpretation, and imaging the deep crust of the Canadian landmass and continental shelves. The gravity program is national in scope with international linkages. It comprises five main program components.

1. The gravity mapping program has two components:
   • a systematic reconnaissance scale gravity survey of the Canadian landmass and continental shelves, and
   • more detailed gravity surveys of selected target areas performed by the Geological Survey of Canada.

   All surveys employ modern gravimeters and electronic positioning systems operating from ground, air, and sea platforms.

2. An innovative gravimetry program maintains instrumentation, and establishes absolute gravity measurements for gravity and geodetic networks and for geodynamic investigations.
3. The gravity standards program maintains a national gravity control station network, the Canadian Gravity Standardization Net (CGSN), which is tied to the International Gravity Standardization Net 1971 (IGSN71). The CGSN will also be increasingly tied to the Canadian Base Network. The university-owned Canadian Superconducting Gravimeter Installation (CSGI) is maintained and operated by the program at the Canadian Absolute Gravity Site (CAGS). This unique Canadian facility monitors variations in the Earth's gravity field with periods of seconds to years and contributes to studies of the physics of the deep interior of the Earth.
4. Maintenance and improvement of the Canadian geoid is a key responsibility of the national gravity program. A new Canadian geoid model, CGG2000, was released in 2001. The new model is a refinement of the previous model, GSD95, and continues to use the same format, grid spacing, and GRS80 reference ellipsoid (as used to define the NAD83 datum).
5. Gravity data are maintained in the Canadian Gravity Database (CGDB) containing more than 700,000 gravity observations collected from across Canada. Data are currently distributed to clients by NRCan's Geophysical Data Centre (telephone 613 995-5326, fax 613 952-8987, e-mail infogdc@agg.nrcan.gc.ca). Incorporation of the CGDB into the Canadian Geodetic Information System is now in progress.

The national gravity program offers consulting services and products related to gravity surveys and gravity data processing: e.g. absolute gravity measurements, instrumentation for marine gravity surveys, geoid computations, training and consultation in gravity field procedures and data processing, digital gravity data for Canada, gravity control station data and descriptions for CGSN, and colour gravity maps.

For additional information.