AIRYROOT: A Fortran program for calculating the gravitational attraction of an Airy isostatic root out to 166.7 km

This report describes a FORTRAN-77 program called AIRYROOT which calculates the gravitational attraction at sea level of an Airy isostatic root extending out to a radius of 166.7 km. The program incorporates an efficient algorithm devised by Parker (1912) which uses the fast Fourier transform to calculate potential field anomalies. Input is a rectangular grid in a projected coordinate system which contains values describing topography (elevations and depths in meters) or surface load (mass in g/cm2). Output is a rectangular grid of values of the gravitational attraction of the root in milligals (mGal). A strategy is outlined for combining this output with published results describing the attraction of the root beyond 166.7 km, for upward continuing the total attraction to appropriate observation elevations, and for subtracting the result from Bouguer gravity data to produce an isostatic residual gravity map. This program can also be used to make complete Bouguer corrections to marine gravity data given appropriate bathymetric data sets.