We describe a method for removing ionospheric effects from single-frequency
radio data a posteriori. This method is based on a theoretical climatological
model developed by the USAF, which returns electron density as a function of
position and time along the line of sight to the source. Together with a model
of the earth's magnetic field, ionospheric delays and Faraday rotation values
ensue. If contemoraneous ionospheric data -- GPS TEC observations or ionosonde
profiles -- exist, they can be incorporated to update the modeled electron
densities.Comment: 6 pages, 2 fiugres; LaTeX2e (96/12/01); uses elsart.cls (2.15,
98/07/15); to appear in New Astronomy Review
