Many interesting effects, e.g., the generation of short-wavelength plasma turbulence, can arise when ground-based transmitters irradiate the ionosphere with radio frequency (RF) waves. The thresholds and growth rates of these effects typically depend on the intensities of the pump fields, sparking interest in finding an inexpensive way to increase the intensities of these fields. A method has been proposed [Cowley et al., 1993> for generating a high-intensity RF pulse in the ionosphere by launching a frequency-chirped pulse of much lower intensity from a ground-based antenna. The dispersive properties of the ionosphere compress the pulse, generating a short, intense pulse. A one-dimensional model with a linear density profile has shown that pulse compression can lead to significant intensity enhancements, up to a factor of 100 over steady state field intensities. Pulse compression is modeled in ionospheres with more realistic density profiles than have been considered previously. A novel asymptotic technique is developed for finding wave packet solutions in general, slowly varying density profiles. Various factors affecting compression, such as launch frequency and frequency bandwidth, are discussed. Large pulse compression requires a good knowledge of the plasma parameters, particularly the plasma density near the compression point. The sensitivity to incomplete knowledge of the density profile is investigated. Information about the density profile is contained in the reflected pulse. A simple algorithm for obtaining this information is derived. ¿ American Geophysical Union 1996