FREQUENCY-SHIFTED SIGNATURE OF THE HF PUMP IN THE IONOSPHERIC FOCUSEDHEATING EXPERIMENT

Ionospheric heating experiments have begun to examine interactions at altitudes where the heater HF wave frequency matches the local electro n plasma frequency. We discuss the frequency-shifted signature observe d by radiowave receivers on a rocket launched into the HF beam and app roaching the interaction altitude. The frequency shifts associated wit h the upgoing (transmitted) and the downgoing (reflected) waves arise from the Doppler effect and changes in the wave vector. The characteri stic spectral signature provides a method to locate the reflection alt itude accurately. Generally, the ratio of intensities of upgoing and d owngoing waves decreases as the reflection altitude is approached.