EFFECTS OF ARTIFICIALLY MODIFIED IONOSPHERES ON HF PROPAGATION - NEGATIVE-ION CATION RELEASE EXPERIMENT-2 AND CRRES COQUI EXPERIMENTS

We report the results of measurements obtained in conjunction with a s eries of high-altitude chemical release experiments of effects of arti ficially modified ionospheres upon high-frequency, ionospherically ref lected radio paths. Computer simulations indicate that under optimum c onditions, ionospheric modifications induced by chemical releases coul d perturb or even disrupt a communication channel; our experiments cor roborate this but also indicate that it is very difficult to actualize such disruptions. Our experiments have shown that an ionospheric depl etion, in which the electron density hole forms a huge radio frequency lens, generates new modes which, however, do not significantly affect a communications system. Under optimum path geometry a signal strengt h decrease of 10 dB or more is possible for several tens of minutes. E nhancements, such as those produced by barium releases, act as reflect ing mirrors that can create a large shadow zone on the ground and bloc k off significant amounts of energy. We measured signal strength decre ases of up to 20 dB.