transmission of overdense radio waves. This was done because previous studies (13) have shown that overdense heating produces obvious scintillation effects and the overdense observations can provide realistic comparison for the underdense observations. The results shown in Fig. 5 appear to indicate that ionospheric irregularities were created at a time the Platteville Facility was operating in an underdense mode and that these irregularities induced scintillation on the LES-8 signal that was received on board the Air Force Avionics Laboratory aircraft. The observations of the LES-8 transmissions at 249.2 MHz were repeated on April 14, 1980. The results obtained show that signal fluctuations of the type seen in Fig. 5 were observed during periods of underdense heating, lending credence to the results obtained in March, 1980. 4.2.2 Satellite-to-Ground Observations. During the time period that satellite-to- aircraft measurements were made, several satellite-to-ground experiments were performed. These experiments were conducted at Douglas, Wyoming, and Carpenter, Wyoming. The measurements program at Douglas involved the monitoring of the ATS-3 satellite transmission at 137 MHz using a polarimeter and monitoring the FLEETSATCOM transmission at 244.5 MHz using a 3-spaced receiver network. The experiment at Carpenter, Wyoming, was directed toward monitoring the transmissions from the LES-8 satellite at 249.2 MHz. The emphasis of the Douglas-based experiments was on overdense heating effects. The Carpenter, Wyoming, observations, on the other hand, were optimized to detect underdense heating effects, and for this reason, the only results discussed are the ones obtained at Carpenter. Figure 6 (following from Ref. 11) provides an example of the LES-8 signal observed on March 1, 1980, between the hours of 0024 to 0100 h (UT) at Carpenter, Wyoming. At 0030 h, the Platteville Facility was turned “ON” at a frequency of 9.9 MHz with an input power of 1.5 MW. The facility remained “ON” until 0045 h (UT). During this entire time period, f0F2 was near 12 MHz. Thus, the case illustrated represents overdense heating effects. The fluctuations seen between 0030 and 0045 h (UT) are definitely associated with the Platteville Facility operation. Peak-to-peak
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