Ionosphere sensors

Modification of the ionosphere with radio waves - the pioneering ionospheric heater/phased array of Platteville (Boulder, Colorado), predecessor of HAARP 

Modifying the ionosphere with radio waves” by W.F. Utlaut

 New Scientist 55, No 808, p.288-290 

Reading notes

The Platteville Atmospheric Observatory near Boulder, Colorado was one of the first major ionospheric heaters in the world. Linked to the Institute of Telecommunication Sciences (ITS) and the U.S. Department of Commerce and Telecommunications, it operated from 1968 to 1984 on ionospheric processes. It is still operational performing wind profile studies. The transmitting aerial array consisted of 10 elements forming a ring of 110 cm in diameter. Using an effective radiating power of 100 MW, the upgoing power would be distributed over a circular area in the ionosphere of 100 Km in diameter with an approximate power flux density of less than 50μW/m2. The installation was designed to perform ionospheric modification with frequencies from 5 MHz to 10 MHz using right or left circular polarization. It was found that depending on the polarization, there were different profiles of velocity and paths transversed during propagation. Right polarization was associated to “ordinary waves” and O-mode, while left polarization to “extraordinary waves” and X-mode. 

When modification was performed with X-mode excitation, electron temperature would increase by 35% in the F-region area attained by the beam. Detection of electron heating was quantified by the attendant effect on the rate of dissociation-recombination of electrons and molecular oxygen ions which leads to the 630 nm emission of oxygen (red line) and the generation of air glow.  For this process, the reaction rate is inversely proportional to electron temperature so that the emission intensity decreases compared to background when the temperature is rapidly increased, and increases after the heater is off. Experiments showed that the increase and decrease of electron temperature occurs within tens of seconds.

When modification was performed with O-mode excitation, there was an unexpected and nearly opposite result; there was an increase in the 630 nm (red) oxygen line after power-on and decrease after power-off. The generation of airglow (enhancement of natural airglow) implied that electrons excited oxygen by collisions. For this process, significant numbers of electrons with energies greater than 2 electron volts (eV) are required, when the ambient level is approximately 0.5 eV. Enhancement of other emission lines indicated that some electrons obtained energies equal to perhaps 10 eV. These processes appear to require generation of plasma "parametric" instabilities. The term "parametric" refers to the periodic modulation of a certain parameter of an oscillating system with sufficient amplitude at a certain frequency to cause the oscillation to become unstable.

Figure 1:  Transmission and reception of a signal using ionospheric-related mechanisms (Source).