The investigators will develop a radar capability for the new Arecibo high frequency (HF) ionospheric heating facility using off-dish interferometric receive techniques. They will also explore using an on-dish receive mode that would require a T/R (transmit/receive) switch. The off-dish interferometric receiver systems would employ small arrays of active antennas and, after the initial analog filtering, a fully digital receiver system. Both the on and off-dish receiver systems could be used simultaneously yielding the most sensitive system. This radar system will enable new science by adding capabilities to conduct studies of meteor physics. Recent discoveries have shown that the vast majority of meteoroids visible as radar meteors fragment rather than simply ablating. This process is a likely source of important nanometer ?dust? in the 80-130 km altitude region where meteors ablate. The radar would be used in conjunction with the 46.8 MHz and 430 MHz radars at Arecibo to explore fragmentation. The combined measurements would allow studies of the radiowave scattering mechanism in meteor trails, and the processes whereby meteors deposit important metals in the atmosphere. Other important science areas include studies of mid-latitude spread-F, sporadic-E instabilities, quasi-periodic echo (QPE) structures, low-altitude quasi-periodic echoes (LQPE) structures, and the D-region ionization enhancements associated with lightning. The instrument could also find application as an MST (Mesospheric-Stratospheric-Tropospheric) radar and as a potential transit solar corona radar at solar minimum. Extending the HF heater capabilities to include a radar mode will enable much new science from the Arecibo instrument cluster. The HF-radar will allow direct probing of D-region heating effects, and possibly detection of lightning-induced D-region ionization. The effort will provide new opportunities for student research involvement by further enabling common-mode multi-radar campaigns and by supporting on-going model development efforts. Undergraduate students will be involved in building and fielding the system that will be available to all user communities, including students from collaborating institutions.
The research activity under this grant has been directed towards the use of the new Arecibo Observatory High Frequency (HF; 5 – 8 MHz) ionospheric modification or heating system to provide an on-dish HF radar mode. This radar mode, while harking back to the earlier days of ionospheric research, greatly leverages aeronomic research at Arecibo and elsewhere by introducing new technology as well as new observing modes. However, as the heater has remained under construction, this project evolved towards a more general HF radar capability that has in turn suggested a whole new HF radar concept that will be tested under future funding. This evolving approach points to relatively simple—and cheap—HF radar systems that may be simply deployable. In particular, the initial HF radar capability has been successfully implemented using the AO ionosonde as the transmitter. This approach enables immediate basic science involving passive ionogram generation. That is, while not controlling the ionosonde, this prototype radar "borrows" the ionosonde signal. This approach has demonstrated the viability of the active antenna system and of the Software Defined Radio receiver and signal analysis system. The next instrumentation step—given sufficient funding—is to add two additional antennas/receivers systems to allow experimentation with various interferometric modes including IDI (imaging Doppler interferometry) and the new radar concept mentioned above. All instrumentation developed under this effort is available for community use under a collaborative agreement. This grant supported several undergraduate students and one MS thesis as well as two journal papers along with two posters given at the 2013 CEDAR (Coupling, Energetics, and Dynamics of Atmospheric Regions) Workshop.
