THE FREQUENCY-AGILE RADAR - A MULTIFUNCTIONAL APPROACH TO REMOTE-SENSING OF THE IONOSPHERE

We introduce a new kind of diagnostic sensor that combines multifuncti onal measurement capabilities for ionospheric research. Multifunctiona lity is realized through agility in frequency selection over an extend ed band (1.5 to 50 MHz), system modularity, complete system control by software written in C, and a user-friendly computer interface. This s ensor, which we call the frequency-agile radar (FAR), incorporates dua l radar channels and an arbitrary wave-form synthesizer that allows cr eative design of sophisticated waveforms as a means of increasing its sensitivity to weak signals while minimizing loss in radar resolution. The sensitivity of the FAR is determined by two sets of power amplifi er modules: four 4-kW solid-state broadband amplifiers, and four 30-kW vacuum tube amplifiers. FAR control is by an AT-bus personal computer with on-line processing by a programmable array processor. The FAR do es not simply house the separate functions of most radio sensors in us e today, it provides convenient and flexible access to those functions as elements to be used in any combination. Some of the first new resu lts obtained with the FAR during recent field campaigns are presented to illustrate its versatility. These include (1) the first detection o f anomalous high-frequency (HF) reflections from a barium ion cloud, ( 2) the first evidence of unexpectedly large drifts and a shear north o f the equatorial electrojet, (3) the first HF radar signature of a dev eloping equatorial plasma bubble, and (4) the first measurements by a portable radar of altitude-extended, quasi-periodic backscatter from m idlatitude sporadic E. We also mention the potential of the FAR for at mospheric remote sensing.