Refractive Turbulence, Transient Electronic Disconnectivity, and Propagation Situational Awareness (PSA)

This paper examines the proposition that mission limiting propagation induced disconnectivity have important and fundamental turbulence and propagation physics issues to be investigated. We propose to call these aspects “propagation” situational awareness (PSA). Transient disturbances can also be present in communication to and from ground stations and satellites and in the perfo rmance of ground based and spacebased optical and infrared imaging and tracking systems. Propagation frequency is important in characterizing whether the source of the disturbance lay in the electron density fluctuations of ionosphere or the refractive turbulence of the neutral atmosphere. Over the past ten years high altitude airborne measurements of clear air and refractive turbulence were made in Australia t o support design and performance evaluations of the Airborne Laser. More recently in collaboration with the Australian Defence Science & Technology Organization (DSTO) two smaller aircraft were used to investigate the effect of ducting layers on the signal strength of an airborne emitter as low-cost measurements of potential for loss of track in the coverage pattern of an airborne radar. From 2002 onward we were also tasked to do fundamental investigations of clear air turbulence for flight safety evaluations of both manned and unmanned high altitude surveillance aircraft. these investigations were confined to measurement days and altitudes where strong turbulence was expected. The decision to measure was based on predictions of the location of jet streams relative to the measurement area as well as on bulk gradient Richardson (Ri) vertical profiles derived from radiosonde measurements from stations surrounding the potential measurement location. We will show how all these analyses and decision aids, including the Ri profiles, can be used to estimate potential for propagation disturbances in PSA. Current DOD interest in Transformational Communications Advanced Technology Study (TCATS), airborne networks, and joint space and airborne networks all can have crit ical Propagation Situational Awareness aspects under disturbed propagation conditions. Two-aircraft propagation measurements at X-band coupled with refractive and clear air turbulence measurements are planned jointly with DSTO in Australia in their winter season in 2009. These two-aircraft measurements are fundamental to developing a propagation situational awareness analysis scheme.