Characterizing the Impact of Ionospheric Wave Structures on Coordinate Registration.

ABSTRACT: Coordinate Registration (CR) of OTHR targets requires accurate real-time ionospheric modeling coupled with HF propagation calculations to convert radar-measured target signal delays and beam steers to geographical position. Our team is the developer of one of the most sophisticated ionospheric data assimilation capabilities currently in existence, GPSII (GPS Ionospheric Inversion; pronounced"gypsy"). Our team is also very experienced in developing algorithms for OTHR CR; we have developed an extensive computational HF propagation tool set. One of the major limitations in CR accuracy is the inability of current CR algorithms to properly account for traveling ionospheric disturbances (TIDs). Our previous investigations into TID mitigation produced a number of tools and ideas that we here propose to architect into a significant advance in TID mitigation. In Phase I we will develop an HF propagation simulation capability that combines models of TIDs with 3D ray tracing to allow generation of simulated TID-affected OTH radar data (vertical and oblique ionograms, backscatter ionograms, Doppler-shifted surface clutter, delay and angle effects on targets, etc.). These simulated data will be used to demonstrate the effectiveness of ionospheric data assimilation in reconstructing the ionospheric TID structure affecting OTHR measurements, leading to Phase II development of an operational capability. BENEFIT: An ionospheric data assimilation method with the fidelity to model TIDs in real time will allow improved OTHR Coordinate Registration accuracy. Improved CR accuracy will enhance the applicability of OTHR as a wide area surveillance asset for Air Force and Homeland Security applications with dramatic cost savings over alternative microwave radar solutions. In the US counter drug mission of the current ROTHR system, it is necessary for intercepting aircraft to perform"cold-nose intercepts"where onboard radars are deactivated (so traffickers won"t detect the interceptors and dump their contraband to evade arrest). To visually spot the target aircraft, it is necessary for the OTH radar to guide the intercepting airplane to within a couple of kilometers of the target. However, TID-caused coordinate registration errors can easily be several tens of kilometers, so mitigation of these errors would have immediate benefit to the existing ROTHR system. Planned use of next-generation OTHRs for cruise missile and ballistic missile detection and trajectory estimation will benefit by mitigation of TID-induced CR errors to achieve sufficient accuracy for handoff to millimeter wave radars and IR sensors. While achieving good TID mitigation for OTHR is primarily our Phase II goal, the propagation simulation tools developed under Phase I will benefit the Air Force by providing the ability to perform studies in simulation to demonstrate the utility of OTHR as a surveillance asset in stressing TID environments.