Cross-channel sounding for HF geolocation: concepts and experimental results

Abstract

In the context of passive geolocation of High Frequency (HF) transmitters using the Time Difference of Arrival (TDoA) method, the transmitted signal and the propagation channel is unknown. This paper explains the principle of a method termed as "cross-channel sounding" along with its concepts. This method is used to evaluate the propagation duration differences of an unknown signal received by multiple synchronized distributed receivers. The mathematical description for cross-channel sounding is detailed, emphasizing the importance of the nature of the transmitted signal in the estimation of the propagation duration differences. An operational country wide TDoA receiver network capable of capturing HF signals is presented. HF broadcast signals are captured from different transmitters around Europe. Experimental data are used to analyze the different propagation modes from cross-channel sounding and assess the TDoA estimation complexity in the case of multipath channels.

Globally Optimized TDOA High-Frequency Source Localization Based on Quasi-Parabolic Ionosphere Modeling and Collaborative Gradient Projection

“…Despite data transmission restrictions in such a scenario and ubiquitous error-causing environmental factors like the multipath propagation and interferences, recent years have witnessed a growing number of successful TDOA receiver networks, operational for long-range HF geolocation. For example, Jain et al elaborate in [15] on their crosschannel sounding methodology for accessing the channel impulse response and evaluating the time delays. Experimental results of the corresponding prototype system can be found in [5].…”

“…Typically, the negative effects of biased sensor observations are mitigated either when measuring the TDOAs or in the subsequent step of location estimation. For example, carefully filtering the captured signals [4] and choosing the peak with the strongest signal level in cross-correlation [15] are both popularly used schemes that belong to the first category of approaches. The second category, on the other hand, might permit more flexibility.…”