Processing-Based Synchronization Approach for Bistatic Radar Glacial Tomography

We develop and test a bistatic radar system and processing chain that recovers weak echoes at large antenna separations, which is a necessary step towards high precision temperature inversions. Traditional ice penetrating radars have limited capacity to infer temperature distributions because monostatic measurements do not provide sufficient information to resolve the depth-dependent ice temperature profile. Bistatic radar introduces quasi-independent measurements that can address this challenge, but existing systems are unable to attain the large antenna separations necessary to resolve the small temperature gradients important to glaciological processes. Existing bistatic systems are either limited in antenna separation by losses in synchronization cables or by poor signal-to-noise-ratio (SNR) for unsynchronized systems. We address this challenge through coherent summation of phase re-aligned signals to recover the basal and internal layer reflections at large antenna separations without requiring hardware synchronization. The system consists of an Autonomous Phase-sensitive Radio Echo Sounder (ApRES) as the transmitter and a Software Defined Radio (SDR) as the receiver. We assess the system's capacity to achieve high SNRs and large offsets at Whillans Ice Stream, West Antarctica, with up to a 1.3 km antenna separation. This experiment charts a course for even larger antenna separations to resolve small temperature signals with high fidelity.