Optimal Frequency Ratio Design Method for Multifrequency Phase Unwrapping of UAV InSAR

As an essential component of interferometric synthetic aperture radar (InSAR) measurements, phase unwrapping (PU) is a critical process that significantly impacts the accuracy and reliability of topography and deformation measurements. As an effective approach that can overcome the limitations of the Itoh condition, the multi baseline (MB) PU method is widely used in PU; however, when it comes to unmanned aerial vehicles (UAVs) InSAR systems that use a single antenna and repeat-pass mode for interferometric measurements, the time-varying baseline can pose a challenge since the airflow disturbance can prevent the repeat flight paths from remaining parallel. This makes the combination of baselines more complicated, which can impede the feasibility of using the MB PU for the UAV InSAR. As a result, using the relationship between different frequencies for PU is a promising alternative method. This article demonstrates that the frequency ratio design is a crucial factor in the success of the multifrequency (MF) PU method. An optimal frequency ratio design method for MF PU that maximizes the minimum Euclidean distance between the intersection vectors determined by the integer ambiguity vectors is proposed. The proposed method is validated using the simulated and experimental datasets, which provide evidence that PU accuracy can be greatly enhanced with the optimal frequency ratio.