Detection and Localization of Closely Spaced Pipelines Using a 3-D Multistatic Subsurface SAR

Detection and localization of buried pipelines is an important problem for oil and water distribution industries as well as for excavation and construction companies. A novel 3-D forward scattering model and dynamic grid search-based inversion algorithm of multiple buried pipelines using multistatic synthetic aperture radar (SAR) configuration is demonstrated in this article. Traditional imaging algorithms that focus the SAR signal by compensating only for the phase work well when the targets are far away from each other. By considering both the phase and amplitude of the scattered field and casting the inversion problem as an optimization problem, the detection and localization resolutions are improved for extended targets. A forward scattering model for multiple adjacent pipes is developed to track the scattering phase centers (SPCs) of each pipeline as the receiver location is changed. The model is used to calculate the resulting propagation phase and amplitude attenuation due to propagation in lossy media. The misfit between the measured data and the forward model (FM) is used as the cost function. The cost function is minimized by the dynamic grid search algorithm that starts with an initial focus and then performs a more careful search to detect closely spaced pipelines. The FM and inversion algorithm are validated and compared with a basic focusing algorithm using full-wave simulations as well as experimental data for both metallic as well as dielectric pipes. The results show improvement in range and cross-range detection and localization resolutions over the basic SAR focusing algorithm.