A kernelized deep regression method to simultaneously predict and normalize displacement responses of long-span bridges via limited synthetic aperture radar images

Synthetic aperture radar (SAR) images retrieved by spaceborne remote sensing have recently gained significant attention as an affordable and effective solution to provide structural responses in terms of displacements from field measurements. Notwithstanding, this process may lead to partial/scattered information due to the limitations of SAR images. Furthermore, the effects of unmeasured environmental and/or operational conditions on structural responses and sensitivity of SAR-extracted displacements of full-scale structures like long-span bridges to these conditions still stand as major challenges. In this work, an innovative machine learning-aided methodology is put forward for handling these issues. The proposed methodology simultaneously predicts and normalizes displacement data within a two-stage kernelized deep regression (KDR) framework. The first stage involves kernelized regressor modeling and selection, exploiting Gaussian process regression and support vector regression. The second stage is based on deep regressor modeling via a long-short-term-memory neural network. The proposed methodology is shown to display high accuracy in prediction limited displacement data independent of unmeasured environmental/operational data. To concretely assess the performance of the proposed methodology, displacement responses from two long-span bridges and seasonal temperature records are considered. Results show that the approach is superior to available state-of-the-art techniques.