Abstract
Assessing tidal stream energy resource typically involves the application of numerical models calibrated against sparse Acoustic Doppler Current Profiler (ADCP) data. This introduces significant challenges in energetic sites which are prone to significant spatiotemporal variations, like the Pentland Firth, Scotland, which is home to the world's highest capacity commercial tidal array. This study investigates the implications of limited calibration data and examines different approaches for constructing an appropriate friction field in tidal hydrodynamics model calibration. We compare performances between models using uniform and sediment-based friction coefficient fields and introduce the first application of adjoint-based calibration for optimizing a resource assessment model based on velocity data. The adjoint approach is applied iteratively and adjusts the friction coefficient with successive ADCP surveys. Our results demonstrate that the most widely applied approach employing a uniform friction coefficient fails to deliver adequate predictive performance across multiple data sets, even at close proximity. In turn, initial adjoint-based calibrations are prone to overfitting, which is rectified only with additional data acquisition. Simultaneously, calibration to solely the channel of interest could lead to significant inaccuracy in kinetic energy fluxes and thus greatly impact upper bound estimates on the resource and array-array interactions. These findings highlight the critical need for extensive and strategic ADCP data collection, which significantly reduces uncertainty and enhances model reliability, advancing the fidelity of coastal ocean models as in the tidal energy application we consider in this study.