Sensitivity analysis and calibration of a Lagrangian particle tracking using GPS-tagged drifters

Abstract

A Lagrangian particle tracking module within a hydrodynamic model in Environmental Fluid Dynamic Code Plus (EFDC+) was used to track the movements of large floating marine carcasses. This research used data from six GPS-tagged drifters collected in April 2017 by NOAA to conduct a sensitivity analysis and calibration on the Lagrangian particle tracking module. These analyses investigate the influence of specific parameters, notably wind drag and number of vertical layers in the model. Changing these parameters resulted in observable changes in the trajectories of tracked particles. The results of the sensitivity experiments were compared using the Skill Score statistic. Adding wind drag to the LPT was a pivotal alteration, augmenting the model predictive capabilities by increasing the Skill Score value from 0.23 to 0.47. Further tests examined the impact of varying wind drag coefficients (A and B) which are the slope and y-intercept of a linear equation used to describe overall drag coefficient (CD) as a function of wind velocity. These coefficients are employed in EFDC + software and altering them revealed that coefficient A has a larger impact on the model predictions compared to coefficient B. Finally, the transition from a 2D to a 3D model had a more significant impact on the results compared to increasing the number of vertical layers in the 3D configuration. However, the findings indicated that changing the model from 2D to 3D may not yield a large enough improvement in accuracy that would justify the additional computational demands associated with a 3D model when running long periods of time (several years). The study results have valuable implications for developing accurate and precise models of hydrodynamic systems emphasizing the importance of wind in LPT models and the efficiency of 2D vs 3D models for LPT simulations in the Mississippi Sound area.