Bayesian inference of spatially varying Manning’s n coefficients in an idealized coastal ocean model using a generalized Karhunen-Loève expansion and polynomial chaos

Adil Siripatana (1) , Olivier Le Maitre (2) , Omar Knio (1) , Clint Dawson (3) , Ibrahim Hoteit (1)

1 KAUST - King Abdullah University of Science and Technology [Saudi Arabia]
2 PLATON - Uncertainty Quantification in Scientific Computing and Engineering
3 University of Texas at Austin [Austin]

Bayesian inference with coordinate transformations and polynomial chaos for a Gaussian process with a parametrized prior covariance model was introduced in [61] to enable and infer uncertainties in a parameter-ized prior field. The feasibility of the method was successfully demonstrated on a simple transient diffusion equation. In this work, we adopt a similar approach to infer a spatially varying Manning's n field in a coastal ocean model. The idea is to view the prior on the Manning's n field as a stochastic Gaussian field, expressed through a covariance function with uncertain hyper-parameters. A generalized Karhunen-Loeve (KL) expansion, which incorporates the construction of a reference basis of spatial modes and a coordinate transformation, is then applied to the prior field. To improve the computational efficiency of the method proposed in [61], we propose to use two polynomial chaos expansions to: (i) approximate the coordinate transformation, and (ii) build a cheap surrogate of the large-scale advanced circulation (ADCIRC) numerical model. These two surrogates are used to accelerate the Bayesian inference process using a Markov chain Monte Carlo algorithm. Water elevation data are inverted within an observing system simulation experiment framework, based on a realistic ADCIRC model, to infer the KL coordinates and hyper-parameters of a reference 2D Manning's field. Our results demonstrate the efficiency of the proposed approach and suggest that including the hyper-parameter uncertainties greatly enhances the inferred Manning's n field, compared to using a covariance with fixed hyper-parameters.

Mots clés: Coastal ocean model; Manning's n coefficients; Bayesian inference; Karhunen-Loève expansion; Polynomial Chaos; MCMC

Domaines: Océan, Atmosphère; Océanographie; Mécanique des fluides [physics.class-ph]; Applications [stat.AP]

Adil Siripatana, Olivier Le Maitre, Omar Knio, Clint Dawson, Ibrahim Hoteit. Bayesian inference of spatially varying Manning’s n coefficients in an idealized coastal ocean model using a generalized Karhunen-Loève expansion and polynomial chaos. Ocean Dynamics, 2020, 70 (8), pp.1103-1127. ⟨10.1007/s10236-020-01382-4⟩. ⟨hal-03010151⟩