Blar i Bergen Open Research Archive på forfatter "Evensen, Geir"
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4D seismic history matching: Assessing the use of a dictionary learning based sparse representation method
Soares, Ricardo; Luo, Xiaodong; Evensen, Geir; Bhakta, Tuhin (Journal article; Peer reviewed, 2020-12)It is possible to improve oil-reservoir simulation models by conditioning them on 4D seismic data. Computational issues may arise related to both storage and CPU time due to the size of the 4D seismic dataset. An approach ... -
Data assimilation for coastal zone monitoring and forecasting
Evensen, Geir; Drange, Helge (Elsevier oceanography series. (EuroGOOS publication no. 7), Chapter, 1997) -
Deltidsstillinger på sykehjem - lederens interne vikarpool?
Evensen, Geir (Master thesis, 2011-12-14)Bakgrunn: Så mange som 70-90 % av ansatte i kommunal helsetjeneste jobber i deltidsstilling. Flere omorganiseringer de senere år har hatt som mål å effektivisere helsetjenesten og utnytte begrensede helseressurser bedre, ... -
A Hybrid Coordinate Ocean Model for shelf sea simulation
Winther, Nina Gjerde; Evensen, Geir (Journal article, 2006-03-03)The general circulation in the North Sea and Skagerrak is simulated using the Hybrid Coordinate Ocean Model (HYCOM). Although HYCOM was originally de- veloped for simulations of the open ocean, it has a design which should ... -
The impact of ensemble filter definition on the assimilation of temperature profiles in the tropical Pacific
Leeuwenburgh, O.; Evensen, Geir; Bertino, Laurent (Journal article; Peer reviewed, 2005-10)The traditional analysis scheme in the Ensemble Kalman Filter (EnKF) uses a stochastic perturbation or randomization of the measurements which ensures a correct variance in the updated ensemble. An alternative so called ... -
Indian Ocean: Validation of the Miami Isopycnic Coordinate Ocean Model and ENSO events during 1958–1998
Haugen, Vibeke E.; Johannessen, Ola M.; Evensen, Geir (Journal article, 2002-05-25)In the Indian Ocean, in situ data are sparse both in time and space. Therefore, numerical models are one of the major tools for further understanding of the ocean circulation. We have implemented, validated, and done a 40 ... -
Inverse Methods and Data Assimilation in Nonlinear Ocean Models
Evensen, Geir (Journal article, 1994-10-01)An overview is given of the current status of inverse methods and data assimilation for nonlinear ocean models. The inverse theory for time dependent dynamical models is formulated and the most promising solution methods ... -
Mesoscale modeling study of the oceanographic conditions off the southwest coast of India
Haugen, Vibeke E.; Johannessen, Ola M.; Evensen, Geir (Journal article; Peer reviewed, 2002-09)A high resolution model, using the Miami Isopycnic Coordinate Ocean Model (MICOM), has been implemented for the first time to study the seasonal circulation and coastal upwelling off the southwest Indian coast during 1974. ... -
Open Boundary Conditions for the Extended Kalman Filter With a Quasi-Geostrophic Ocean Model
Evensen, Geir (Journal article, 1993-05-18)The formulation of consistent boundary conditions for the quasi-geostrophic (QG) model with an extended Kaiman filter in a data assimilation scheme is discussed. To form a well-posed boundary value problem for the QG model, ... -
p-Kernel Stein Variational Gradient Descent for Data Assimilation and History Matching
Stordal, Andreas Størksen; Moraes, Rafael J.; Raanes, Patrick N.; Evensen, Geir (Journal article; Peer reviewed, 2021)A Bayesian method of inference known as “Stein variational gradient descent” was recently implemented for data assimilation problems, under the heading of “mapping particle filter”. In this manuscript, the algorithm is ... -
Parameter Estimation Solving a Weak Constraint Variational Formulation for an Ekman Model
Eknes, Mette; Evensen, Geir (Journal article, 1997-06-15)A weak constraint variational formulation is used for inverse calculations and parameter estimation in a one-dimensional Ekman model. When parameters in the model are allowed to contain errors, the inverse problem becomes ... -
Sequential data assimilation with a nonlinear quasi-geostrophic model using Monte Carlo methods to forecast error statistics
Evensen, Geir (Journal article, 1994-05-15)A new sequential data assimilation method is discussed. It is based on forecasting the error statistics using Monte Carlo methods, a better alternative than solving the traditional and computationally extremely demanding ... -
Using the Extended Kalman Filter with a Multilayer Quasi-Geostrophic Ocean Model
Evensen, Geir (Journal article, 1992-11-15)The formulation of the extended Kalman filter for a multilayer nonlinear quasi-geostrophic ocean circulation model is discussed. The nonlinearity in the ocean model leads to an approximative equation for error covariance ...