HR: 12:05h
AN: NG42A-08    [Abstracts]
TI: Variational Data Assimilation and the Indirect Representer Method: Application to crustal geodynamics
AU: * Egbert, G D
EM: egbert@coas.oregonstate.edu
AF: Colleg of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg Oregon State University, Corvallis, OR 97331-5503 United States
AB: One standard approach to DA, now well developed in the atmospheric and oceanic sciences, is to prescribe error covariances which define a priori hypotheses on the magnitude and spatial structure of model and data errors, and then optimize the tradeoff between fitting the data and satisfying prior model assumptions by minimizing a quadratic penalty functional. Minimization of such a penalty functional using gradient based search methods is often referred to as variational data assimilation, 4D-Var, or the generalized inverse method (GIM). The GIM has proven to be particularly well suited to scientific (as opposed to operational) studies in oceanography, and this approach is likely also to prove very useful for a wide range of scientific studies in geodynamics. Over the past decade optimization methods that make GIM more practical for large non-linear DA problems have been developed and applied in oceanography. These so-called "indirect representer" methods involve minimization of the quadratic penalty functional through a series of conjugate gradient solutions of the linearized Euler-Lagrange equations, recast in the data space. A modular implementation of the indirect representer approach, the Inverse Ocean Modeling (IOM) system, is currently being developed through an NSF funded ITR project. This modular system simplifies implementation of the GIM for any client dynamical model, but requires coding of a tangent linear (TL) to the non-linear dynamical model along with the adjoint (ADJ) of this TL. I will summarize the GIM approach to DA, the indirect representer method, and the IOM. As a specific application in geodynamics, I will discuss development of TL and ADJ codes, and coupling with the IOM, for the Geophysical Finite Element Simulation Tool (GEOFEST), which has been extensively used for visco-elastic modeling of Earth deformation associated with the earthquake cycle. One important lesson from this experience is that with reasonably modular modeling code, development of TL and ADJ codes need not be so onerous as to preclude consideration of gradient based search methods.
DE: 0594 Instruments and techniques
DE: 3260 Inverse theory
DE: 8194 Instruments and techniques
SC: Nonlinear Geophysics [NG]
MN: Fall Meeting 2005