Sounds to me like you need to investigate signal processing algorithms commonly used in seismic processing that do spatial spectral decomposition. This paper
Dead Link Removed discusses some of the general theory involved.
The abstract quoted below is pretty self explanatory in its scope:
We present an extension of the generalized spectral decomposition method for the resolution of nonlinear stochastic problems. The method consists in the construction of a reduced basis approximation of the Galerkin solution and is independent of the stochastic discretization selected (polynomial chaos, stochastic multi-element or multi-wavelets). Two algorithms are proposed for the sequential construction of the successive generalized spectral modes. They involve decoupled resolutions of a series of deterministic and low-dimensional stochastic problems. Compared to the classical Galerkin method, the algorithms allow for significant computational savings and require minor adaptations of the deterministic codes. The methodology is detailed and tested on two model problems, the one-dimensional steady viscous Burgers equation and a two-dimensional nonlinear diffusion problem. These examples demonstrate the effectiveness of the proposed algorithms which exhibit convergence rates with the number of modes essentially dependent on the spectrum of the stochastic solution but independent of the dimension of the stochastic approximation space.
There are some public domain signal processing packages that are pretty tractable to anyone with basic ability to use unix and some rudimentary programming skills to construct some command line tools that will do the analysis you need. The software modules are available here:
http://www.freeusp.org/
The only issue is that you will need to write an input module to take the place of the standard SEGB input format. The DDS I/O system may be adaptable for this purpose.
The manual description for the basic spectral decomposition module is here:
http://www.freeusp.org/RaceCarWebsite/TheToolkit/Man_alphabetic/spec.html
and it is obviously just a simple 2 dimensional analysis. But since the source code is available, you could perhaps adapt it for your needs. It clearly does not provide the reduced basis Galerkin solution outlined in the first article mentioned.