  We discuss the numerically stable, spectral-domain computation and extraction
of the scattered electromagnetic field excited by distributed sources embedded
in planar-layered environments, where each layer may exhibit arbitrary and
independent electrical and magnetic anisotropic response and loss profiles.
This stands in contrast to many standard spectral-domain algorithms that are
restricted to computing the fields radiated by Hertzian dipole sources in
planar-layered environments where the media possess azimuthal-symmetric
material tensors (i.e., isotropic, and certain classes of uniaxial, media).
Although computing the scattered field, particularly when due to distributed
sources, appears (from the analytical perspective, at least) relatively
straightforward, different procedures within the computation chain, if not
treated carefully, are inherently susceptible to numerical instabilities and
(or) accuracy limitations due to the potential manifestation of numerically
overflown and (or) numerically unbalanced terms entering the chain. Therefore,
primary emphasis herein is given to effecting these tasks in a numerically
stable and robust manner for all ranges of physical parameters. After
discussing the causes behind, and means to mitigate, these sources of numerical
instability, we validate the algorithm's performance against closed-form
solutions. Finally, we validate and illustrate the applicability of the
proposed algorithm in case studies concerning active remote sensing of marine
hydrocarbon reserves embedded deep within lossy, planar-layered media.
