Glenn,

I may have sent you this previously, but it's further elaboration on how redshift would occur over distance;

http://fqxi.org/data/forum-attachments/2008CChristov_WaveMotion_45_154_EvolutionWavePackets.pdf

1. Introduction

The propagation of waves in linear dissipative systems is well studied but most of the investigations are concerned with the propagation of a single-frequency wave. On the other hand, in any of the practical situ- ations, one is faced actually with a wave packet, albeit with a very narrow spread around the central fre- quency. This means that one should take a special care to separate the effects of dispersion and dissipation on the propagation of the wave packet from the similar effects on a single frequency signal.

The effect of dissipation of the propagation of wave packets seems important because their constitution can change during the evolution and these changes can be used to evaluate the dissipation.

Especially elegant is the theory of propagation of packets with Gaussian apodization function.