I received some good input from Randall Barbour by email that he gave me the okay to share here.

Hi David:
Some general thoughts. Typically standards for data sharing serve two principal purposes; a basis for cross platform data review, and to facilitate the ability to reproduce experimental conditions. While perhaps already considered, particulars of the source-detector configuration would benefit from platform-dependent information that additionally identifies source-detector power/amplification details. For instance, all of our imagers support the ability to vary source amplitude as well as detector gain. Also adjustable is the timing of the source illumination sequence. For instance, large area investigations can be accomplished using either a single-point time multiplexing scheme or simultaneous multipoint, time multiplexing. In the limit, there are a large number of ways illumination-detection can be accomplished even for a fixed sensor layout. The way we deal with this is to have the user define the source detector configuration that pertains to each sub-array of the overall sensing geometry. Clearly, there would be a need to access this information, without which the data would not be interpretable.

Still another consideration looking forward are elements that pertain to data quality assurance. For instance, we routinely examine our gain setting values prior to collecting data as a basis for determining the fidelity of optode contact. It might be helpful to have the ability to include a metric that supports such measures as an objective basis for appreciating variations in head-gear setup.
I hope you find this helpful. Please get back to me if you need any additional clarifications.
Best,
Randall

My response:
Dear Randall,
Thanks for the input. Your points are clear. We should modify the spec to allow for information about source power and detector gain. I believe that the spec already handles variable illumination sequences. I'd be happy to review this with you to make sure I am not missing something.

So, the question is how best to modify the spec to handle source power and detector gain. These are not necessarily fixed parameters, like the their positions, since the power and gain can vary depending on the specific source-detector pair during temporal multiplexing. As such, it seems best to put this information into the measurement list 'ml' in data(idx).ml(chIdx).XXX . Every subfield in 'ml' is currently an index into the SD structure. So, we could either add
ml(chIdx).srcPower and ml(chIdx).detGain
or
ml(chIdx).srcPowerIdx and ml(chIdx).detGainIdx
where these indices would refer to new fields
SD.SrcPower and SD.DetGain
Thanks,
David


So, I am now about to incorporate this into the spec. I am leaning towards using
ml(chIdx).srcPower and ml(chIdx).detGain 
as this will be much more efficient than the latter option as indexing srcPower and detGain could become quite annoying as both power and gain can easily take on a continuum of values. All the fields currently indexed in the SD structure very clearly only take on discrete values.

I will make this addition to the ml structure for now, but encourage comments in support or against it.

Thanks,
David