WMM model coefficients time range

[s-pearce]

The World Magnetic Model (WMM) that was added to calculate magnetic declination for other functions relies on a coefficients file WMM.COF that is only valid for a 5 year period following the publication of WMM.COF. As of right now there appears to be no checks in the code to make sure that WMM.COF is up to date, or that the measurements fall within the 5 yr range that a WMM.COF is valid.

Perhaps the code should raise an exception if either values do not fall within the 5 yr range, or the current coefficients are out of date.

Additionally, either there is a need to support and maintain old WMM.COF files for magnetic declination from any OOI time range, or there needs to be the ability to store calculated magnetic declination values in the coverage model.

[s-pearce]

This does not need to be done soon. I just wanted to get an issue going so that it becomes known.
Hmm in hindsight perhaps I should have created a Jira ticket to alert all of OOI about the issue.