Description of estimation procedure for velocities.

[dpsnowden]

Before our next meeting with the data team we should have a good explanation of the estiamtion procedure for the segment averaged velocities on the wiki. Unanswered questions include:

1. Do we need to use cell methods to describe the averaging procedure?
2. We need working examples of THREDDS aggregations of both the time variables and the time_uv variables in order to determine if our approach is viable and to present it to the group.

John, I'm assigning these issues to you just to make sure you receive notification. Not sure how github works with issues yet. We should discuss.