1	Frequently Asked Questions: Velocity Profile Pieces How does Depth Cell size control the variance of the Velocity Profile? Why do Range Gates overlap? What sets the Depth of the First Cell?
2	How does Depth Cell size control the variance of the Velocity Profile? Next 3 pages
3	Depth Cell size controls Velocity Profile Resolution and Variance. The user-selected size for Depth Cell sets the duration for Range Gate and Transmit, controlling (1) RESOLUTION of the Velocity Profile. This is set directly by the Range Gate size. (2) VARIANCE of the Velocity Profile. Variance varies inversely with the number of echoes heard in a Range Gate. As the next Figures show, the number of echoes heard varies with the product (Transmit x Range Gate). Depth Cell size sets each of these, however, so the number of echoes heard varies with the square of Depth Cell size. Thus Variance varies inversely with the square of Depth Cell size OR the standard deviation of the velocity data varies inversely with Depth Cell size.
4	Resolution & Precision (Figure)
5	Smaller Depth Cells
6	Why do Range Gates overlap? Next 2 pages
7	At any depth, the Transmit pulse persists for a period equal to the duration of the Range Gate (default). At a few depths, the arrival time of the Transmit pulse corresponds exactly with the start of a Range Gate. Echoes from those few depths* will be heard by just one Range Gate. At all other depths, the arrival of the Transmit pulse is not coincident with the start of a Range Gate. The Transmit pulse therefore radiates scatterers for a period that extends into the next Range Gate--causing the depth overlap noted in these slides. *These are the same depths assigned to Depth Cells in the Velocity Profile.
8	Range Gate Overlap (Figure)
9	What sets the Depth of the First Cell? Next 2 pages
10	The depth of the First Cell is set at its mid-point (not its top edge). First Cell depth can be altered by three settings of the ADCP: (1) Depth cell size (2) Transmit duration (3) Blank size Generally (default setup) Cell #1 depth = Blank depth + Depth cell + ADCP Immersion TIP: Setting small depth cells is the primary means to bring the First Cell closer to the surface.
11	Depth of First Cell (Figure)