YSI SonTek RiverSurveyor, System Manual

Page: 34 / 194

SonTek/YSI Inc
RiverSurveyor System Manual (May 1, 2007)
22
Cell Size
Beyond the blanking distance, the ADP averages its data over a user-specified number of data
collection points known as
cells (also referred to as range cells or depth cells ) The size of these
cells is determined by a user-selected cell size . The cell size (commonly abbreviated as CS) de-
fines the resolution of the velocity profile (in meters or feet).
Keep in mind there are advantages and disadvantages to selecting small or large cell sizes:
•
Small cells allow you to get higher-resolution profile data, especially in shallow water.
However, more small cells are needed to profile to a specific range, which means that indi-
vidually analyzing small-cell data can be a time consuming process.
•
Large cells make data analysis of individual cells easier. However, the resolution of the pro-
file will be lower, which could make it more difficult to analyze shallow water data.
The data collected within a cell is averaged to the center of the cell. The distance from the ADP
to the center of each cell can be determined using the formula:
Distance to center of a cell = BD + N * CS
where:
BD = Blanking distance
N = Number of the cell (Cell 1 is the cell closest to the ADP)
CS = Cell size
Number of Cells
The number of data collection points to be recorded is determined by the user-selected number of
cells (commonly abbreviated as NC or Ncells). Data for up to 100 cells can be collected; typical
values for this parameter are between 10 and 30 cells.
The total profiling range of the system (to the end of the last cell) is determined by the formula:
Profiling Range = BD + (NC + 0.5) * CS
where:
BD = Blanking distance
NC = Number of cells
CS = Cell size
As mentioned earlier in the description of profiling range , bear in mind that while the ADP can
collect up to 100 cells of data, the system’s actual profiling range is restricted by other factors.
Averaging Interval
The averaging interval is the period of time, in seconds, over which the ADP averages data to
compute a mean velocity profile. For real-time applications, such as collecting river discharge
information, the averaging interval and
profiling interval are the same. This provides a continu-
ous measurement from start to finish.
The minimum value for this parameter is five seconds. For short distance transects, or transects
that will be traversed quickly (not recommended), typical values are from 5 to 10 seconds. For
long transects, or when several cells (i.e., number of cells is large) are used, typical values are
from 10 to 30 seconds.