YSI SonTek RiverSurveyor, System Manual

Page: 33 / 194

SonTek/YSI Inc
RiverSurveyor System Manual (May 1, 2007)
21
3.2.3. What parameters are associated with current profiling?
For the amount and type of data collected by an ADP,
relatively few user-entered parameters are required. This
section briefly describes the major parameters associated
with current profiling. For a detailed description, refer to
ADP Principles of Operation in the
ADP Operation
Manual . The parameters described here include:
•
Profiling Range
•
Blanking Distance
•
Cell Size
•
Number of Cells
•
Averaging Interval
Profiling Range
The profiling range of an ADP is determined by user-
selected values for blanking distance, cell size, and num-
ber of cells (
Figure 3-9
). However, the actual profiling
range can be restricted by other factors:
•
System frequency (see
Table 3-1
)
•
Amount of scatterers in the water at the survey site
•
Interference from physical boundaries (surface,
bottom, objects in beam path)
Consider a 1.5-MHz ADP (which can collect data for up to 100 cells). If the maximum cell size
is used (4 m), it may appear that the system has a profiling range of 400 m. However, the maxi-
mum profiling range for this system frequency is
≈
25 m (see
Table 3-1
). RiverSurveyor systems
limit the maximum profiling range to a pre-defined maximum, so this is usually not a concern.
Blanking Distance
All ADPs have an area immediately in front of the transducers called the blanking distance
(commonly abbreviated as BD), where no measurements can be made. Data is not available in
this area because the transducers and electronic circuits need time to recover between the trans-
mit and receive cycles. That is, the blanking distance corresponds with the time it takes the ADP
to switch from transmitting its high-energy acoustic pulse through the transducer to being able to
receive through the same transducer the reflected signal from the scatterers in the water. The
blanking distance is user-selectable; the range of acceptable values varies based on system fre-
quency.
Table 3-1
lists the minimum values for the blanking distance parameter.
Figure 3-8. Example of Current Profiling
Figure 3-9. Parameters used to determine
ADP profiling range
BD
CS
NC
X
Y
Z
Vertical
profile
Depth cells