YSI SonTek RiverSurveyor, System Manual

Page: 61 / 194

SonTek/YSI Inc
RiverSurveyor System Manual (May 1, 2007)
49
Always consider the difference between bottom-track and GPS, and their methods of calculating
vessel position, when processing your velocity and positional data. As mentioned previously,
bottom-track is a “relative position” system and GPS is an “absolute position” system.
By default, the track and velocity references are not linked. However, the U.S. Geological Sur-
vey recommends maintaining the same track and velocity reference at all times. An option in the
Program
Configuration can force the track and velocity reference to be consistent at all times.
3.10.6. What does Depth Reference mean?
Depth reference refers to the source of the input that will be used to calculate the depth of water
at any time. There are two depth references available:
•
Bottom-Track [default setting] – available on all RiverSurveyor systems (§
3.3
).
•
Echo Sounder – available only if connected to your system via an additional COM port on
your computer (§
3.5
).
3.10.7. How will selecting a different Depth Reference change my results?
In most cases, there will be minimal differences between selecting either bottom-track or the
echo sounder as the depth reference. There are times when it may be advantageous to use the
echo sounder for depth measurements, such as when there is a high concentration of suspended
sediments or when the bottom of the river is not clearly defined (§
3.3.5
; Moving Bed).
One of the benefits of using RiverSurveyor is that the depth reference can be changed at
any time during post-processing, or when the system is not collecting data, by clicking
Use Echo Sounder for depth measurements
on the
Processing
toolbar. Additionally, RiverSur-
veyor can be configured to always use the echo sounder depth when profile depths are lost due to
invalid bottom-track.
3.11. Shallow Water Operation
The following topics are covered in this section:
•
What is Shallow Water Operation?
•
How does Shallow Water Operation work with RiverSurveyor?
•
Where should I use Shallow Water Operation with RiverSurveyor?
3.11.1. What is Shallow Water Operation?
This feature allows you to collect additional ve-
locity data when operating in shallow water. Wa-
ter velocities in a “shallow water” cell are meas-
ured and added to the top of the standard velocity
profile (
Figure 3-24
). The flow and depth condi-
tions determine the validity of the cell. Result: A
greater percentage of the total water throughout
the cross-section is measured.
This feature is available on both the 1.5-MHz and
3.0-MHz RiverSurveyor ADPs. This means that
velocity data can be collected in water as shallow
as 0.5 m and 0.3 m, respectively.
Figure 3-24. Display of Shallow-Water Cell