YSI SonTek RiverSurveyor, System Manual

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SonTek/YSI Inc
RiverSurveyor System Manual (May 1, 2007)
32
•
The antenna should have a clear, unobstructed “view” of the sky. Avoid measurement areas
close to bridges, tree canopies, and steep canyons that can obstruct the GPS signal or cause
it to reflect off an obstruction before being received by the GPS unit. GPS reflections
(called
multi-path errors ) significantly degrade GPS performance and cause major errors in
discharge values. These types of errors cannot be corrected in post-processing.
•
Make sure your GPS receiver unit is using the appropriate communications settings. Typical
serial communication settings for a GPS unit are:
- Baud rate – 4800
- Data bits – 8
- Stop bits – 1
•
RiverSurveyor is designed to handle a variety of incoming GPS strings; however, the speed
of the connection will limit the data transfer rate. If possible, set up the GPS receiver unit to
output only the string necessary for making a measurement (e.g., “GGA”; §
3.4.4
).
•
Magnetic declination adjustments always need to be made when using GPS as a reference.
You will need to determine the magnetic declination value for the site being surveyed.
Many times this value can be found near the compass rose of high-quality survey maps or
determined from software programs designed to compute this value based on latitude, longi-
tude, and date (see
Glossary listing for details).
GPS Settings
After resolving the issues described above, you can connect your GPS serial cable to your com-
puter. Remember which serial port you use, as you will need this information in the
RiverSur-
veyor program.
The GPS input into RiverSurveyor is set up via the
Systems
dialog box (
Figure 3-13
). The
Sys-
tems
dialog box can be displayed by selecting
Communications|Systems
or by clicking the
Sys-
tems
icon on the toolbar. See §
7.3.3
for an overview of the
Systems
dialog box.
The
Systems
dialog box shows two sources of GPS information, although only one can be se-
lected at any time:
•
External GPS
– This system is used when GPS input is through a computer serial port. You
must ensure the correct communication settings for the GPS serial port selected.
•
Internal GPS
– This is only available for systems that have the internal GPS option enabled
(e.g., RiverCat systems). It only becomes active when an ADP with Internal GPS is selected
and when successful communications is established.
Figure 3-13. Systems dialog box in RiverSurveyor (External/Internal GPS)