YSI SonTek RiverSurveyor, System Manual

Page: 156 / 194

SonTek/YSI Inc
RiverSurveyor System Manual (May 1, 2007)
144
The signal amplitude or SNR in the Contour or Profile Window is very low.
There are insufficient particles or “scatterers” in the water to return a good signal.
•
Select a different site for the measurement.
•
Use seeding material in the water. This may be difficult for long transects or in deep water.
The Contour Window is totally black.
The velocity reference (
Bottom-Track
,
GPS
) in use may not have any valid data.
•
If possible, select a different track reference. If the Contour Window remains black, the
other reference may also be invalid. You may need to repeat the measurement.
The Contour Window shows lots of gray areas.
Bottom-track has been lost several times during the transect.
Note : If you lose just a few bottom-tracks in your measurement section, RiverSurveyor
will take bottom-track data from the last good profile and use that data in computations
for the profile with the missing/invalid bottom-track information.
•
Ideally, you do not want to lose bottom-track at any time during the transect. If you have
lost bottom-track only a few times, your measurements may still be valid. If there is signifi-
cant loss of bottom-track across the section, it may be necessary to repeat the measurement.
The bottom (riverbed) is not displayed in the Contour Window.
The depth of water exceeds the maximum profiling range.
•
Increase the profiling range to the maximum depth for this site. See §
6.6.4
.
•
Cavitations (air entrained under the transducer head) may be occurring. Try lowering the
system in its mount or reducing vessel speed.
•
The system may have come out of the water.
9.7. Profile Window Conditions
One or more of the beams is very different from the others in the Profile Window.
Profiling close to a wall or obstruction may cause reflection of the acoustic beam.
•
Try to keep a significant distance away from structures (such as piles) and walls. A guide-
line is to keep the system a distance of at least ½ the water depth away from any structures.
•
Select a different section for your measurement.
•
Reduce the vessel speed over these areas to get better bottom depth resolution.
The Profile Window is showing unusual values for the signal amplitude.
Cavitations (air entrained under the transducer head) may be occurring; this is usually shown as
a straight line over the entire depth.
The system may have come out of the water.
There may be an obstruction or some debris lodged on the system.
There are insufficient particles or “scatterers” in the water to return a good signal.
•
Reduce the boat speed to limit the chance of cavitations occurring.
•
Move the ADP mount to a different location on the vessel.
•
Ensure the ADP transducers remain under the water at all times.