YSI SonTek RiverSurveyor, System Manual

Page: 95 / 194

SonTek/YSI Inc
RiverSurveyor System Manual (May 1, 2007)
83
6.6.3. Averaging Interval
The
Averaging Interval
(
Figure 6-4
) is the period of time, in seconds, over which the ADP aver-
ages data to compute a mean velocity profile. For RiverSurveyor applications, the averaging in-
terval and profiling interval are the same. This provides a continuous measurement across the en-
tire transect, from start to finish. The averaging interval must be a value from 5 to 43,200 sec-
onds (12 hours). However, most RiverSurveyor applications use values from 5 to 30 seconds.
Suggestions:
•
For short-distance transects (less than 1 km) or quickly traversed transects , we recom-
mend a value from 5 to 10 seconds.
•
For long-distance transects (greater than 1 km) or fast boat speeds , we recommend a
value from 10 to 30 seconds.
6.6.4. Magnetic Declination
Set the
Magnetic Declination
field to the appropriate value for your region via the
User Setup
dia-
log box (
Figure 6-4
;
ADP Configuration|User Setup
). For more information on magnetic declina-
tion , refer to §
3.8
. This field can be modified during post-processing.
If you are using a GPS unit through a serial connection that outputs the
RMC
string, you can auto-
matically set the magnetic declination for your region. Follow the instructions for
GPS Input
(§
3.4.6
). After you have verified the incoming GPS data stream for correctness, click
Get Mag-
netic Declination
to set the magnetic declination automatically.
6.6.5. Water Salinity
The
Water Salinity
value (
Figure 6-4
) is used in the calculation of the speed of sound. A value
representative of the local water conditions must be entered manually.
6.6.6. Transducer Depth/Mounting Depth
The depth of the transducer below the waterline is an important consideration when mounting
your system. While it is critical that the transducer head remain submerged at all times during
the measurement, it is also important to minimize the amount of unmeasured water near the sur-
face. Section
6.2
has information on mounting the ADP to a vessel. As for entering the depth of
the transducers via the
User Setup
dialog box (
Figure 6-4
;
ADP Configuration|User Setup
):
•
If your system does not have the Automatic Transducer-Mounting Depth Sensor (§
3.6
) op-
tion installed, you must manually measure the depth of the transducer head below the sur-
face of the water. You will then need to enter this value as the
Mounting Transducer Depth
.
This field can be modified during post-processing. Keep in mind that transducer depth er-
rors will systematically bias data high or low. If you are transecting a wide and shallow
cross-section, this could be significant. If the section is narrow and deep, errors would be
much smaller. It is also a good idea to check the sensor depth if there is a change in boat
personnel, which could result in a shallower or deeper setting.
•
If your system does have the Automatic Transducer-Mounting Depth Sensor (§
3.6
) option
installed, set
Transducer Depth Method
to
Automatic
, and then click the
Set
button and fol-
low the instructions. It is also a good idea to check the sensor depth if there is a change in
boat personnel/equipment, which could result in a shallower or deeper setting. For more in-
formation on ATMDS usage in RiverSurveyor, see §
3.6.4
.