Accounting for Open Water Flow Angles in SonTek RSSL

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Detailed Description

In this video we will outline the process of accounting for open water flow angles in the SonTek RSSL software. Note: Use of trade names is for descriptive purposes only, and does not imply endorsement by the USGS. For additional videos in this series, visit the following link:


Date Taken:

Length: 00:01:57

Location Taken: Augusta, ME, US


Hi my name is Nick Stasulis and I work with the Maine Office of the New England Water Science Center. In this video we will outline the process of accounting for open water flow angles in the SonTek RSSL software.

For an open water measurement in RSSL, it’s recommended that you use the ENU coordinate system, which will use the ADCP’s compass and the azimuth of the tagline to compute the angle of the flow through your cross section. To do this, it’s recommended you calibrate the ADCP’s compass before the measurement. Compass calibrations are covered in the pre-measurement tests video at the link shown.

Once the ADCP’s compass is calibrated, you have to be sure the tagline azimuth is collected when setting up the measurement. This is done in the system settings by clicking Get Tagline Azimuth, which brings up this dialog. Be sure the ADCP is located away from anything that may affect the compass heading and at the orientation shown, with the connector downstream and perpendicular to the tagline. Click the start button and collect 10 to 20 seconds of data showing a stable reading, then click Stop. Once this is complete, close the dialog. It may be useful to obtain a tagline azimuth with a hand compass to confirm the azimuth reading from the ADCP.

Once the compass calibration and tagline azimuth are complete, simply ensure the ENU option is selected for each vertical. Be sure to note that even though the ADCP is accounting for angle automatically, you still need to monitor the flow angle reported for each station and ensure they are reasonable compared to your observations of the river. Sources of magnetic interference, such as steel bridge pilings, can result in erroneous flow angles. 

These flow angles are reported in the Samples page, allowing them to be easily compared from one station to the next.