Accounting for Open Water Flow Angles in TRDI SxS Pro

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In this video, we will discuss the specifics of accounting for open water flow angles in the TRDI SxS Pro 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: 00:02:13

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 discuss the specifics of accounting for open water flow angles in the TRDI SxS Pro software.

For an open water midsection ADCP measurement, the recommendation is to use the magnitude velocity method, where the magnitude of the mean velocity is used to compute flow for a particular vertical. With this method, you must enter the flow angle through the cross section for each vertical, if it is not perpendicular. This is essentially the same as what is done for traditional AA or pygmy current meter measurements.

Due to the requirement for manually measuring flow angle, the ADCP must be deployed in a way that allows the user to easily measure this flow angle. For example, from a manned cableway or bridge. If the ADCP is deployed in a way that the user is limited to the shore, like a bank operated cableway, measuring the flow angle is not very practical.

We assume the alignment of the boat is approximately equal to the mean flow direction. To measure the flow angle, it is recommended that a protractor, paper measurement form, angle indicator or other similar device is used. Simply making a best guess by eye is not appropriate, an angle measurement device should be used. Most devices allow one straight edge to be aligned with the tagline and the ADCP or water surface used to determine the angle. If you use the ADCP, be sure it’s relatively stable as a swimming ADCP could make it hard to measure an accurate angle.

Once the angle is determined, which must be done before you start data collection at a vertical, enter either the angle in degrees or the coefficient into the dialog for the vertical you are about to collect. Notice that you don’t need to enter both fields, entering one will populate the other.

During playback, if you realize an angle was entered in error, you can simply double click any vertical in the contour view or the verticals detail page to edit the entry.