Accounting for Under Ice Flow Angles in TRDI SxS Pro

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In this video, we will discuss the specifics of accounting for under ice 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: 00:02:14

Location Taken: Augusta, ME, US


Hi, my name is Nick Stasulis and I am a hydrologic technician with the Maine Office of the New England Water Science Center. In this video, we will discuss the specifics of accounting for under ice flow angles in the TRDI SxS Pro software.

For an under ice midsection ADCP measurement, the recommendation is to use the y-velocity method, which requires the ADCP be held at a fixed orientation to the cross section. With this method, flow angles are automatically computed by the software.

The correct orientation for the ADCP with the y-velocity method is to have beam 3 facing downstream, perpendicular to the tagline. Beam 3 is clearly marked on all TRDI ADCPs, including the RiverRay. This orientation must be maintained for the entire duration of each vertical. This requirement to have the ADCP aligned makes the rod and bracket you use to deploy the ADCP through the ice an important consideration. Ideally, your setup would be one that has an angle indicator on the rod that can be used when the ADCP is below the ice and can’t be seen. Also, you want a setup where the ADCP and the bracket holding it can’t spin on the rod. Ensuring your indicator is aligned properly with the ADCP is important too. Errors with deploying the ADCP due to the mount, rod and indicator on the rod are common sources of error with the y-velocity method. The user moving the ADCP during data collection or simply misaligning the ADCP when doing it by eye, are also common sources of error. During data collection, be sure to monitor the indicated angles after each station is collected and ensure they are reasonable.

If for some reason you held the ADCP with beam 3 at another alignment for all of the verticals, you can apply a beam 3 misalignment in the Processing dialog. This will be applied to all verticals, so if the alignment of beam 3 varied, this setting would not apply.

With the proper deployment setup and care during data collection, the use of y-velocity allows reliable flow angle correction for measurements under ice.