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Known Issues

The Office of Surface Water has compiled a list of issues associated with hydroacoustic instruments in use in the Water Mission Area. The items listed below are the major issues that OSW is working to resolve. The intent of this list is to assist hydrographers using ADCPs, ADVs, and ADVMs by sharing these issues, the status of work on the issues, and any potential work-arounds. This list will be updated regularly.

Teledyne OceanScience Q-Boat

Issue	Status	Solutions
Electromagnetic Interference The vessel control unit (VCU) of older Q-Boats can cause electromagnetic interference with TRDI ADCPs. Newer VCUs do not have the issue. New VCUs have heat fins on the back and part number 70L-2003-00. To test whether the VCU causes electromagnetic interference, run the ADCP test with and without the remote boat running and compare the results of the PT3 test. QRev highlights the issue if PT3 test results are bad.	The solution has been tested with three Q-boats and shown to work in all cases. Resolved.	The solution is to install a new board supplied by TRDI to the vessel control unit. The first step in replacing the board is to send a picture of the inside of the VCU to TRDI and then follow up with them.

SonTek SL-3G

Issue	Status	Solutions
Incorrect Velocity Data If the SL Vertical Beam fails to acquire a signal indicating a reasonable water surface (acoustic path blocked or other issues) the cell end for the integrated velocity cell is pulled way back. Multicell data in software appear erroneous, but the data are still available in the raw output/internal recorder file.	Issue in versions prior to 3.0. Firmware Version 3.0 released 6/6/2018 resolves this issue.	Upgrade firmware to version 3.0.

SonTek iQ Plus

Issue	Status	Solutions
SDI-12 and Reprogramming If an SDI-12 command is issued at the same time as an attempt to reprogram AI/SI and output, the changes may fail to write to the ADVM as the unit has begun an SDI driven sample.	Issue reported to SonTek.	The suggested workaround is removing the SDI-12 line from the DCP when reprogramming the unit. Alternatively, you can reopen the software, following changes, and verify the updated configuration is present; however, the problem could still occur if timing is not correct.
Bias in Computed Discharges Testing by USGS HIF in the Hydraulics Lab and field comparisons by Colorado Division of Water Resources have indicated that computed discharges may be biased low in some channels and situations.	No additional testing is planned.	The iQ Plus discharge computation feature is not used in the USGS. Additional tests by the HIF shown that a previously-detected velocity bias is much reduced with firmware 1.60. The iQ Plus should be suitable for application of the index velocity method (Levesque and Oberg, 2012) if firmware version 1.60 or later is installed.

Teledyne RD Instruments WinRiver II

Issue	Status	Solutions
Compass Evaluation Not Stored Rio Grande compass evaluation is not stored if the "Close" button is pressed after total error reported but before the "Evaluate" and "Calibrate" buttons are re-enabled.	Present in WRII v. 2.18 and earlier. Version 2.20 has not been tested sufficiently to know if this issue has been addressed.	Wait until the "evaluate" and "calibrate" buttons are re-enabled before closing.
"Negative" SMBT Results Not Used When multiple stationary moving bed tests (SMBTs) are completed, checked, and some SMBTs indicate a moving bed correction is needed, any SMBT that has slightly negative (downstream) motion will not be used in determining the proportional correction.	Fixed in version 2.20	If multiple stationary MBTs are required for a correction, attempt to collect any tests where no moving bed is detected and the SMBT result is not negative and a near-zero moving-bed velocity will be used to determine the moving bed correction.
SMBT Application Not Recommended When using the SMBA corrections, a correction will be applied if the moving bed test is checked, even if slight there is upstream boat motion for the SMBT.	Present in WRII v. 2.10 and later	Uncheck all moving bed tests when no correction is warranted; ie. moving bed velocity is < 1% of mean flow speed.

Teledyne RD Instruments RiverPro / RioPro

Issue	Status	Solutions
RioPro Blanking Distance The default blanking distance for the RioPro is 10 cm. Given that the diameter of the RioPro is unchanged from the Rio Grande ADCP, the blanking distance probably ought to be 25 cm in order to minimize bias in measured velocity caused by flow disturbance (Mueller and others, 2007). RioPro (and RiverPro) firmware adjusts the blanking distance automatically to account for backscattering conditions and their effect on ringing.	Reported to TRDI. Change to default blanking distance is not possible. USGS has addressed this issue by automatically appling an "Excluded Distance" in QRev for all RioPro measurements.	Use QRev to process RioPro measurements.
Depth Reference For RiverPro ADCPs equipped with a vertical beam, discharges computed using the vertical beam as a reference tend to be less than discharges computed using the 4-beam average.	Vertical beam improved in Firmware 56.06	Use of the vertical beam is acceptable. However, nearly all historical comparison data validating the use of ADCPs have been based on the 4-beam average depth.

Teledyne RD Instruments RiverRay

Issue	Status	Solutions
Low-backscatter Bias Prior to firmware version 44.13, RiverRay discharges were biased low when the backscatter was low (< 70 dB).	Issue fixed in Firmware 44.19	If the discharge measured using a RiverRay is unexpectedly less than the expected discharge during low backscatter conditions: (1) make a comparison measurement with another instrument, and (2) report results to OSW.
Depth Reference For RiverRay and RiverPro ADCPs equipped with a vertical beam, discharges computed using the vertical beam as a reference tend to be less than discharges computed using the 4-beam average.	Vertical beam improved in Firmware 44.21.	Use of the vertical beam is acceptable. However, nearly all historical comparison data validating the use of ADCPs have been based on the 4-beam average depth.

Teledyne RD Instruments StreamPro

Issue	Status	Solutions
Acoustic/Electromagnetic Interference Some StreamPro measurements are susceptible to interference. Identified by examination of the PT3 test and by increases in correlation or vertical velocity with depth.	QRev evaluates and warns user of potential EMI issues.	No known solution. Use another instrument. Because the issue is site dependent and evidence suggests that it is constant in time, use of the StreamPro at these locations is not recommended.