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ADVM Site-Specific Programming

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### ADVM Site-Specific Programming

Streamflow Record Computation using ADVMs and Index Velocity Methods

Office of Surface Water

Measurement Volume

- Governed by:
- Velocity distribution
- Obstructions and boundaries
- Wake or flow disturbance
- Amount of “scatterers” in water
- Aspect ratio

Two Cell Sizes to Set

- If activate multi-cell profiling, 2 separate measurements:
- Overall, range-averaged cell
- Multi-cell

- Multi-cell data does not necessarily have to cover the same measurement volume as the range averaged cell

Step 1: Reconnaissance

Beam Check: TRDI ChannelMaster

Beam Check: SonTek Argonaut-SW

Step 3: Select Volume

- Cell Begin
- Cell End
- Blanking Distance - should be the same as cell begin
- Cell Size
- Number of Cells

Step 3a: Cell Begin/Blank

Wake Turbulence:

b = c(dx)0.5

b - lateral distance from pier centerline to edge of wake zone

d - pier width

x - distance to upstream face of pier

c - factor for pier shape

0.62 – round-nosed

0.81 – rectangular-nosed

x

d

b

ADVM

Step 3a: Cell Begin

- Review multi-cell data (once collected) to verify that the measurement volume is measuring in a region of undisturbed velocity
- Cell Begin:

Step 3b: Cell End

Cell End Marker

Cell Begin Marker

Theoretical Decay Curve

Instrument Noise Floor Marker

Step 3b: Cell End

- Avoid boundaries and obstructions
- Want beam amplitudes at least 10-20 counts above noise level
- Distance from a boundary is the greater of:
- 10% of the range
- Criteria based on ADVM frequency (SonTek):

Steb 3b: Cell End – Aspect Ratio Guidelines

- Aspect ratio (AR) = R/D, where
- R = range; end of the measurement volume
- D = distance to nearest boundary (surface, bottom, obstruction)

- Determines how far out you should profile to avoid beams or sidelobes glancing off water surface or streambed
- Maximum AR of 15-20 is recommended!
- Assumes sidelooker is installed perfectly level
- Under certain conditions it is possible to accurately measure at distances corresponding to AR > 20
- Must also avoid any other obstructions!

Aspect Ratio

- If max AR is 20, what is the max range we should measure?
- Range = 20 * 3 ft = 60 ft
- If the water level drops to 1 ft above the ADVM, what is the maximum range we should measure?
- Range = 20 * 1 ft = 20 ft

Sidelobe

4 ft

3 ft

Sidelobe

Measurement Range

Step 3b: Cell End

- Also review multicell data (once collected) to verify that measurement volume is measuring a region of undisturbed velocity
- Cell end:

Step 3c: Multi-cell

- Blanking distance (same as cell begin)
- Number of cells
- Cell size must be divided equally

If measurement volume = 10 m

Cell size = 10 m/10 cells = 1 m

Example

500 kHz ADVM to be mounted on left bank

Example, cont.

Flow

- Rock upstream of mount near ADVM
- Could cause undesirable turbulence near cell begin

Rock

Example, cont.

- Cell begin and blank:
Wake turbulence due to rock

- Computed minimum Cell Beginusing:
- b = c(dx)0.5, where
- c, shape factor = 0.62 (round rock)
- d, width of rock = 2 m
- x, distance from ADVM to upstream face of rock = 2.2 m

- Min Cell Begin: b = 0.62(2 * 2.2)0.5; b = 1.3 m
- Rounded up to 2 m to be conservative

Example, cont. (Cell begin & blank)

- Obstruction at 65 m
- Pick larger of:
- 10% * range to obstruction = 6.5 m
- 1.0 m (for 500kHz)
- 6.5 m

- Max cell end = 65 m – 6.5 m = 58.5 m

Example, cont. (Cell End)

- Check aspect ratio limitation
- Current cell end at 58.5 m
- ADVM axis to surface = ~2m
- ADVM axis to bed = ~2m
- If Max AR is 20, is a cell end of 58.5 m ok?

- Recompute:
- AR=58.5/2=29.2 – Too High!
- Re-arrange equation (AR = R/D) to calculate max cell end
- R=AR*D = 20*2 = 40 m max

Current Range = 58.5 m

2 m

2 m

Example, cont. (Cell End)

- Are beam amplitudes >10-20 counts above noise at 40 m?
- Yes

- Need to check in range of conditions!

>10-20 counts?

Example, cont.

- Cell begin/blank = 2 m
- Cell end = 40 m
- Measurement volume = 40 – 2 = 38 m
- Are we measuring in an appropriate velocity zone?
- Yes, appears so

- Multi-cell:
- SonTek, so 10 cells max
- Cell size = 38 m / 10 cells = 3.8 m each

Example, cont.

Individual Cells: Blank = 2 m

10 cells at 3.8 m each

500 kHz ADVM

Cell End = 40 m

Cell Begin = 2 m

Range-averaged Measurement Volume = 38 m

Changing Scatterers

- Be careful! Amount of scattering material may change over seasons. Measurement volume may change.

Changing Scatterers, cont.

- Cell End changes during a 2-month period

Measurement Volume for Uplookers

- Range-averaged cell end is pulled back automatically
- “Dynamic Boundary Adjustment”
- However, multi-cell locations are fixed!

SonTek SW and XR

- Dynamic boundary adjustment –
- Activated only in single depth-averaged cell!!
- SW uses acoustic stage to set cell end
- XR uses pressure sensor to set cell end

- Multi-cell option has a fixed range or cell end – be careful! Near-surface cells can be corrupted/biased if water level falls below the last one or more cells

60 s

Averaging Interval and Measurement Interval- Averaging Period or Interval (AI) The interval over which velocity measurements are collected, from which a mean velocity is reported
- Measurement or Sampling Interval (SI) How often we record velocity (unit value interval)
- The sampling interval can be set either in instrument or datalogger. In SDI-12 mode, the datalogger dictates the sampling interval!!

S.I.

A.I. = 15 sec

S.I. = 30 sec

A.I.

ping

15 s

Time

Averaging Interval - Unsteady Flow

- SI = 15 min.
- AI = 13.5 min.
- ADVM is collecting data most of the time
- Configuration is good for computing average flow, but extremes may not be measured well

48-minute period

Averaging Period

- Smoothing the data for routine data collection
- 1 min. to 10 min. averaging period

Averaging Interval – Advantages of Short AI

- Reduced power consumption
- Effect of a bias might be more evident than for long AIs. For example, if the ADVM beams hit a barge passing by or measure the wake of a ship
- Short-term flow variations are captured

Averaging and Measurement Considerations

- AI <= SI
- Leave some buffer time for SDI-12; approximately 1 min.
- Telemetry
- Number of parameters transmitted may be limited

Averaging and Measurement Considerations

- Will likely have 3 time periods with different sampling intervals and averaging intervals:
- Initial exploratory measurements (when ADVM first installed)
- Routine data collection (after exploratory period)
- During discharge measurements (to improve synchronization of data)

Recommendations – Exploratory Period

- Perhaps start with:
- 5 minute (300 seconds) measurement interval
- 4 minute (240 seconds) averaging period
- Also measure stage every 5 minutes
- This will give you 12 measurements per hour
- Can adjust these if needed after reviewing data

Recommendations – Routine Data Collection

- The sampling interval that correctly represents changes in flow over hydrograph is called the “Nyquist sampling rate”
- Example: if streamflow changes from base flow to peak flow in 10 minutes, then we want a maximum sampling interval = 10/2 = 5 minutes
- Maximum measurement interval = 15 minutes
- Especially for tidal sites

- Recommendations:

Recommendations – During Discharge Measurements

- Change to 1-minute sampling intervals and averaging intervals during flow measurements
- Velocity data
- Stage data if practical

- Allows for accurate synchronization with measurements
- Make sure ADCP, ADVM, and DCP clocks are synced prior to the measurement!!

Correct Time:

www.time.gov

http://tf.nist.gov/

Aliased Data – Class Question

- Qm start = 13:00:00
- Qm end = 13:11:33
- Mid-time = 13:05:46
- If sampling interval was 15 minutes, what would be the index velocity (roughly)?
- If sampling interval was 1 minute, what would be the index velocity?
- The 15-minute index would be substantially less and could introduce error into rating!!

Salinity

- Salinity is a measure of the dissolved salt content in water
- Important because it affects density & speed of sound
- Needs to be measured & configured in the ADVM
- Most ADVMs allow entry of only 1 value
- Change in salinity of 0 to 35 ppt results in 3% change in velocity
- If salinity is significant and varies, enter the mid-point of the salinity range
- Some sensors output conductivity, which is related to salinity. Online calculators at:
- http://www.fivecreeks.org/monitor/sal.shtml and
- http://www.chemiasoft.com/salinitycalc.html

Courtesy YSI

Coordinate Systems

- Typically set to XYZ or instrument to prevent compass errors from being introduced to data
- If need earth coordinates (ENU), be sure to calibrate compass and remove all ferrous materials from mount and area!!

Stored and Transmitted Parameters

- Recommended, parameters (in order):
- X velocity
- Water temperature
- Cell End
- Y velocity
- Z velocity (if applicable)
- Signal amplitude or SNR
- Multi-cell data if needed
- 5 cells max for SonTeks
- 20 cells max for TRDIs

Make sure internal ADVM record is on, too!

SonTek-Specific Programming

- Unit System (Metric/English)
- PowerPing (turn on if available)
- Temperature (set to MEASURED)
- ReverseXVelocity (for Sidelookers, if needed)
- Deployment
- Name of internal recorder file
- Start date and time of measurements

Enable PowerPing in SonTeks

SonTek ReverseXVelocity

- By default, ADVM thinks that it is mounted on the right bank
- Arrow on ADVM face shows the assumed primary flow direction
- If mount on opposite bank, velocities in downstream direction will be reported as negative
- Turn ReverseXVelocity to “Yes” if you want those velocities reported as positive

TRDI Reverse X Velocity

- The TRDI Channelmaster has a checkbox and field for bank configuration

SonTek-Specific Programming

Documentation

- Document all installation parameters and configuration settings
- Use form in Appendix 2 of T&M Report
- Also posted at: http://hydroacoustics.usgs.gov/indexvelocity/techtips.shtml
- Store a configuration log file when programming ADVM

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