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ADVM Site-Specific Programming. Streamflow Record Computation using ADVMs and Index Velocity Methods Office of Surface Water. Overview. Terminology. Terminology. Terminology. Measurement Volume and Multi-cell. Measurement Volume. Governed by: Velocity distribution

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Advm site specific programming

ADVM Site-Specific Programming

Streamflow Record Computation using ADVMs and Index Velocity Methods

Office of Surface Water







Measurement volume
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
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
Step 1: Reconnaissance



Beam check trdi channelmaster
Beam Check: TRDI ChannelMaster


Beam check sontek argonaut sw
Beam Check: SonTek Argonaut-SW


Step 3 select volume
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

Flow

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
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
Step 3b: Cell End

Cell End Marker

Cell Begin Marker

Theoretical Decay Curve

Instrument Noise Floor Marker


Step 3b cell end1
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
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
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 end2
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
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
Example

500 kHz ADVM to be mounted on left bank


Example cont
Example, cont.

Follows decay curve fairly well

Obstruction at ~ 65 m

> 10-20 counts?


Example cont1
Example, cont.

Flow

  • Rock upstream of mount near ADVM

  • Could cause undesirable turbulence near cell begin

Rock


Example cont2
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
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
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 end1
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 cont3
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 cont4
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
Changing Scatterers

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


Changing scatterers cont
Changing Scatterers, cont.

  • Cell End changes during a 2-month period


Measurement volume for uplookers
Measurement Volume for Uplookers

  • Range-averaged cell end is pulled back automatically

  • “Dynamic Boundary Adjustment”

  • However, multi-cell locations are fixed!


Dynamic boundary adjustment
Dynamic Boundary Adjustment

Example for SonTek XR

Reprinted from SonTekweb site. www.sontek.com


Sontek sw and xr
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



Averaging interval and measurement interval

30 s

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
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
Averaging Period

  • Smoothing the data for routine data collection

  • 1 min. to 10 min. averaging period


Averaging interval advantages of short ai
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
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 considerations1
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
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
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
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
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

  • 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
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
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
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



Sontek reversexvelocity
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
TRDI Reverse X Velocity

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




Sontek specific programming1
SonTek-Specific Programming


Documentation
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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