1 / 58

ADVM Site-Specific Programming

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

mayda
Download Presentation

ADVM Site-Specific Programming

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ADVM Site-Specific Programming Streamflow Record Computation using ADVMs and Index Velocity Methods Office of Surface Water

  2. Overview

  3. Terminology

  4. Terminology

  5. Terminology

  6. Measurement Volume and Multi-cell

  7. Measurement Volume • Governed by: • Velocity distribution • Obstructions and boundaries • Wake or flow disturbance • Amount of “scatterers” in water • Aspect ratio

  8. 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

  9. Step 1: Reconnaissance

  10. Step 2: Beam Check

  11. Beam Check: TRDI ChannelMaster

  12. Beam Check: SonTek Argonaut-SW

  13. Step 3: Select Volume • Cell Begin • Cell End • Blanking Distance - should be the same as cell begin • Cell Size • Number of Cells

  14. 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

  15. 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:

  16. Step 3b: Cell End Cell End Marker Cell Begin Marker Theoretical Decay Curve Instrument Noise Floor Marker

  17. 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):

  18. 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!

  19. 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

  20. Step 3b: Cell End • Also review multicell data (once collected) to verify that measurement volume is measuring a region of undisturbed velocity • Cell end:

  21. 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

  22. Example 500 kHz ADVM to be mounted on left bank

  23. Example, cont. Follows decay curve fairly well Obstruction at ~ 65 m > 10-20 counts?

  24. Example, cont. Flow • Rock upstream of mount near ADVM • Could cause undesirable turbulence near cell begin Rock

  25. 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

  26. 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

  27. 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

  28. 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?

  29. 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

  30. 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

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

  32. Changing Scatterers, cont. • Cell End changes during a 2-month period

  33. Measurement Volume for Uplookers • Range-averaged cell end is pulled back automatically • “Dynamic Boundary Adjustment” • However, multi-cell locations are fixed!

  34. Dynamic Boundary Adjustment Example for SonTek XR Reprinted from SonTekweb site. www.sontek.com

  35. 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

  36. BREAK

  37. 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

  38. 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

  39. Averaging Period • Smoothing the data for routine data collection • 1 min. to 10 min. averaging period

  40. 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

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

  42. 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)

  43. 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

  44. 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:

  45. 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/

  46. 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!!

  47. 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

  48. 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!!

  49. 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!

  50. 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

More Related