CH Acoustic Doppler & Velocity Measurement

Question 1

What physical principle does an Acoustic Doppler Current Profiler (ADCP) use to measure water velocity?

Accepted Answer

Doppler frequency shift of acoustic pulses reflected by scatterers

Answer

Pressure differential across a Venturi constriction

Answer

Electromagnetic induction in a conducting fluid

Answer

Time-of-flight of laser pulses through water

Question 2

Which ADCP blanking distance parameter defines the zone nearest the transducer where velocity data cannot be reliably collected?

Accepted Answer

Blank before transmit

Answer

Bin size

Answer

Bottom-track range

Answer

Ensemble interval

Question 3

A moving-vessel ADCP discharge measurement uses bottom tracking primarily to:

Accepted Answer

Reference vessel velocity so water velocity can be isolated

Answer

Determine water temperature profiles

Answer

Calibrate salinity sensors

Answer

Map sediment grain size

Question 4

In an ADCP measurement, what does the term 'ensemble' refer to?

Accepted Answer

The average of multiple pings collected over a short interval

Answer

A single acoustic pulse

Answer

The full depth profile from surface to bed

Answer

The GPS position fix associated with one transect

Question 5

Which four-beam Janus transducer configuration is most commonly used in ADCP instruments to resolve three-dimensional velocity components?

Accepted Answer

Beams angled at 20° from vertical in opposing pairs

Answer

Beams angled at 45° and directed horizontally

Answer

Two vertical beams and two horizontal beams

Answer

A single rotating beam at 30° tilt

Question 6

When an ADCP operates in 'water mode 12' (WM12), it is optimized for measuring velocity in:

Accepted Answer

Shallow, fast-moving rivers with high turbulence

Answer

Deep ocean environments with strong stratification

Answer

Tidal estuaries with bidirectional flow

Answer

Lakes with very low backscatter