Examples of velocity spectra

The images below show different spectra as they are encountered in rivers and canals.

NOTE  

The colors are random and to not indicate the quality of the spectra.

Upward looking peaks refer to upstream measurements, downward looking peak to downstream measurements.

TIP  Click on images to enlarge!

  • One distinct peak
  • High intensity
  • Smooth
  • Negligible opposite direction

  • One distinct peak
  • High intensity
  • Smooth
  • Negligible opposite direction

  • One distinct peak
  • High intensity
  • Little noise
  • Negligible opposite direction

  • One distinct peak
  • High intensity
  • Little noise
  • Negligible opposite direction

  • Two little peaks
  • Small opposite direction

  • Two peaks

What you can do:

  • Change the sensor location
  • Reduce or increase the vertical mounting position
  • Align sensor parallel to flow direction
  • Increase the measurement duration

  • Peak with a tail

What you can do:

  • Reduce or increase the vertical mounting position
  • Change the sensor location
  • Increase the measurement duration
  • Align sensor parallel to flow direction

  • High opposite direction content
  • Noisy

What you can do:

  • Align sensor parallel to flow direction
  • Reduce or increase the vertical mounting position
  • Increase the measurement duration
  • Change the sensor location

  • Extreme noise

What you can do:

  • Place a chain, rope or other item upstream into the water to create additional waves
  • Increase the measurement duration
  • Switch Channel type to closed or vice versa

  • Very low velocity
  • Very low intensity

What you can do:

  • Place a chain, rope or other item upstream into the water to create additional waves
  • Increase the measurement duration
  • Switch Channel type to closed or vice versa

  • No peak
  • Very low intensity

What you can do:

  • Place a chain, rope or other item upstream into the water to create additional waves
  • Increase the measurement duration
  • Switch Channel type to closed or vice versa

  • Symmetric spectrum around zero at low velocities
  • High intensity

Reason

  • Glassy water surface with lake-like waves
  • RQ-30 measures vertical velocity

What you can do:

  • Place a chain, rope or other item upstream into the water to create additional waves
  • Change the sensor location