HydroBeta

HydroBeta is calibrated using a method similar to that for our single-angle backscattering sensor (details), and described in a paper published in Applied Optics.

Approach

HydroBeta with illuminated calibration target.  During calibration the target is moved along the path of the laser beam.


• Calibration is referred to a Spectralon? reflectance standard, not to fluids or microspheres.
  • The irradiance reflectance of the standard is known to be 99%.
  • The radiance reflectance as a function of angle, in water, is measured by HOBI Labs.
  • A second translucent standard (used for forward angles) is calibrated with reference to the solid standard.
• The response of each receiver to scattering throughout the laser beam is directly measured?not computed from optical approximations.
  • The target is placed in the path of the beam, and moved parallel to it.
  • The output of each receiver is measured as a function of the target's distance along the beam.
  • The resulting curves provide a complete and accurate description of the sensing geometry, which differs slightly for every channel.

Typical Response Curves (normalized)

Setup and Procedure

• The target is mounted on a rail such that it intersects the beam.
• A threaded rod allows the target position to be varied in precise increments.
• The angle of the target is adjusted on successive runs so that it can be viewed by the various receivers.
• For receivers at greater than 90° to the beam, a translucent target is used, and the beam scatters forward through it.