Haubrich, David (2010-08). Instrumentation to Measure the Backscattering Coefficient bb for Arbitrary Phase Functions. Doctoral Dissertation. Thesis uri icon

abstract

  • The backscattering coefficient bb is one of the inherent optical properties of natural waters which means that it is independent of the ambient light field in the water. As such, it plays a central role in many problems of optical oceanography and is used in the characterization of natural waters. Essentially, any measurement that involves sending a beam of light into water must account for all inherent backscattering. Some of the applications that rely on the precise knowledge of the backscattering coefficient include studies of suspended particle distributions, optical bathymetry, and remote sensing. Many sources contribute to the backscattering, among them any suspended particles, air bubbles, and the water molecules themselves. Due to the importance of precise measurements and the ease with which water samples can be contaminated, an instrument to determine directly and quickly the backscattering coefficient in situ is highly desirable. We present such an instrument in both theory and experiment. We explain the theory behind our instrument and based on measurements made in the laboratory we demonstrate that our prototype shows the predicted behavior. We present data for increased extinction in the water, and show how measuring the extinction and taking it into account improves the quality of our measurements. We present calibration data obtained from three different particle sizes representing differently shaped volume scattering functions. Based on these measurements we demonstrate that our prototype has the necessary resolution to measure the backscattering coefficient bb over the whole range found in natural waters. We discuss potential improvements that should be made for a commercial version of the instrument.
  • The backscattering coefficient bb is one of the inherent optical properties of natural
    waters which means that it is independent of the ambient light field in the water.
    As such, it plays a central role in many problems of optical oceanography and is used
    in the characterization of natural waters. Essentially, any measurement that involves
    sending a beam of light into water must account for all inherent backscattering. Some
    of the applications that rely on the precise knowledge of the backscattering coefficient
    include studies of suspended particle distributions, optical bathymetry, and remote
    sensing. Many sources contribute to the backscattering, among them any suspended
    particles, air bubbles, and the water molecules themselves. Due to the importance of
    precise measurements and the ease with which water samples can be contaminated,
    an instrument to determine directly and quickly the backscattering coefficient in situ
    is highly desirable.
    We present such an instrument in both theory and experiment. We explain the
    theory behind our instrument and based on measurements made in the laboratory
    we demonstrate that our prototype shows the predicted behavior. We present data
    for increased extinction in the water, and show how measuring the extinction and
    taking it into account improves the quality of our measurements. We present calibration
    data obtained from three different particle sizes representing differently shaped
    volume scattering functions. Based on these measurements we demonstrate that our
    prototype has the necessary resolution to measure the backscattering coefficient bb over the whole range found in natural waters. We discuss potential improvements
    that should be made for a commercial version of the instrument.

publication date

  • August 2010