The Volume Scattering Function
The optical Volume Scattering Function (VSF) is an inherent optical property of water that is used by optical oceanographers to predict light propagation, image degradation, remote sensed ocean color, biological environment etc. in water.
Sequoia offers two instruments for this application. The LISST-200X and LISST-VSF. Respectively, these are for small-angle VSF and full-angle VSF with depolarization. Both measure beam attenuation.
The VSF can be thought of as composed of forward scattered (0-90°) and back scattered (90-180°) light, typically denoted bf and bb, respectively. Back scattering, bb, is of interest for scientists and practitioners concerned with ocean color studies and remote sensing. Sequoia offers the Hyper-bb for measuring bb for these applications.
Features
Small Angle VSF with the LISST-200X
The LISST-200X measures a weighted form of the VSF, covering the small forward range of angles, from 0.036 to 13.8° in water. No polarization information is available. The VSF measurements are offered at 32 log-spaced angles, i.e. successive angles increase by the factor 1.1809, beginning at the smallest values of 0.036°.
All measurements are made at the 670 nm wavelength of the laser. Measurements have been found to agree to within a few percent of Mie theory (see e.g. Agrawal (2005) in our library). Systems for the 532 nm green wavelength have been produced as custom units and remain available.
Wide Angle VSF with Polarization, using the LISST-VSF
The LISST-VSF is an instrument that combines the small-angle VSF capability of the LISST-100X with a wide angle capability, and with additional information on polarization properties of the scattered light.
Like the LISST-200X, the LISST-VSF measures the VSF at small angles, 0.1-15º with identical optics. Additionally, with a ‘roving eyeball’ optics design, it obtains a measure of the depolarization element P12. The roving eyeball covers the angles 15-160º in 1-degree intervals.
Hyper-spectral backscattering, bb, with the Hyper-bb
The Hyper-bb is a multispectral, self-contained submersible single-angle backscattering instrument with configurable spectral channels.
Specifications
It describes the angular dependence of the fraction of incident light that scatters into different directions:
Integrating the VSF from 0 to 180º yields the total scattering coefficient, b [m-1].
Integrating the VSF from 0 to 90º yields the forward scattering coefficient, bf [m-1].
Integrating the VSF from 90 to 180º yields the backscattering coefficient, bb [m-1].
The VSF is identical to the P11 element of the scattering Mueller matrix of water.
Sequoia offers 3 instruments that measure the VSF: The LISST-200X, the LISST-STOKES, and the LISST-VSF.
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