LISST-STOKES - Submersible Instrument for Measuring The Depolarization Ratio In Situ
The LISST-STOKES from Sequoia is the world’s first commercially available submersible instrument for measuring the depolarization ratio in situ. Temperature and depth is included for each measurement. Also the beam attenuation at the two wavelengths is included with each measurement. Power is applied externally, either via an external power cable or an external battery pack (included). Data processing is performed using MATLAB scripts, which are supplied open-source and free of charge with the instrument to the user. No Windows software exists or will be supplied for the LISST-STOKES; the user MUST have MATLAB and be proficient in its use to process LISST-STOKES data.
Although the LISST-STOKES is designed for use in situ and can be submerged to a depth of 300 m, it can also be used in a laboratory setting for measuring discrete samples. The measurement frequency is one measurement every 27 seconds. For this reason, the LISST-STOKES is not suitable for continuous profiling applications, except in circumstances where the profiling is done in steps, holding the instrument at a constant depth for at least 27 seconds.
This is accomplished using two independently switched, linearly polarized, fiber-coupled lasers. A 45° beam splitter divides the scattered light in two paths; one part scatters onto a custom 32-angle ring detector from where the VSF is obtained. The other part of the light passes through an analyzer and is detected by a CCD array. From this measurement the depolarization ratio is obtained. In addition to the depolarization ratio, the VSF is obtained at 2 wavelengths; red (658 nm) and green (532 nm). The angular range covered by the ring detector is 0.752 – 148 mrad IN WATER.