Sequoia Scientific - Model LISST-VSF -Submersible Instrument for Measuring The Volume Scattering Function

• In-situ measurements of P11, P12 and P22 (noisy) elements of scattering Mueller matrix, (P11 is VSF) from 15-150º (no P22 estimate at 45 and 135°).
• VSF (P11) only at small angles, 0.09 to 10º in 32 logarithmic steps in angles.
• Only two detectors employed with absolute radiant sensitivity (A/W) calibration.
• Beam attenuation measured with optics similar to our LISST-100X/200X.
• Roving Eyeball™ optics permit 1-degree resolution in angles between 15 -150º.
• Sampling rate at 4 seconds per measurement set (involves 2 turns of Roving Eyeball with vertical, and horizontal laser polarization).
• Daylight rejection by laser modulation.
• Dynamic range in VSF measurements extended via laser power dimming.
• Data from small and large angles in a single data stream, including depth and temperature.

The LISST-VSF comes with all the items necessary for deployment including a rechargeable NiMH external battery pack that allows more than 15 hours of continuous data collection. A test chamber is also provided to allow the instrument to be tested in the lab. An optional mixed test chamber with four counter rotating mixers is available for extensive laboratory testing.

The LISST-VSF also ships with Matlab scripts that allow for both viewing raw data and for one step data processing. Raw data from the instrument is plotted using a Matlab based GUI. This piece of software is useful for conducting quick QC checks of the data or ensuring cleanliness of the instrument and/or background water.

The Matlab processing functions handle all of the calculations required to convert raw data to the calibrated Volume Scattering Function. All that is required for processing is a raw data file and a clean water background file. The processing function returns approximately 15 different computed variables, most notably:

• P11 (Volume Scattering Function)
• P12
• Noisy estimate of P22, and no P22 estimate at 45 and 135°
• Beam attenuation coefficient (c)
• Scattering coefficient (b)
• Depth
• Temperature

The processing function also provides the option of plotting several of the computed data products.

All of the source code for the processing functions ship with the LISST-VSF. The code can be edited for custom applications or used as a tool to better understand the steps involved in the data processing.

See article below for more details about the LISST-VSF or click here to read the abstract.

Slade, W.H., Agrawal, Y.C. and Mikkelsen, O.A., 2013, September. Comparison of measured and theoretical scattering and polarization properties of narrow size range irregular sediment particles. In Oceans-San Diego, 2013 (pp. 1-6). IEEE.  Link to Full Text

Parameters Measured

• Small-angle VSF in 32 log-spaced angles, from 0.05 to 10º.
• VSF, P12 and P22 over 15-150º  in 1º steps.
• Temperature from –5º to 50ºC @ 0.1ºC resolution.
• Depth (300 m max) @ 10 cm resolution

Operating Concentration Range

• Beam attenuation from 0.2 to 20 m -1

Technology

• Doubled-YAG laser @ 532 nm.
• Ring Detectors for small-angle VSF.
• Roving Eyeball and PMT at 15-150º.

Mechanical and Electrical

• Dimensions: 12.7 cm × 114.3 cm (5.0″ × 45.0″) [Ø × L]
• Weight: 15.6 kg (34.4 lbs) in air; xx kg (x lbs) in water
• 300 m depth rating
• 128 GB internal solid state drive; equivalent to 24,000 measurements
• External power input: 12VDC nominal @ 5A (yes, FIVE amps), 9-20VDC
• Power drain: xxµA / 20mA / xxmA / 4,500mA (sleeping / idling / laser on / roving)
• Weight of EXTERNAL battery case xx kg (xx lbs) in air.