LISST-
Tau User’s Manual
Introduction and Tutorial
Page 1
I.
Introduction and Tutorial
A.
General Description
Instrument
Description
The LISST-Tau measures the transmission (and inversely, attenuation)
of light in water, at a single narrow wavelength range centered on either
532 or 650 nm. Its rugged aluminum housing and high-resolution digital
electronics provide outstanding measurement quality in any in-situ
application at depths up to 2000 meters.
LISST-Tau generates a beam of light from an LED, formed by a lens
into a uniform, low-divergence beam. The LED is modulated at 1000
Hz. 532-nm LISST-Tau models also have a spectral filter to control the
spectral bandwidth. A beam splitter and reference detector measure
the beam intensity before it enters the water. On the receiver side, a
lens and pinhole capture all the light arriving at angles less than 1.0
degree. The receiver electronics sample the incoming light at 1000 Hz,
synchronously with the modulation of the LED source, rejecting light
from solar background or other sources.
A digital controller receives the digitized signals and applies appropriate
calibration factors to generate the final transmission and attenuation
values. The processing includes applying corrections for the small
residual effects of temperature on the measurements. Factory
calibration of every LISST-Tau includes measuring its response across
the full temperature range.
The controller transmits digital data, once per second, via its RS-232
serial interface at 19200 baud. The digital data stream includes
calibrated, temperature-corrected transmission and beam attenuation,
as well as raw signal values, temperature, etc. LISST-Tau also
produces an analog voltage proportional to transmission, for
compatibility with any analog-input CTD or logging system.
Included
Accessories
The LISST-Tau is shipped pre-calibrated and tested in a Pelican ship
case. Included with the instrument are a USB power and
communication cable, instrument stands,
User’s Manual and USB card
with software. The supplied USB cable provides both power and
communication for the LISST-Tau, when used with any PC or tablet
running Microsoft Windows.
The LISST-Tau Windows application communicates with the
instrument, displays and records data, and allows simple checking of
operation before deployment. The software provides real-time display
of transmission or beam attenuation, and a function for recording the
clean-water baseline.
