OBJECTIVE

1
OBJECTIVE
DATA COMPARISON
The emergence of instrumentation capable of
making direct measurements of inherent optical
properties (IOPs) has enabled investigations of
the fundamental characterization of light
attenuation in aquatic environments. Evaluation
of the range, precision and accuracy of the
available instrumentation is necessary to allow
for the comparison and interpretation of ocean
field data as well as establishing the validity
of deriving other parameters from the measured
values. During the week of May 6-10, 2002 a
collaborative workshop was conducted to assess
the current capabilities for measuring the
angular scatter of light in situ. Experiments
based in reagent grade water were conducted with
uniform 600 nm, 1 micron, and 3 micron latex
micro-spheres and Maalox, an over the counter
antacid treatment. Systematic additions of the
micro-spheres and Maalox were made to
sequentially change the scattering regime from
cleanest water to single and multiple scattering
environments. Raw water collected from the
Patuxent River, MD was also used as a test media.
RUN 3 Single Scattering GASM and UA-VSM track
the scaled theoretical Mie curve well between 32
and 146. (note Mie is ac-9 c m-1 measurement
scaled) Deviations at near forward angles are
due to instrument limitations near the incident
beam. In the backward direction GASM sensitivity
is low at angles greater than 150. Inversion of
the UA-VSM VSF measurement in this region is
caused by instrument glint resulting from
inefficient light trapping. ECO-VSF reads
substantially above range at 100. Beta Boy
single point values align with VSF, although
discrepancies in HS-6 and Beta Boy measurements
are evident among the individual instruments
within the same medium.
EXPERIMENTS
RUN 3 Single Scattering GASM and UA-VSM track
the theoretical Mie curve between 27 and 115.
Deviations are comparable to the 596 nm beads at
near forward angles. Both instruments detect the
leveling out of the VSF between 110 and 140.
In the backward direction, GASM sensitivity is
limited at angles greater than 150. The UA VSM
tracks the scaled Mie curve through 175.
ECO-VSF reads below range at 100. Overall
tracking of the Mie curve by the three point
measurements are improved over the 596 nm bead
test. Beta Boy and HS-6 measurements appear
coincident and accurate. (note additional
attenuation corrections to avoid assumptions
inherent in the instrument design have not been
applied.)
Beads Incremental bead additions were made to
400-450 L of Type A reagent grade water from a
Barnstead E-Pure System. Following a blank or
water measurement, sphere additions were first
mixed in a 20 l carboy of water and then mixed
into the central tank. Simultaneous measurements
were obtained by removing a 20 l volume to fill
the LISST chamber, VABAM, and two ac-9s which
were interconnected into a flow through system
with shielded Tygon tubing. A 5 L aliquot was
sent to the Ukrainian VSM while GASM, HS-6, Beta
Instruments, and ECO-VSF were immersed in the
tank. The solution in the tank was mixed with an
SBE 3000 pump. Measurements were made in the
flow through system at stopped flow by valve
termination of the tubing. Maalox A large
3x3x12 tank accommodated all of the
instruments for the Maalox test. The tank was
filled with tap water and allowed to filter
overnight through a standard diatomaceous earth
pool filter followed by UV treatment. The
solution was homogenized between Maalox
additions by pump circulation without
filtration. Patuxent River Water Collected May
9, 2000 from UMCES Chesapeake Biological
Laboratory, Solomons, MD from an outdoor flowing
seawater line. Raw water intake was from 2 m
depth at the end of the CBL pier. Water passes
through a large screen to prevent macro organisms
from going into the system. T 17.5 ºC, PSU
14.6. Data not shown. Data Data sets were
independently processed by teams of the
participants. This poster presents the
instruments compared to scaled Mie spectra (ac-9
C m-1 measurement) at the common wavelengths in
the green spectral region (532-555 nm) by
reduction of values to ?(?). For reference,
values of b and c were calculated at 532 nm.
Complete data sets as well as experimental and
instrument protocols are being made available
through a host website at UCSB OPL
opl.ucsb.edu/ScatteringWorkshop/
RUN 3 Single Scattering GASM and UA-VSM show
excellent agreement with the scaled theoretical
Mie curve throughout their respective measurement
ranges. ECO-VSF reads slightly below range at
150. Values at 100 and 125 agree well with the
Mie. HS-6 and Beta measurements at 140 track the
magnitude of the adjusted Mie but appear slightly
high.
PARTICIPANTS
RUN 4 Maalox Instruments agree reasonably well.
HS-6 value is somewhat below range.
ACKNOWLEGEMENTS