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Ref. No. [UMCES] CBL 2016-011
ACT VS16-02
5
14 mg/L. A linear regression of the composited data (r
2
= 0.998; p<0.0001)) had a slope of 0.987
and intercept of -0.150.
The PME miniDOT was evaluated in a profiling field test in the Great Lakes at two
separate locations in order to experience transitions from surface waters into both normoxic and
hypoxic hypolimnion. In Muskegon Lake, the temperature ranged from 21.0
o
C at the surface to
13.5
o
C in the hypolimnion, with corresponding DO concentrations of 7.8 and 2.8 mg/L,
respectively. In Lake Michigan, the temperature ranged from 21.0
o
C at the surface to 4.1
o
C in the
hypolimnion, with corresponding DO concentrations of 8.6 and 12.6 mg/L, respectively. Two
profiling trials were conducted at each location. The first trial involved equilibrating test
instruments at the surface (3m) for ten minutes and then collecting three Niskin bottle samples at
one minute intervals. Following the third sample, the rosette was quickly profiled into the
hypolimnion where samples were collected immediately upon arrival and then each minute for the
next 6 minutes. The second trial was performed in the reverse direction. For Muskegon Lake, the
miniDOT exhibited a negative bias in the colder, low DO hypolimnion and a positive bias in the
warm, normoxic surface water over both of the trials. The miniDOT appeared to reach
equilibration after 7 minutes but still exhibited final offsets of approximately 0.2 mg/L following
the profiled transitions. The range in measurement differences between instrument and reference
was -0.24 to 0.75 mg/L for cast 2 and -0.57 to 0.14 mg/L for cast 3 (cast 1 was aborted and redone
as cast 3). For Lake Michigan, during cast 1 the miniDOT was well matched during surface
equilibration and then exhibited a strong negative bias when rapidly transitioned to the cold high
DO hypolimnion. The sensor did not fully equilibrate after 7 minutes and ended at -0.8 mg/L
against the reference. For cast 2, there was a negative offset of -0.6 mg/L when equilibrated in the
hypolimnion and a positive bias when rapidly transitioned into the warm normoxic surface. The
sensor appeared to reach equilibration after 7 minutes but with a final offset of around 0.4 mg/L
against the reference. The range in measurement differences between instrument and reference
was -2.03 to 0.03 mg/L for cast 1 and -0.72 to 1.63 mg/L for cast 2.
BACKGROUND AND OBJECTIVES
Instrument performance verification is necessary so that effective existing technologies can
be recognized and so that promising new technologies can be made available to support coastal
science, resource management and ocean observing systems. To this end, the NOAA-funded
Alliance for Coastal Technologies (ACT) serves as an unbiased, third party testbed for evaluating
sensors and sensor platforms for use in coastal environments. ACT also serves as a comprehensive
data and information clearinghouse on coastal technologies and a forum for capacity building
through workshops on specific technology topics (visit
www.act-us.info).
As part of our service to the coastal community, ACT conducted a performance verification
of commercially available, in situ dissolved oxygen (DO) sensors through the evaluation of
objective and quality assured data. The goal of ACT’s evaluation program is to provide technology
users with an independent and credible assessment of instrument performance in a variety of
environments and applications. To this end, the data and information on performance
characteristics were focused on the types of information users most need.
The fundamental objectives of this Performance Verification were to: (1) highlight the
potential capabilities of particular in situ DO sensors by demonstrating their utility in a range of
coastal environments; (2) verify the claims of manufacturers on the performance characteristics of
commercially available DO sensors when tested in a controlled laboratory setting, and (3) verify