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Ref. No. [UMCES] CBL 2016-016
ACT VS16-07
5
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 were
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 Troll 9000
overestimated DO when transitioning rapidly from the hypolimnetic equilibration into the warmer
and high DO surface water. Conversely when equilibrate in the surface water the Troll RDO
underestimated DO levels when rapidly transitioned into the colder, low DO hypolimnion. The
range in measurement differences between instrument and reference was 0.04 to 0.41 mg/L for cast
2 and -0.35 to 0.23 mg/L for cast 3. (Note: cast 1 was aborted and redone as cast 3). For Lake
Michigan, the Troll 9000 underestimated DO when transitioning rapidly from surface equilibration
into a colder, high DO hypolimnion. Conversely when equilibrate in the hypolimnion the Troll
RDO overestimated DO levels when rapidly transitioned into the warmer, lower DO surface
waters. The range in measurement differences between instrument and reference was -0.59 to 0.07
mg/L for cast 1 and -0.11 to 0.54 mg/L for cast 2. In both cases the Troll RDO appeared to
approach equilibrium by the seventh minute and the offsets declined to around 0.10 – 0.15 mg/L.
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
performance characteristics of commercially available DO sensors when applied in real world
applications in a diverse range of coastal environments.
INSTRUMENT TECHNOLOGY TESTED
The In-Situ Rugged Dissolved Oxygen (RDO
®
) Sensor measures dissolved oxygen (DO)
using the latest advancements in optical measurement technology. By improving upon the