Ref. No. [UMCES] CBL 2016-015
equilibration time was slightly greater going from surface to hypolimnetic conditions. The range
in measurement differences between instrument and reference was -0.13 to 0.18 mg/L for cast 2
and -0.28 to 0.23 mg/L for cast 3. In Lake Michigan, the EXO2 exhibited a positive bias in both
portions of the water column but the magnitude was higher in the cold high DO hypolimnion.
Sensor equilibration time was similar between both trials, whether equilibrated at surface or depth.
The range in measurement differences between instrument and reference was -0.32 to -0.03 mg/L
for cast 1 and -0.20 to 0.11 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 (visitwww.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 principle of operation of the EXO2 optical dissolved oxygen sensor is based on the
well-documented concept that dissolved oxygen quenches both the intensity and the lifetime of
the luminescence associated with a carefully chosen chemical dye. The EXO2 DO sensor
operates by shining a blue light of the proper wavelength on this luminescent dye which is
immobilized in a matrix and formed into a disk. The blue light causes the immobilized dye to
luminesce and the lifetime of this dye luminescence is measured via a photodiode in the probe.
To increase the accuracy and stability of the technique, the dye is also irradiated with red light
during part of the measurement cycle to act as a reference in the determination of the
When there is no oxygen present, the lifetime of the signal is maximal; as oxygen is
introduced to the membrane surface of the sensor, the lifetime becomes shorter. Thus, the lifetime
of the luminescence is inversely proportional to the amount of oxygen present and the
relationship between the oxygen pressure outside the sensor and the lifetime can be quantified by