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Ref. No. [UMCES] CBL 2016-015

ACT VS16-06


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.


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


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.


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

luminescence lifetime.

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