Advanced Methods for Characterizing the Immersion Factor of Irradiance Sensors

Two new immersion factor methods are evaluated by comparing them with the so-called traditional (or incremental) method. For the first method, the optical measurements taken at discrete water depths are substituted by continuous profiles created by removing the water from the water tank used in the experimental procedure at a constant flow rate with a pump. In the second method, the commonly used large tank is replaced by a small water vessel with sidewall baffles, which permits the use of a quality-assured and reproducible volume of water. The summary of the validation results produced for the different methods show a significant convergence of the two new methods with the traditional method with differences generally well below 1%. The average repeatability for single-sensor characterizations (across seven wavelengths) of the three methods are very similar and approximately 1%. The evaluation of the continuous method demonstrates its full applicability in the determination of immersion factors with a significant time savings. The evaluation of the small water vessel demonstrates the possibility of significantly reducing the size of the tank (along with decreasing the execution time) and permitting a completely reproducible methodology (pure water). The small tank approach readily permits the isolation and quantification of individual sources of uncertainty, the results of which confirm the following aspects of the experimental methodology: a) pure water is preferred over tap water, b) the water should not be recycled (so it does not age), c) bubbles should be removed from all wetted surfaces, d) the water surface should be kept as clean as possible, e) sidewall reflections can be properly minimized with internal baffles, and f) a pure water characterization can be easily corrected to produce an appropriate seawater characterization. Within the context of experimental efficiency and reproducibility, this study suggests the combination of a small tank with a constant flow pump would be an optimal system.

HOOKER Stanford;  ZIBORDI Giuseppe; 

2005-11-14

AMER METEOROLOGICAL SOC

JRC30927

https://publications.jrc.ec.europa.eu/repository/handle/JRC30927,