Measurements of CDOM absorption spectra using different Instruments and techniques: A round robin exercise and extensive field data set.

Abstract

The optical measurement of Chromophoric Dissolved Organic Matter (CDOM) throughout the open-ocean and coastal regions has played a crucial role in the development of Ocean Color algorithms. However many spectrophotometric instruments equipped with 10cm cells are not sensitive enough to measure light attenuation from CDOM in open ocean or case 1 waters. One solution is to significantly increase the optical path length, which gives the photons of light a greater probability of being absorbed before reaching the detector. Liquid waveguide capillary cells (LWCC), integrating cavity absorption meters (ICAM), and Wetlabs absorption attenuation meters have all become prominent instruments in the community for making long path length measurements. However limitations arise due to the loss of light from scattering, spectral offsets caused by temp and salinity offsets, and cell contamination with subsequent micro-bubble formation. An extensive round robin comparison was carried out with versions of all these instruments at NASA Goddard Space Flight Center in the fall of 2013. It was part of an ongoing CDOM workshop with an international committee. Many new insights pertaining to the methodology and results of the measurements will be presented along with an extensive field data set of LWCC measurements.